BAEL-5559 - Swap two variables using Java (#12113)

* BAEL-5559 - Swap two variables using Java

initial commit

* Updating tests names

Co-authored-by: HARDEMAN Sebastien <sebastien.hardeman@groupe-mma.fr>

core-java-modules/core-java-lang-math-3/src/test/java/com/baeldung/math/swap/SwappingVariablesUnitTest.java

@@ -0,0 +1,157 @@
+package com.baeldung.math.swap;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class SwappingVariablesUnitTest {
+
+    @Test
+    public void givenTwoStrings_whenSwappingInMethod_thenFails() {
+        
+        String a = "a";
+        String b = "b";        
+        
+        swap(a, b);
+        
+        Assertions.assertFalse(a.equals("b"));
+        Assertions.assertFalse(b.equals("a"));
+    }
+    
+    @Test
+    public void givenTwoWrappers_whenSwappingInMethod_thenSuccess() {
+        
+        Wrapper a = new Wrapper("a");
+        Wrapper b = new Wrapper("b");        
+        
+        swap(a, b);
+        
+        Assertions.assertTrue(a.string.equals("b"));
+        Assertions.assertTrue(b.string.equals("a"));
+    }
+    
+    @Test
+    public void givenTwoIntegers_whenSwappingUsingAdditionSubstraction_thenSuccess() {
+        
+        int a = 5;
+        int b = 10;              
+            
+        a = a + b;
+        b = a - b;
+        a = a - b;
+                
+        Assertions.assertTrue(a == 10);
+        Assertions.assertTrue(b == 5);
+    }
+    
+    @Test
+    public void givenTwoIntegers_whenSwappingUsingMultiplicationDivision_thenSuccess() {
+        
+        int a = 5;
+        int b = 10;              
+            
+        a = a * b;
+        b = a / b;
+        a = a / b;
+                
+        Assertions.assertTrue(a == 10);
+        Assertions.assertTrue(b == 5);
+    }
+    
+    @Test
+    public void givenTwoIntegers_whenSwappingWithOverflow_thenFails() {
+        
+        int a = Integer.MAX_VALUE;
+        int b = 10;
+                
+        a = a * b;
+        b = a / b;
+        a = a / b;
+        
+        Assertions.assertTrue(a == 10);
+        Assertions.assertFalse(b == Integer.MAX_VALUE);
+    }
+    
+    @Test
+    public void givenTwoChars_whenSwappingWithCast_thenSuccess() {
+        
+        char a = 'a';
+        char b = 'b';
+                
+        a = (char)(a * b);
+        b = (char)(a / b);
+        a = (char)(a / b);
+        
+        Assertions.assertTrue(a == 'b');
+        Assertions.assertTrue(b == 'a');
+    }
+    
+    @Test
+    public void givenTwoIntegers_whenSwappingUsingXor_thenSuccess() {
+        
+        int a = 5;
+        int b = 10;
+                
+        a = a ^ b;  
+        b = a ^ b;
+        a = a ^ b;
+        
+        Assertions.assertTrue(a == 10);
+        Assertions.assertTrue(b == 5);
+    }
+    
+    @Test
+    public void givenTwoIntegers_whenSwappingUsingSingleLineXor_thenSuccess() {
+        
+        int a = 5;
+        int b = 10;
+                
+        a = a ^ b ^ (b = a);
+        
+        Assertions.assertTrue(a == 10);
+        Assertions.assertTrue(b == 5);
+    }
+    
+    @Test
+    public void givenTwoIntegers_whenSwappingUsingAdditionSubstractionSingleLine_thenSuccess() {
+        
+        int a = 5;
+        int b = 10;
+                
+        b = (a + b) - (a = b);
+        
+        Assertions.assertTrue(a == 10);
+        Assertions.assertTrue(b == 5);
+    }
+    
+    /**
+     * Illustrates that swapping in a method doesn't work
+     */
+    private void swap(String a, String b) {
+                
+        String temp = b;
+        b = a;
+        a = temp;
+    }
+    
+    /**
+     * Illustrates swapping in a method with Wrapper class
+     */
+    private void swap(Wrapper a, Wrapper b) {
+        
+        String temp = b.string;
+        b.string = a.string;
+        a.string = temp;        
+    }
+
+    class Wrapper {
+        
+        public String string;
+
+        public Wrapper(String string) {
+            
+            this.string = string;
+        }
+        
+        
+    }
+}