String equals in Java

Some remarkable samples about String equals vs == comparator in Java.
You may have different output if you use == comparator instead equals for String test.
 See sample code:


public class StringTest {

   
    public static void main (String [] args){
        testA();
       
        testB();
    }

   
    static void testA(){
        System.out.println (" testA");
        // good memory usage!!  RECOMENDED constructor
        String s1 = "a";
        String s2 = "a";
        System.out.println (" s1 = \"a\"");
        System.out.println (" s2 = \"a\"");
        if (s1 == s2 ){
            System.out.println (" s1 == s2 is true");
        } else {
            System.out.println (" s1 == s2 is false");
        }
        if (s1.equals(s2)  ){
            System.out.println (" s1.equals(s2) is true ");
        } else {
            System.out.println (" s1.equals(s2) is false ");
        }
    }
   
    static void testB(){
        System.out.println (" testB");
        // waste memory !! NOT RECOMENDED CONSTRUCTOR FOR STRINGS
        String s1 = new String ("a");
        String s2 = new String("a");
        System.out.println (" s1 = new String(\"a\")");
        System.out.println (" s2 = new String(\"a\")");
        if (s1 == s2 ){
            System.out.println (" s1 == s2");
        } else {
            System.out.println (" s1 == s2 is false");
        }
        if (s1.equals(s2)  ){
            System.out.println (" s1.equals(s2) is true ");
        } else {
            System.out.println (" s1.equals(s2) is false ");
        }
    }




   
This is code output:

 testA
 s1 = "a"
 s2 = "a"
 s1 == s2 is true
 s1.equals(s2) is true
 testB
 s1 = new String("a")
 s2 = new String("a")
 s1 == s2 is false
 s1.equals(s2) is true

 
  /**
     * Comments :
     * String offeres many constructors for Strings:
     *   in testA
     *   String s1 = "a"; create a literal "a" in pool memory ans s1 refers to it
     *   String s2 = "a"; s2 refers to same previous literal in pool.
     *  
     *   otherwise in testB     
     *    String s1 = new String("a") ;  because we use new keyword a new String object is created in not  pool memory (s1 refers to it) and  in addiction literal "a" is placed  in pool memory;
     *    String s2 = new String("a") ;  because we use new keyword a new String object is created in not  pool memory and (different from previous) s2 refers to it
     */
   
   
}