added java weird example and documentation

Author: Juraj Veverka

README.md

@@ -41,6 +41,7 @@ gradle --build-file di-examples/build.gradle clean test
 * [ssh server demo](ssh-server-demo)
 * [JCE demo](jce-demo)
 * [com.fasterxml.jackson](jackson-fasterxml-demo)
+* [weird java stuff](java-is-weird)
 * __Databases__
   * [mongodb demo](mongodb-demo)
   * [hibernate demo](hibernate-demo)

java-is-weird/README.md

@@ -0,0 +1,12 @@
+# Examples of weird Java stuff :)
+
+* [testBigDecimalCompare](src/test/java/itx/examples/javaisweird/tests/WeirdTesting) -
+  BigDecimal.equals(?) compares content of objects, however BigDecimal.compare(?) deliberately considers values like '1' and '1.0' as same value.
+* [testIntegerCompare](src/test/java/itx/examples/javaisweird/tests/WeirdTesting) -
+  The Integer type keeps a cache of all objects with a value in the range of -128 to 127 for performance reasons. So when you declare new variables in that range, you’re actually referring to the same object. 
+* [testCharArithmetic](src/test/java/itx/examples/javaisweird/tests/WeirdTesting) -
+  ```
+  char ch = '0'; // ASCII for ‘0’ is 48
+  ch *= 1.1; // 48 x 1.1 is 52.8 which turns to 52 when cast to char
+  assertEquals('4', ch); // 52 represents ‘4’ in ASCII
+  ```

java-is-weird/src/test/java/itx/examples/javaisweird/tests/WeirdTesting.java

@@ -18,16 +18,23 @@ public void testBigDecimalCompare() {
 
     @Test
     public void testIntegerCompare() {
-        Integer a = 100;
-        Integer b = 100;
+        Integer a = 42;
+        Integer b = 42;
 
-        Integer c = 200;
-        Integer d = 200;
+        Integer c = 666;
+        Integer d = 666;
 
         assertTrue(a == b);
         assertEquals(a, b);
         assertFalse(c == d);
         assertEquals(c, d);
     }
 
+    @Test
+    public void testCharArithmetic() {
+        char ch = '0';
+        ch *= 1.1;
+        assertEquals('4', ch);
+    }
+
 }