question on equals() method

The .equals() method for the String class compares the actual value stored in the variables as opposed to object references. Below is some simple code to show how using the '==' operator can give incorrect results. The code takes 4 string variables, all holding the value "test", and compares them against the first one. You will see that it will results false on one of the Boolean checks even though they are all the same.

public static void main(String[] args) throws IOException {
   String a = "test";
   String b = "test";
   String c = a;
   String d = new String("test");

   // these test references, which means objects address in the computer's memory
   System.out.println("Testing variable \'a\' == \'b\': " + (a == b));
   System.out.println("Testing variable \'a\' == \'c\': " + (a == c));
   System.out.println("Testing variable \'a\' == \'d\': " + (a == d));

   /* Just for fun you can see this line outputs something completely different.
   This is because it adds the first string (inside the parentheses) to 'a' before
   the boolean check with b. Mathematical order of operations rules do apply.
   The '+' operator has a higher precedence than the '==' operator.
   */
   System.out.println("Testing variable \'a\' == \'b\': " + a == b);
}