Boolean Wrappers?

[Joe Harry]

Guys,

This code below is from Dan Chisholm,

class C {
  public static void main(String[] args) {
    Boolean b1 = Boolean.valueOf(true);
    Boolean b2 = Boolean.valueOf(true);
    Boolean b3 = Boolean.valueOf("TrUe");
    Boolean b4 = Boolean.valueOf("tRuE");
    System.out.print((b1==b2) + ",");
    System.out.print((b1.booleanValue()==b2.booleanValue()) + ",");
    System.out.println(b3.equals(b4));
}}

How come it prints true for b1 == b2?? Confused.

[Vinayagar Karpagam]

I believe the catch here is the valueOf().
When two wrappers are compared with ==, the references only are compared.
b1 == b2 will be false when b1 = new Boolean(true) & b2 = new Boolean(true).
But since valueOf() is used here, it gives the same object to both b1 & b2.

Hope this helps.

[Sanjeev Singh]

All the Boolean objects (unless created with new operator)are same if there boolean value are same.So here all the references b1,b2,b3,b4 will retrun true when checked with == amongst themselfs.
The same is true for Character(ascii from 0 to 127),Interger(-128 to 127)),Short,Byte.

[Sathishkumar Ethiraju]

do you mean
Integer i1 = Integer.valueOf("1"), i2 = Integer.valueOf("1"),
i3 = Integer.valueOf("150"), i4 = Integer.valueOf("150")
System.out.println(i1==i2);
System.out.println(i3==i4);

will result in
true
false

i am getting
false
false

[Edwin Dalorzo]

The thing is that Integer.valueOf(String) always returns a new Integer while Boolean.valueOf(String) uses the constants Boolean.TRUE and Boolean.FALSE every time you invoke it.

Therefore, Boolean.valueOf(String) always returns the same object. That is not the case of Integer.valueOf(String).

Something similiar happens if you use Integer.valueOf(int), since the first 128 Integers are cached.

Integer a = Integer.valueOf(1);
Integer b = Integer.valueOf(2);
Integer c = Integer.valueOf(128);
Integer d = Integer.valueOf(128);

In this case a and b are the same object, while c and d are different objects.
[ December 21, 2006: Message edited by: Edwin Dalorzo ]