first commit

java/expression/exceptions/CheckedAdd.java

@@ -0,0 +1,29 @@
+package expression.exceptions;
+
+import java.math.BigDecimal;
+import java.math.BigInteger;
+
+import expression.*;
+
+/**
+ * @author Doschennikov Nikita (me@fymio.us)
+ */
+public class CheckedAdd extends AbstractBinaryOperation {
+    public CheckedAdd(AbstractExpression l, AbstractExpression r) { super(l, r); }
+
+    @Override protected String  getOperator()  { return "+"; }
+    @Override protected int     getPriority()  { return 1; }
+    @Override protected boolean isRightAssoc() { return false; }
+
+    @Override
+    protected int applyInt(int a, int b) {
+        int result = a + b;
+        if (((a ^ result) & (b ^ result)) < 0) {
+            throw new OverflowException("addition");
+        }
+        return result;
+    }
+
+    @Override protected BigInteger applyBi(BigInteger a, BigInteger b) { return a.add(b); }
+    @Override protected BigDecimal applyBd(BigDecimal a, BigDecimal b) { return a.add(b); }
+}