Integer Class

[souji nutak]

Can any one give explanation for the below code?

class Program {
public static void main(String[] args) {
Integer i1 = 20;
Integer i2 = 20;
Integer i3 = 201;
Integer i4 = 201;
System.out.println(i1 == i2);
System.out.println(i3 == i4);
}
}

it is giving an output

true
false

why so?

[Srinivas Kumar]

Did you try executing it or somewhere posted in the website?

[j bande]

hi souji that output is right because up to some value == results true after that limit it results false. i hope that range is int range. sorry i am not sure but that output is right no doubt about it. I am very sure because i tried in my system.
Regards,
JBande.
[ March 23, 2007: Message edited by: j bande ]

[souji nutak]

hi VSSMK,

i executed this program, it is giving the output that i wrote there. i didn't understood why it is giving true in one case and false in another

could you please explain me that in detail

[Srinivas Kumar]

I really doubt the initialization of the code
Integer i1 = 20;
Integer i2 = 20;
Integer i3 = 201;
Integer i4 = 201;

You cannot initialize an Interger wrapper object like that.There are 2 overloaded constructors.one that takes primitive int and the other that takes string.

[JB Ramesh]

class Program {
public static void main(String[] args) {
Integer i1 = 20;
Integer i2 = 20;
Integer i3 = 201;
Integer i4 = 201;
System.out.println(i1 == i2);
System.out.println(i3 == i4);
}
}

it is giving an output

true
false

why so?

You executed this code in JDK 5.0. Please refer "Boxing" concept which is a new feature in 5.0

While boxing same reference is used if the range is from -128 to 127. Thats why i1 and i2 refers same Object. i3 and i4 are more than 127. So refers different objects.

[j bande]

Consider the following code fragment:
Integer i1 = 100;
Integer i2 = 100;
Integer i3 = 1000;
Integer i4 = 1000;
System.out.println(i1==i2);
System.out.println(i3==i4);
Can you guess what will be printed on the screen? If your answer is false--well, you're wrong.
In this case, J2SE 5.0 works differently. Certain ranges of values are stored as immutable objects by
the Java Virtual Machine. So, in this case, the output is:
true
false
Normally, when the primitive types are boxed into the wrapper types, the JVM allocates memory and
creates a new object. But for some special cases, the JVM reuses the same object.
The following is the list of primitives stored as immutable objects:
� boolean values true and false
� All byte values
� short values between -128 and 127
� int values between -128 and 127
� char in the range \u0000 to \u007F


May be this you will be more clear.