Wrapper Classes Autoboxing Concept

[Sahil Kapoor]

 class Scjp {
 
  public static void main(String[] args) {
      Integer i1 = 1000;
      Integer i2 = 1000;
      Long l3 = new Long("1000");
      
      if(i1 !=i2) System.out.println("Different Objects");
      if(i1 ==i2) System.out.println("Same Objects");
     
      if(i1.equals(i2))  System.out.println("Meaningfully Equivalent Objects");
      
      if(i1.equals(l3))  System.out.println("Meaningfully Equivalent Objects");
      
     
      
      Integer i3 = Integer.valueOf(12);
      Integer i4 = new Integer("12");
      
      if(i3 !=i4) System.out.println("Different Objects");
      if(i3==i4) System.out.println("Same Objects");
      
      Integer i5 = 12;
      Integer i6 = 12;
      
      if(i6 !=i5) System.out.println("Different Objects");
      if(i5==i6) System.out.println("Same Objects");
  }

}

Output :

Different Objects
Meaningfully Equivalent Objects
Different Objects
Same Objects


Please Explain !!! < I think it is flaw in JAVA >

Take care
Cheers!!!

[mohammad shaid]

Integer i3 = Integer.valueOf(12);
Integer i4 = new Integer("12");

i4 is created using new operator and so when you compare it with other wrappers they are not same(meaning they are different)

with new operator you are constructing a new object so with new opeartor you will be creating new objects which will not be the same even if those 2 objects are constructed to hold same primitive values.. Do trial and error method while coding;; you will get to know..

but i5 and i6 are same as (check K&B for assistance)

i am just a learner ;; i hope you get a better view of this concept from experts;;;

[Sridhar Gudipalli]

Here is the explanation from K&B book (Chapter#3)

In order to save memory, two instances of the following wrapper objects will always be == when their primitive values are the same:
Boolean
Byte
Character from \u0000 to \u007f (7f is 127 in decimal)
Short and Integer from -128 to 127

 
public class AutoBoxDemo {
	public static void main(String[] args) {
		Integer a = 10;
		Integer b = 10;
		System.out.println((a==b)+" : "+(a.equals(b)));
		
		Integer c = new Integer(20);
		Integer d = new Integer(20);
		System.out.println((c==d)+" : "+(c.equals(d)));
	}
}

Output:
true : true
false : true