first commit

java/expression/exceptions/CheckedSubtract.java

@@ -0,0 +1,31 @@
+package expression.exceptions;
+
+import expression.AbstractBinaryOperation;
+import expression.AbstractExpression;
+import expression.OverflowException;
+
+import java.math.BigDecimal;
+import java.math.BigInteger;
+
+/**
+ * @author Doschennikov Nikita (me@fymio.us)
+ */
+public class CheckedSubtract extends AbstractBinaryOperation {
+    public CheckedSubtract(AbstractExpression l, AbstractExpression r) { super(l, r); }
+
+    @Override protected String  getOperator()  { return "-"; }
+    @Override protected int     getPriority()  { return 1; }
+    @Override protected boolean isRightAssoc() { return true; }
+
+    @Override
+    protected int applyInt(int a, int b) {
+        int result = a - b;
+        if (((a ^ b) & (a ^ result)) < 0) {
+            throw new OverflowException("subtraction");
+        }
+        return result;
+    }
+
+    @Override protected BigInteger applyBi(BigInteger a, BigInteger b) { return a.subtract(b); }
+    @Override protected BigDecimal applyBd(BigDecimal a, BigDecimal b) { return a.subtract(b); }
+}