Wrapper Problem

[Micheal John]

package com;
 
class Example{
 public static void main(String args[]){
   Integer i1 = 1000;
   Integer i2 = 1000;
 
   Integer i3 = 10;
   Integer i4 = 10;
 
   if(i1 != i2){
     System.out.println("Not Equal");
   }
 
   if(i3 == i4){
  System.out.println("Equal");
   }
 
 }
}

I got the output as :
Not Equal
Equal

Why this difference? can anyone tell this?

[Petrus Pelser]

Wrappers of the integral types will be equal (by using ==) when they are of the same type and the value is smaller than or equal to 127.

[Satish Kota]

i1,i2 will point to same reference. Because JVM maintains a constant pool for wrapper objects just like it does for Strings. Hence i1 and i2 will point to the same reference in the constant pool. And i3,i4 will point to the same memory in the constant pool

so i1!=i2 will be False;
and i3==i4 will be True

[Sanjeev Singh]

John,
The explantaion of this quesion is very well described in K&B book.
May be you can get some clue for this problem in this code.

public static Integer valueOf(int i) {
final int offset = 128;
if (i >= -128 && i <= 127) { // must cache 
    return IntegerCache.cache[i + offset];
}
        return new Integer(i);
    }

[Joe San]

Till 127, it returns true...and beyond that, false. One exception to this is, when you say Integer i1 = new Integer(10); and Integer i2 = new Integer(10); will point to 2 different objects.

[Satish Kota]

Sanjeev,
That range of -128 to 127 is applicable to Byte, Short and Integer. Then what is the valid range for Long?
And also please let me know how did you get access to the code of Integer.valueOf() method ?

[Satish Kota]

I just downloaded JDK 1.5 Source code from Sun site. When i peeped into the Byte, Short, Integer, Long source code the range was -128 to 127

For Character the range is for anything less than <=127

But for Float, Double no caching is provided.
That is

Float f1=3.0F;
Float f2=3.0F;
System.out.println(f1==f2);
will produce false