Java Puzzle – Magic of Auto-boxing

 

Auto-boxing is introduced in JDK 5.0.  it converts primitive data variable to corresponding wrapper classes and vice versa without any explicit efforts.

For example int to Integer and Integer to int.

Here is the one program using auto-boxing feature

  1: class AutoBoxingTest 
  2: { 
  3:     public static void main(String[] args) 
  4:     {    
  5:         boolean b1=true, b2=true; 
  6:         System.out.println("boolean Result  = "+ compare(b1,b2)+"\n");        
  7:         System.out.println("Int Result  = "+ compare(10,10)+"\n"); 
  8:         System.out.println("String Result  = "+ compare("ABC","ABCE")+"\n"); 
  9:         System.out.println("float Result  = "+ compare(10.00f,10f)+"\n"); 
 10:         System.out.println("Mixed Result  = "+ compare(10l,10l)+"\n"); 
 11:         System.out.println("Mixed[long,int] Result  = "+ compare(10l,10)+"\n"); 
 12:         System.out.println("Mixed[float,int] Result  = "+ compare(10.00f,10)+"\n"); 
 13:     } 
 14: 
 15:     public static boolean compare(Object obj1, Object obj2){ 
 16:         if(obj1!=null && obj2!=null){ 
 17:             System.out.println("Auto boxing class = [ "+ obj1.getClass().getName()+", " +obj2.getClass().getName()+" ]"); 
 18:             return obj1.equals(obj2); 
 19:         } 
 20:         return false; 
 21:     } 
 22: }
 23: 
 24: 

What do you think, what would be output or compilation error ?

Output :

Auto boxing class = [ java.lang.Boolean, java.lang.Boolean ]

boolean Result  = true

Auto boxing class = [ java.lang.Integer, java.lang.Integer ]

Int Result  = true

Auto boxing class = [ java.lang.String, java.lang.String ]

String Result  = false

Auto boxing class = [ java.lang.Float, java.lang.Float ]

float Result  = true

Auto boxing class = [ java.lang.Long, java.lang.Long ]

Mixed Result  = true

Auto boxing class = [ java.lang.Long, java.lang.Integer ]

Mixed[long,int] Result  = false

Auto boxing class = [ java.lang.Float, java.lang.Integer ]

Mixed[float,int] Result  = false

Output completed (0 sec consumed)