update

content/courses/prog-intro/homeworks/sum/ParseIntExample.java

@@ -5,8 +5,7 @@ public class ParseIntExample {
     public static void main(String[] args) {
         String s = "123";
         int sum = 321;
-        //! sum = sum + s;
+        String result = s + sum;
-        sum = sum + Integer.parseInt(s);
+        System.out.println(result);
-        System.out.println(sum);
     }
 }

content/courses/prog-intro/homeworks/sum/Sum.java

@@ -1,17 +1,32 @@
 // Sum.java
 
 public class Sum {
+
     public static void main(String[] args) {
-        System.out.println("number of arguments: " + args.length);
-        
         int sum = 0;
         for (String argument : args) {
-            sum = sum + argument;
+            StringBuilder number = new StringBuilder(); // we will form numbers here using StringBuilder
-            System.out.println(argument);
+            for (char c : argument.toCharArray()) {
-            System.out.println(sum);
+                if (!Character.isWhitespace(c)) {
+                    // if character is not whitespace
+                    number.append(c); // concatenate new digit
+                } else {
+                    // if character is whitespace
+                    if (!number.isEmpty()) {
+                        // if number is not empty
+                        sum = sum + Integer.parseInt(number.toString()); // add number to sum
+                    }
+                    number = new StringBuilder(); // empty the number by creating new empty StringBuilder
+                }
+            }
+
+            // check for any remaining digits in number
+            if (!number.isEmpty()) {
+                // if number is not empty
+                sum = sum + Integer.parseInt(number.toString()); // add number to sum
+            }
         }
-        
+
         System.out.println(sum);
     }
 }
-

content/courses/prog-intro/homeworks/sum/_index.md

@@ -235,11 +235,226 @@ public class ParseIntExample {
     public static void main(String[] args) {
         String s = "123";
         int sum = 321;
-        //! sum = sum + s;
+        //! int result = s + sum;
-        sum = sum + Integer.parseInt(s);
-        System.out.println(sum);
     }
 }
 ```
 
 The commented out line (`//!`) would have given us an exception.
+
+```bash
+$ javac ParseIntExample.java
+ParseIntExample.java:8: error: incompatible types: String cannot be converted to int
+        int result = s + sum;
+                       ^
+1 error
+```
+
+> [!IMPORTANT]
+> Please note that if we change `result` data type to `String`, the code will work just fine.
+> ```java
+> // ParseIntExample.java
+> public class ParseIntExample {
+> 
+>     public static void main(String[] args) {
+>         String s = "123";
+>         int sum = 321;
+>         String result = s + sum;
+>         System.out.println(result);
+>     }
+> }
+> ```
+> ```bash
+> $ javac ParseIntExample.java && java ParseIntExample 
+> 123321
+> ```
+> In this case `sum` will be ***automatically casted*** to `String` and two strings will just concatenate.
+
+So we figured out that we need to cast `argument` to integer type. Let's change our code and test it.
+
+```java
+// Sum.java
+
+public class Sum {
+    public static void main(String[] args) {
+        System.out.println("number of arguments: " + args.length);
+        
+        int sum = 0;
+        for (String argument : args) {
+            sum = sum + Ineteger.parseInt(argument);
+            System.out.println(argument);
+            System.out.println(sum);
+        }
+        
+        System.out.println(sum);
+    }
+}
+```
+
+```java
+// Sum.java
+
+public class Sum {
+    public static void main(String[] args) {
+        System.out.println("number of arguments: " + args.length);
+
+        int sum = 0;
+        for (String argument : args) {
+            sum = sum + Integer.parseInt(argument);
+            System.out.println(
+                "current argument: " + argument + ", current sum: " + sum
+            );
+        }
+
+        System.out.println("final sum: " + sum);
+    }
+}
+```
+```bash
+$ java Sum 1 2 3
+number of arguments: 3
+current argument: 1, current sum: 1
+current argument: 2, current sum: 3
+current argument: 3, current sum: 6
+final sum: 6
+```
+```bash
+$ java Sum 1 2 -3
+number of arguments: 3
+current argument: 1, current sum: 1
+current argument: 2, current sum: 3
+current argument: -3, current sum: 0
+final sum: 0
+```
+```bash
+$ java Sum "1 2 3"
+number of arguments: 1
+Exception in thread "main" java.lang.NumberFormatException: For input string: "1 2 3"
+	at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:67)
+	at java.base/java.lang.Integer.parseInt(Integer.java:662)
+	at java.base/java.lang.Integer.parseInt(Integer.java:778)
+	at Sum.main(Sum.java:9)
+```
+
+As we can see because we have only 1 argument (`"1 2 3"`) we try to parse it as an integer but `"1 2 3"` contains empty spaces, so it can't be parsed as an integer.
+
+We need to manually extract numeric values from the `argument` string.
+
+In order to do that we will iterate over each symbol of the `argument` string and extract numeric values. 
+
+We will have another variable `number` of `String` type in which we will be storing extracted numeric values.
+
+For every character or symbol in the string, we will check it to be an empty space or a digit. If it is a digit, we will add/concatenate with `number`, and if it is an empty space, we will add the numeric value of `number` to `sum` and then assign empty string to `number` because we reached the end of the current number and are ready to move to the next one.
+
+> [!IMPORTANT]
+> It is important to add numeric value of `number` (if it's not empty) to `sum` after we iterated over the entire string because if it ends like this `"1 2 3"`, we don't nessesarily have an empty space at the end so `"3"` (in this case) will be stored in `number` but NOT added to `sum`.
+
+Let's implement those ideas into solution. We will get rid of all the `println` messages so it's not drawing our attention.
+
+> [!NOTE]
+> Also I want to point out that we can't just iterate over `String`. First we need to turn it into an ***array of characters*** using [`String.toCharArray()`](https://docs.oracle.com/javase/8/docs/api/java/lang/String.html#toCharArray--) method.
+
+> [!NOTE]
+> We will be checking for an empty space using [`Character.isWhitespace(char ch)`](https://docs.oracle.com/javase/8/docs/api/java/lang/Character.html#isWhitespace-char-) which outputs `true` or `false` accordingly.
+
+```java
+// Sum.java
+
+public class Sum {
+
+    public static void main(String[] args) {
+        int sum = 0;
+        for (String argument : args) {
+            String number = ""; // we will form numbers here
+            for (char c : argument.toCharArray()) {
+                if (!Character.isWhitespace(c)) {
+                    // if character is not whitespace
+                    number = number + c; // concatenate new digit
+                } else {
+                    // if character is whitespace
+                    if (!number.isEmpty()) {
+                        // if number is not empty
+                        sum = sum + Integer.parseInt(number); // add number to sum
+                    }
+                    number = ""; // empty the number
+                }
+            }
+
+            // check for any remaining digits in number
+            if (!number.isEmpty()) {
+                // if number is not empty
+                sum = sum + Integer.parseInt(number); // add number to sum
+            }
+        }
+
+        System.out.println(sum);
+    }
+}
+```
+
+```bash
+$ java Sum 1 2 3
+6
+```
+```bash
+$ java Sum 1 2 -3
+0
+```
+```bash
+$ java Sum "1 2 3"
+6
+```
+```bash
+$ java Sum "1 2" " 3"
+6
+```
+```bash
+$ java Sum " "
+0
+```
+
+This code works and passes all the tests! 
+
+But can we improve it? One efficiency improvement we can make is to get rid of concatenating strings. You can read why it's bad [here](https://stackoverflow.com/questions/18561424/using-for-strings-in-a-loop-is-it-bad-practice) or [here](https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.reddit.com/r/javahelp/comments/19e9jic/question_about_dont_concat_string_in_a_loop/&ved=2ahUKEwiCpva0y-GTAxUeB9sEHbvzHj4QFnoECCAQAQ&usg=AOvVaw3gk39Xk7Jz9_PmKVIO81nK).
+
+We can use [StringBuilder](https://docs.oracle.com/javase/8/docs/api/java/lang/StringBuilder.html) because it can ***build*** strings more efficiently. 
+
+So here's the updated code
+
+```java
+// Sum.java
+
+public class Sum {
+
+    public static void main(String[] args) {
+        int sum = 0;
+        for (String argument : args) {
+            StringBuilder number = new StringBuilder(); // we will form numbers here using StringBuilder
+            for (char c : argument.toCharArray()) {
+                if (!Character.isWhitespace(c)) {
+                    // if character is not whitespace
+                    number.append(c); // concatenate new digit
+                } else {
+                    // if character is whitespace
+                    if (!number.isEmpty()) {
+                        // if number is not empty
+                        sum = sum + Integer.parseInt(number.toString()); // add number to sum
+                    }
+                    number = new StringBuilder(); // empty the number by creating new empty StringBuilder
+                }
+            }
+
+            // check for any remaining digits in number
+            if (!number.isEmpty()) {
+                // if number is not empty
+                sum = sum + Integer.parseInt(number.toString()); // add number to sum
+            }
+        }
+
+        System.out.println(sum);
+    }
+}
+```
+
+> [!IMPORTANT]
+> Note, that we can't just do `Integer.parseInt()`

public/courses/prog-intro/homeworks/sum/ParseIntExample.java

@@ -5,8 +5,7 @@ public class ParseIntExample {
     public static void main(String[] args) {
         String s = "123";
         int sum = 321;
-        //! sum = sum + s;
+        String result = s + sum;
-        sum = sum + Integer.parseInt(s);
+        System.out.println(result);
-        System.out.println(sum);
     }
 }

public/courses/prog-intro/homeworks/sum/Sum.java

@@ -1,17 +1,32 @@
 // Sum.java
 
 public class Sum {
+
     public static void main(String[] args) {
-        System.out.println("number of arguments: " + args.length);
-        
         int sum = 0;
         for (String argument : args) {
-            sum = sum + argument;
+            StringBuilder number = new StringBuilder(); // we will form numbers here using StringBuilder
-            System.out.println(argument);
+            for (char c : argument.toCharArray()) {
-            System.out.println(sum);
+                if (!Character.isWhitespace(c)) {
+                    // if character is not whitespace
+                    number.append(c); // concatenate new digit
+                } else {
+                    // if character is whitespace
+                    if (!number.isEmpty()) {
+                        // if number is not empty
+                        sum = sum + Integer.parseInt(number.toString()); // add number to sum
+                    }
+                    number = new StringBuilder(); // empty the number by creating new empty StringBuilder
+                }
+            }
+
+            // check for any remaining digits in number
+            if (!number.isEmpty()) {
+                // if number is not empty
+                sum = sum + Integer.parseInt(number.toString()); // add number to sum
+            }
         }
-        
+
         System.out.println(sum);
     }
 }
-

public/courses/prog-intro/homeworks/sum/index.html

@@ -35,7 +35,7 @@ java Sum 1 2 -3 Expected output: 0." /><link rel="canonical" href="http://localh
 Examples:
 java Sum 1 2 3 Expected output: 6.
 java Sum 1 2 -3 Expected output: 0.">
-  <meta itemprop="wordCount" content="919">
+  <meta itemprop="wordCount" content="1840">
   <meta name="twitter:card" content="summary">
   <meta name="twitter:title" content="Sum">
   <meta name="twitter:description" content="Task You need to create a Sum class which will sum integers from command line arguments and output the sum to console.
@@ -775,9 +775,7 @@ java Sum 1 2 -3 Expected output: 0.">
 </span></span><span style="display:flex;"><span>    <span style="color:#66d9ef">public</span> <span style="color:#66d9ef">static</span> <span style="color:#66d9ef">void</span> <span style="color:#a6e22e">main</span>(String<span style="color:#f92672">[]</span> args) {
 </span></span><span style="display:flex;"><span>        String s <span style="color:#f92672">=</span> <span style="color:#e6db74">&#34;123&#34;</span>;
 </span></span><span style="display:flex;"><span>        <span style="color:#66d9ef">int</span> sum <span style="color:#f92672">=</span> 321;
-</span></span><span style="display:flex;"><span>        <span style="color:#75715e">//! sum = sum + s;</span>
+</span></span><span style="display:flex;"><span>        <span style="color:#75715e">//! int result = s + sum;</span>
-</span></span><span style="display:flex;"><span>        sum <span style="color:#f92672">=</span> sum <span style="color:#f92672">+</span> Integer.<span style="color:#a6e22e">parseInt</span>(s);
-</span></span><span style="display:flex;"><span>        System.<span style="color:#a6e22e">out</span>.<span style="color:#a6e22e">println</span>(sum);
 </span></span><span style="display:flex;"><span>    }
 </span></span><span style="display:flex;"><span>}</span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
   <button
@@ -790,6 +788,361 @@ java Sum 1 2 -3 Expected output: 0.">
 </div>
 </div>
 <p>The commented out line (<code>//!</code>) would have given us an exception.</p>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>$ javac ParseIntExample.java
+</span></span><span style="display:flex;"><span>ParseIntExample.java:8: error: incompatible types: String cannot be converted to int
+</span></span><span style="display:flex;"><span>        int result <span style="color:#f92672">=</span> s + sum;
+</span></span><span style="display:flex;"><span>                       ^
+</span></span><span style="display:flex;"><span><span style="color:#ae81ff">1</span> error</span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<div class="hx:overflow-x-auto hx:mt-6 hx:flex hx:flex-col hx:rounded-lg hx:border hx:py-4 hx:px-4 hx:border-gray-200 hx:contrast-more:border-current hx:contrast-more:dark:border-current hx:border-purple-200 hx:bg-purple-100 hx:text-purple-900 hx:dark:border-purple-200/30 hx:dark:bg-purple-900/30 hx:dark:text-purple-200">
+  <p class="hx:flex hx:items-center hx:font-medium"><svg height=16px class="hx:inline-block hx:align-middle hx:mr-2" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor" aria-hidden="true"><path stroke-linecap="round" stroke-linejoin="round" d="M13 16h-1v-4h-1m1-4h.01M21 12a9 9 0 11-18 0 9 9 0 0118 0z"/></svg>Important</p>
+
+  <div class="hx:w-full hx:min-w-0 hx:leading-7">
+    <div class="hx:mt-6 hx:leading-7 hx:first:mt-0"><p>Please note that if we change <code>result</code> data type to <code>String</code>, the code will work just fine.</p>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-java" data-lang="java"><span style="display:flex;"><span><span style="color:#75715e">// ParseIntExample.java</span>
+</span></span><span style="display:flex;"><span><span style="color:#66d9ef">public</span> <span style="color:#66d9ef">class</span> <span style="color:#a6e22e">ParseIntExample</span> {
+</span></span><span style="display:flex;"><span>
+</span></span><span style="display:flex;"><span>    <span style="color:#66d9ef">public</span> <span style="color:#66d9ef">static</span> <span style="color:#66d9ef">void</span> <span style="color:#a6e22e">main</span>(String<span style="color:#f92672">[]</span> args) {
+</span></span><span style="display:flex;"><span>        String s <span style="color:#f92672">=</span> <span style="color:#e6db74">&#34;123&#34;</span>;
+</span></span><span style="display:flex;"><span>        <span style="color:#66d9ef">int</span> sum <span style="color:#f92672">=</span> 321;
+</span></span><span style="display:flex;"><span>        String result <span style="color:#f92672">=</span> s <span style="color:#f92672">+</span> sum;
+</span></span><span style="display:flex;"><span>        System.<span style="color:#a6e22e">out</span>.<span style="color:#a6e22e">println</span>(result);
+</span></span><span style="display:flex;"><span>    }
+</span></span><span style="display:flex;"><span>}</span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>$ javac ParseIntExample.java <span style="color:#f92672">&amp;&amp;</span> java ParseIntExample 
+</span></span><span style="display:flex;"><span><span style="color:#ae81ff">123321</span></span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<p>In this case <code>sum</code> will be <em><strong>automatically casted</strong></em> to <code>String</code> and two strings will just concatenate.</p></div>
+  </div>
+</div>
+<p>So we figured out that we need to cast <code>argument</code> to integer type. Let&rsquo;s change our code and test it.</p>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-java" data-lang="java"><span style="display:flex;"><span><span style="color:#75715e">// Sum.java</span>
+</span></span><span style="display:flex;"><span>
+</span></span><span style="display:flex;"><span><span style="color:#66d9ef">public</span> <span style="color:#66d9ef">class</span> <span style="color:#a6e22e">Sum</span> {
+</span></span><span style="display:flex;"><span>    <span style="color:#66d9ef">public</span> <span style="color:#66d9ef">static</span> <span style="color:#66d9ef">void</span> <span style="color:#a6e22e">main</span>(String<span style="color:#f92672">[]</span> args) {
+</span></span><span style="display:flex;"><span>        System.<span style="color:#a6e22e">out</span>.<span style="color:#a6e22e">println</span>(<span style="color:#e6db74">&#34;number of arguments: &#34;</span> <span style="color:#f92672">+</span> args.<span style="color:#a6e22e">length</span>);
+</span></span><span style="display:flex;"><span>        
+</span></span><span style="display:flex;"><span>        <span style="color:#66d9ef">int</span> sum <span style="color:#f92672">=</span> 0;
+</span></span><span style="display:flex;"><span>        <span style="color:#66d9ef">for</span> (String argument : args) {
+</span></span><span style="display:flex;"><span>            sum <span style="color:#f92672">=</span> sum <span style="color:#f92672">+</span> Ineteger.<span style="color:#a6e22e">parseInt</span>(argument);
+</span></span><span style="display:flex;"><span>            System.<span style="color:#a6e22e">out</span>.<span style="color:#a6e22e">println</span>(argument);
+</span></span><span style="display:flex;"><span>            System.<span style="color:#a6e22e">out</span>.<span style="color:#a6e22e">println</span>(sum);
+</span></span><span style="display:flex;"><span>        }
+</span></span><span style="display:flex;"><span>        
+</span></span><span style="display:flex;"><span>        System.<span style="color:#a6e22e">out</span>.<span style="color:#a6e22e">println</span>(sum);
+</span></span><span style="display:flex;"><span>    }
+</span></span><span style="display:flex;"><span>}</span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-java" data-lang="java"><span style="display:flex;"><span><span style="color:#75715e">// Sum.java</span>
+</span></span><span style="display:flex;"><span>
+</span></span><span style="display:flex;"><span><span style="color:#66d9ef">public</span> <span style="color:#66d9ef">class</span> <span style="color:#a6e22e">Sum</span> {
+</span></span><span style="display:flex;"><span>    <span style="color:#66d9ef">public</span> <span style="color:#66d9ef">static</span> <span style="color:#66d9ef">void</span> <span style="color:#a6e22e">main</span>(String<span style="color:#f92672">[]</span> args) {
+</span></span><span style="display:flex;"><span>        System.<span style="color:#a6e22e">out</span>.<span style="color:#a6e22e">println</span>(<span style="color:#e6db74">&#34;number of arguments: &#34;</span> <span style="color:#f92672">+</span> args.<span style="color:#a6e22e">length</span>);
+</span></span><span style="display:flex;"><span>
+</span></span><span style="display:flex;"><span>        <span style="color:#66d9ef">int</span> sum <span style="color:#f92672">=</span> 0;
+</span></span><span style="display:flex;"><span>        <span style="color:#66d9ef">for</span> (String argument : args) {
+</span></span><span style="display:flex;"><span>            sum <span style="color:#f92672">=</span> sum <span style="color:#f92672">+</span> Integer.<span style="color:#a6e22e">parseInt</span>(argument);
+</span></span><span style="display:flex;"><span>            System.<span style="color:#a6e22e">out</span>.<span style="color:#a6e22e">println</span>(
+</span></span><span style="display:flex;"><span>                <span style="color:#e6db74">&#34;current argument: &#34;</span> <span style="color:#f92672">+</span> argument <span style="color:#f92672">+</span> <span style="color:#e6db74">&#34;, current sum: &#34;</span> <span style="color:#f92672">+</span> sum
+</span></span><span style="display:flex;"><span>            );
+</span></span><span style="display:flex;"><span>        }
+</span></span><span style="display:flex;"><span>
+</span></span><span style="display:flex;"><span>        System.<span style="color:#a6e22e">out</span>.<span style="color:#a6e22e">println</span>(<span style="color:#e6db74">&#34;final sum: &#34;</span> <span style="color:#f92672">+</span> sum);
+</span></span><span style="display:flex;"><span>    }
+</span></span><span style="display:flex;"><span>}</span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>$ java Sum <span style="color:#ae81ff">1</span> <span style="color:#ae81ff">2</span> <span style="color:#ae81ff">3</span>
+</span></span><span style="display:flex;"><span>number of arguments: <span style="color:#ae81ff">3</span>
+</span></span><span style="display:flex;"><span>current argument: 1, current sum: <span style="color:#ae81ff">1</span>
+</span></span><span style="display:flex;"><span>current argument: 2, current sum: <span style="color:#ae81ff">3</span>
+</span></span><span style="display:flex;"><span>current argument: 3, current sum: <span style="color:#ae81ff">6</span>
+</span></span><span style="display:flex;"><span>final sum: <span style="color:#ae81ff">6</span></span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>$ java Sum <span style="color:#ae81ff">1</span> <span style="color:#ae81ff">2</span> -3
+</span></span><span style="display:flex;"><span>number of arguments: <span style="color:#ae81ff">3</span>
+</span></span><span style="display:flex;"><span>current argument: 1, current sum: <span style="color:#ae81ff">1</span>
+</span></span><span style="display:flex;"><span>current argument: 2, current sum: <span style="color:#ae81ff">3</span>
+</span></span><span style="display:flex;"><span>current argument: -3, current sum: <span style="color:#ae81ff">0</span>
+</span></span><span style="display:flex;"><span>final sum: <span style="color:#ae81ff">0</span></span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>$ java Sum <span style="color:#e6db74">&#34;1 2 3&#34;</span>
+</span></span><span style="display:flex;"><span>number of arguments: <span style="color:#ae81ff">1</span>
+</span></span><span style="display:flex;"><span>Exception in thread <span style="color:#e6db74">&#34;main&#34;</span> java.lang.NumberFormatException: For input string: <span style="color:#e6db74">&#34;1 2 3&#34;</span>
+</span></span><span style="display:flex;"><span>	at java.base/java.lang.NumberFormatException.forInputString<span style="color:#f92672">(</span>NumberFormatException.java:67<span style="color:#f92672">)</span>
+</span></span><span style="display:flex;"><span>	at java.base/java.lang.Integer.parseInt<span style="color:#f92672">(</span>Integer.java:662<span style="color:#f92672">)</span>
+</span></span><span style="display:flex;"><span>	at java.base/java.lang.Integer.parseInt<span style="color:#f92672">(</span>Integer.java:778<span style="color:#f92672">)</span>
+</span></span><span style="display:flex;"><span>	at Sum.main<span style="color:#f92672">(</span>Sum.java:9<span style="color:#f92672">)</span></span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<p>As we can see because we have only 1 argument (<code>&quot;1 2 3&quot;</code>) we try to parse it as an integer but <code>&quot;1 2 3&quot;</code> contains empty spaces, so it can&rsquo;t be parsed as an integer.</p>
+<p>We need to manually extract numeric values from the <code>argument</code> string.</p>
+<p>In order to do that we will iterate over each symbol of the <code>argument</code> string and extract numeric values.</p>
+<p>We will have another variable <code>number</code> of <code>String</code> type in which we will be storing extracted numeric values.</p>
+<p>For every character or symbol in the string, we will check it to be an empty space or a digit. If it is a digit, we will add/concatenate with <code>number</code>, and if it is an empty space, we will add the numeric value of <code>number</code> to <code>sum</code> and then assign empty string to <code>number</code> because we reached the end of the current number and are ready to move to the next one.</p>
+<div class="hx:overflow-x-auto hx:mt-6 hx:flex hx:flex-col hx:rounded-lg hx:border hx:py-4 hx:px-4 hx:border-gray-200 hx:contrast-more:border-current hx:contrast-more:dark:border-current hx:border-purple-200 hx:bg-purple-100 hx:text-purple-900 hx:dark:border-purple-200/30 hx:dark:bg-purple-900/30 hx:dark:text-purple-200">
+  <p class="hx:flex hx:items-center hx:font-medium"><svg height=16px class="hx:inline-block hx:align-middle hx:mr-2" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor" aria-hidden="true"><path stroke-linecap="round" stroke-linejoin="round" d="M13 16h-1v-4h-1m1-4h.01M21 12a9 9 0 11-18 0 9 9 0 0118 0z"/></svg>Important</p>
+
+  <div class="hx:w-full hx:min-w-0 hx:leading-7">
+    <div class="hx:mt-6 hx:leading-7 hx:first:mt-0"><p>It is important to add numeric value of <code>number</code> (if it&rsquo;s not empty) to <code>sum</code> after we iterated over the entire string because if it ends like this <code>&quot;1 2 3&quot;</code>, we don&rsquo;t nessesarily have an empty space at the end so <code>&quot;3&quot;</code> (in this case) will be stored in <code>number</code> but NOT added to <code>sum</code>.</p></div>
+  </div>
+</div>
+<p>Let&rsquo;s implement those ideas into solution. We will get rid of all the <code>println</code> messages so it&rsquo;s not drawing our attention.</p>
+<div class="hx:overflow-x-auto hx:mt-6 hx:flex hx:flex-col hx:rounded-lg hx:border hx:py-4 hx:px-4 hx:border-gray-200 hx:contrast-more:border-current hx:contrast-more:dark:border-current hx:border-blue-200 hx:bg-blue-100 hx:text-blue-900 hx:dark:border-blue-200/30 hx:dark:bg-blue-900/30 hx:dark:text-blue-200">
+  <p class="hx:flex hx:items-center hx:font-medium"><svg height=16px class="hx:inline-block hx:align-middle hx:mr-2" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor" aria-hidden="true"><path stroke-linecap="round" stroke-linejoin="round" d="M13 16h-1v-4h-1m1-4h.01M21 12a9 9 0 11-18 0 9 9 0 0118 0z"/></svg>Note</p>
+
+  <div class="hx:w-full hx:min-w-0 hx:leading-7">
+    <div class="hx:mt-6 hx:leading-7 hx:first:mt-0"><p>Also I want to point out that we can&rsquo;t just iterate over <code>String</code>. First we need to turn it into an <em><strong>array of characters</strong></em> using <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html#toCharArray--"target="_blank" rel="noopener"><code>String.toCharArray()</code></a> method.</p></div>
+  </div>
+</div>
+<div class="hx:overflow-x-auto hx:mt-6 hx:flex hx:flex-col hx:rounded-lg hx:border hx:py-4 hx:px-4 hx:border-gray-200 hx:contrast-more:border-current hx:contrast-more:dark:border-current hx:border-blue-200 hx:bg-blue-100 hx:text-blue-900 hx:dark:border-blue-200/30 hx:dark:bg-blue-900/30 hx:dark:text-blue-200">
+  <p class="hx:flex hx:items-center hx:font-medium"><svg height=16px class="hx:inline-block hx:align-middle hx:mr-2" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor" aria-hidden="true"><path stroke-linecap="round" stroke-linejoin="round" d="M13 16h-1v-4h-1m1-4h.01M21 12a9 9 0 11-18 0 9 9 0 0118 0z"/></svg>Note</p>
+
+  <div class="hx:w-full hx:min-w-0 hx:leading-7">
+    <div class="hx:mt-6 hx:leading-7 hx:first:mt-0"><p>We will be checking for an empty space using <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Character.html#isWhitespace-char-"target="_blank" rel="noopener"><code>Character.isWhitespace(char ch)</code></a> which outputs <code>true</code> or <code>false</code> accordingly.</p></div>
+  </div>
+</div>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-java" data-lang="java"><span style="display:flex;"><span><span style="color:#75715e">// Sum.java</span>
+</span></span><span style="display:flex;"><span>
+</span></span><span style="display:flex;"><span><span style="color:#66d9ef">public</span> <span style="color:#66d9ef">class</span> <span style="color:#a6e22e">Sum</span> {
+</span></span><span style="display:flex;"><span>
+</span></span><span style="display:flex;"><span>    <span style="color:#66d9ef">public</span> <span style="color:#66d9ef">static</span> <span style="color:#66d9ef">void</span> <span style="color:#a6e22e">main</span>(String<span style="color:#f92672">[]</span> args) {
+</span></span><span style="display:flex;"><span>        <span style="color:#66d9ef">int</span> sum <span style="color:#f92672">=</span> 0;
+</span></span><span style="display:flex;"><span>        <span style="color:#66d9ef">for</span> (String argument : args) {
+</span></span><span style="display:flex;"><span>            String number <span style="color:#f92672">=</span> <span style="color:#e6db74">&#34;&#34;</span>; <span style="color:#75715e">// we will form numbers here</span>
+</span></span><span style="display:flex;"><span>            <span style="color:#66d9ef">for</span> (<span style="color:#66d9ef">char</span> c : argument.<span style="color:#a6e22e">toCharArray</span>()) {
+</span></span><span style="display:flex;"><span>                <span style="color:#66d9ef">if</span> (<span style="color:#f92672">!</span>Character.<span style="color:#a6e22e">isWhitespace</span>(c)) {
+</span></span><span style="display:flex;"><span>                    <span style="color:#75715e">// if character is not whitespace</span>
+</span></span><span style="display:flex;"><span>                    number <span style="color:#f92672">=</span> number <span style="color:#f92672">+</span> c; <span style="color:#75715e">// concatenate new digit</span>
+</span></span><span style="display:flex;"><span>                } <span style="color:#66d9ef">else</span> {
+</span></span><span style="display:flex;"><span>                    <span style="color:#75715e">// if character is whitespace</span>
+</span></span><span style="display:flex;"><span>                    <span style="color:#66d9ef">if</span> (<span style="color:#f92672">!</span>number.<span style="color:#a6e22e">isEmpty</span>()) {
+</span></span><span style="display:flex;"><span>                        <span style="color:#75715e">// if number is not empty</span>
+</span></span><span style="display:flex;"><span>                        sum <span style="color:#f92672">=</span> sum <span style="color:#f92672">+</span> Integer.<span style="color:#a6e22e">parseInt</span>(number); <span style="color:#75715e">// add number to sum</span>
+</span></span><span style="display:flex;"><span>                    }
+</span></span><span style="display:flex;"><span>                    number <span style="color:#f92672">=</span> <span style="color:#e6db74">&#34;&#34;</span>; <span style="color:#75715e">// empty the number</span>
+</span></span><span style="display:flex;"><span>                }
+</span></span><span style="display:flex;"><span>            }
+</span></span><span style="display:flex;"><span>
+</span></span><span style="display:flex;"><span>            <span style="color:#75715e">// check for any remaining digits in number</span>
+</span></span><span style="display:flex;"><span>            <span style="color:#66d9ef">if</span> (<span style="color:#f92672">!</span>number.<span style="color:#a6e22e">isEmpty</span>()) {
+</span></span><span style="display:flex;"><span>                <span style="color:#75715e">// if number is not empty</span>
+</span></span><span style="display:flex;"><span>                sum <span style="color:#f92672">=</span> sum <span style="color:#f92672">+</span> Integer.<span style="color:#a6e22e">parseInt</span>(number); <span style="color:#75715e">// add number to sum</span>
+</span></span><span style="display:flex;"><span>            }
+</span></span><span style="display:flex;"><span>        }
+</span></span><span style="display:flex;"><span>
+</span></span><span style="display:flex;"><span>        System.<span style="color:#a6e22e">out</span>.<span style="color:#a6e22e">println</span>(sum);
+</span></span><span style="display:flex;"><span>    }
+</span></span><span style="display:flex;"><span>}</span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>$ java Sum <span style="color:#ae81ff">1</span> <span style="color:#ae81ff">2</span> <span style="color:#ae81ff">3</span>
+</span></span><span style="display:flex;"><span><span style="color:#ae81ff">6</span></span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>$ java Sum <span style="color:#ae81ff">1</span> <span style="color:#ae81ff">2</span> -3
+</span></span><span style="display:flex;"><span><span style="color:#ae81ff">0</span></span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>$ java Sum <span style="color:#e6db74">&#34;1 2 3&#34;</span>
+</span></span><span style="display:flex;"><span><span style="color:#ae81ff">6</span></span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>$ java Sum <span style="color:#e6db74">&#34;1 2&#34;</span> <span style="color:#e6db74">&#34; 3&#34;</span>
+</span></span><span style="display:flex;"><span><span style="color:#ae81ff">6</span></span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>$ java Sum <span style="color:#e6db74">&#34; &#34;</span>
+</span></span><span style="display:flex;"><span><span style="color:#ae81ff">0</span></span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<p>This code works and passes all the tests!</p>
+<p>But can we improve it? One efficiency improvement we can make is to get rid of concatenating strings. You can read why it&rsquo;s bad <a href="https://stackoverflow.com/questions/18561424/using-for-strings-in-a-loop-is-it-bad-practice"target="_blank" rel="noopener">here</a> or <a href="https://www.google.com/url?sa=t&amp;source=web&amp;rct=j&amp;opi=89978449&amp;url=https://www.reddit.com/r/javahelp/comments/19e9jic/question_about_dont_concat_string_in_a_loop/&amp;ved=2ahUKEwiCpva0y-GTAxUeB9sEHbvzHj4QFnoECCAQAQ&amp;usg=AOvVaw3gk39Xk7Jz9_PmKVIO81nK"target="_blank" rel="noopener">here</a>.</p>
+<p>We can use <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/StringBuilder.html"target="_blank" rel="noopener">StringBuilder</a> because it can <em><strong>build</strong></em> strings more efficiently.</p>
+<p>So here&rsquo;s the updated code</p>
+<div class="hextra-code-block hx:relative hx:mt-6 hx:first:mt-0 hx:group/code">
+
+<div><div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-java" data-lang="java"><span style="display:flex;"><span><span style="color:#75715e">// Sum.java</span>
+</span></span><span style="display:flex;"><span>
+</span></span><span style="display:flex;"><span><span style="color:#66d9ef">public</span> <span style="color:#66d9ef">class</span> <span style="color:#a6e22e">Sum</span> {
+</span></span><span style="display:flex;"><span>
+</span></span><span style="display:flex;"><span>    <span style="color:#66d9ef">public</span> <span style="color:#66d9ef">static</span> <span style="color:#66d9ef">void</span> <span style="color:#a6e22e">main</span>(String<span style="color:#f92672">[]</span> args) {
+</span></span><span style="display:flex;"><span>        <span style="color:#66d9ef">int</span> sum <span style="color:#f92672">=</span> 0;
+</span></span><span style="display:flex;"><span>        <span style="color:#66d9ef">for</span> (String argument : args) {
+</span></span><span style="display:flex;"><span>            StringBuilder number <span style="color:#f92672">=</span> <span style="color:#66d9ef">new</span> StringBuilder(); <span style="color:#75715e">// we will form numbers here using StringBuilder</span>
+</span></span><span style="display:flex;"><span>            <span style="color:#66d9ef">for</span> (<span style="color:#66d9ef">char</span> c : argument.<span style="color:#a6e22e">toCharArray</span>()) {
+</span></span><span style="display:flex;"><span>                <span style="color:#66d9ef">if</span> (<span style="color:#f92672">!</span>Character.<span style="color:#a6e22e">isWhitespace</span>(c)) {
+</span></span><span style="display:flex;"><span>                    <span style="color:#75715e">// if character is not whitespace</span>
+</span></span><span style="display:flex;"><span>                    number.<span style="color:#a6e22e">append</span>(c); <span style="color:#75715e">// concatenate new digit</span>
+</span></span><span style="display:flex;"><span>                } <span style="color:#66d9ef">else</span> {
+</span></span><span style="display:flex;"><span>                    <span style="color:#75715e">// if character is whitespace</span>
+</span></span><span style="display:flex;"><span>                    <span style="color:#66d9ef">if</span> (<span style="color:#f92672">!</span>number.<span style="color:#a6e22e">isEmpty</span>()) {
+</span></span><span style="display:flex;"><span>                        <span style="color:#75715e">// if number is not empty</span>
+</span></span><span style="display:flex;"><span>                        sum <span style="color:#f92672">=</span> sum <span style="color:#f92672">+</span> Integer.<span style="color:#a6e22e">parseInt</span>(number.<span style="color:#a6e22e">toString</span>()); <span style="color:#75715e">// add number to sum</span>
+</span></span><span style="display:flex;"><span>                    }
+</span></span><span style="display:flex;"><span>                    number <span style="color:#f92672">=</span> <span style="color:#66d9ef">new</span> StringBuilder(); <span style="color:#75715e">// empty the number by creating new empty StringBuilder</span>
+</span></span><span style="display:flex;"><span>                }
+</span></span><span style="display:flex;"><span>            }
+</span></span><span style="display:flex;"><span>
+</span></span><span style="display:flex;"><span>            <span style="color:#75715e">// check for any remaining digits in number</span>
+</span></span><span style="display:flex;"><span>            <span style="color:#66d9ef">if</span> (<span style="color:#f92672">!</span>number.<span style="color:#a6e22e">isEmpty</span>()) {
+</span></span><span style="display:flex;"><span>                <span style="color:#75715e">// if number is not empty</span>
+</span></span><span style="display:flex;"><span>                sum <span style="color:#f92672">=</span> sum <span style="color:#f92672">+</span> Integer.<span style="color:#a6e22e">parseInt</span>(number.<span style="color:#a6e22e">toString</span>()); <span style="color:#75715e">// add number to sum</span>
+</span></span><span style="display:flex;"><span>            }
+</span></span><span style="display:flex;"><span>        }
+</span></span><span style="display:flex;"><span>
+</span></span><span style="display:flex;"><span>        System.<span style="color:#a6e22e">out</span>.<span style="color:#a6e22e">println</span>(sum);
+</span></span><span style="display:flex;"><span>    }
+</span></span><span style="display:flex;"><span>}</span></span></code></pre></div></div><div class="hextra-code-copy-btn-container hx:opacity-0 hx:transition hx:group-hover/code:opacity-100 hx:flex hx:gap-1 hx:absolute hx:m-[11px] hx:right-0 hx:top-0">
+  <button
+    class="hextra-code-copy-btn hx:group/copybtn hx:cursor-pointer hx:transition-all hx:active:opacity-50 hx:bg-primary-700/5 hx:border hx:border-black/5 hx:text-gray-600 hx:hover:text-gray-900 hx:rounded-md hx:p-1.5 hx:dark:bg-primary-300/10 hx:dark:border-white/10 hx:dark:text-gray-400 hx:dark:hover:text-gray-50"
+    title="Copy code"
+  >
+    <div class="hextra-copy-icon hx:group-[.copied]/copybtn:hidden hx:pointer-events-none hx:h-4 hx:w-4"></div>
+<div class="hextra-success-icon hx:hidden hx:group-[.copied]/copybtn:block hx:pointer-events-none hx:h-4 hx:w-4"></div>
+  </button>
+</div>
+</div>
+<div class="hx:overflow-x-auto hx:mt-6 hx:flex hx:flex-col hx:rounded-lg hx:border hx:py-4 hx:px-4 hx:border-gray-200 hx:contrast-more:border-current hx:contrast-more:dark:border-current hx:border-purple-200 hx:bg-purple-100 hx:text-purple-900 hx:dark:border-purple-200/30 hx:dark:bg-purple-900/30 hx:dark:text-purple-200">
+  <p class="hx:flex hx:items-center hx:font-medium"><svg height=16px class="hx:inline-block hx:align-middle hx:mr-2" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor" aria-hidden="true"><path stroke-linecap="round" stroke-linejoin="round" d="M13 16h-1v-4h-1m1-4h.01M21 12a9 9 0 11-18 0 9 9 0 0118 0z"/></svg>Important</p>
+
+  <div class="hx:w-full hx:min-w-0 hx:leading-7">
+    <div class="hx:mt-6 hx:leading-7 hx:first:mt-0"><p>Note, that we can&rsquo;t just do <code>Integer.parseInt()</code></p></div>
+  </div>
+</div>
 
         </div>
         <div class="hx:mt-16"></div>