Difference in results for JDK 1.4 And 1.5

[Nabila Mohammad]

 public class HelloWorld
{
 
public static void main(String[] args)

{
Integer i1=1000;
Integer i2=1000;
 
if(i1==i2)
System.out.println("i1==i2 is true");
 
if(i1.equals(i2))
System.out.println("12 is equal to i2");
 
}
}
 
   

I ran this program in both JDK1.4 and JDK1.5

In JDK1.4 I got an error.
Incompatible type.
Found int required java.lang.Integer.

However it ran with out errors in JDK1.5.

Can some one tell me the difference.
I thought both of them had wrapper classes.

[Jesper de Jong]

Yes, wrapper classes exist in both Java 1.4 and Java 5, but autoboxing is a new feature of Java 5.

This does not compile on Java 1.4:

Integer i = 1000;

For Java 1.4, you'll have to write:

Integer i = Integer.valueOf(1000);

[Nabila Mohammad]

Thanks.
I think I still have doubts on that, but will study and let you know if there is anything I need to understand.Still weak on the concepts of Autoboxing.

Take Care.

[Nabila Mohammad]

I have a question..

When i declare an instance of a wrapper class, does it creat an object on the heap?
And if yes, how is the object being created with out using "new".


Eg.

Integer i2=177;

I know that int value 177 is being Autoboxed to Integer type.

[marc weber]

Yes, whether created with "new" or with autoboxing, an Integer instance is an object on the heap. You don't need to say "new" because autoboxing automatically takes care of instantiating the object for you.

But one important difference is that autoboxing will not always create a new object. If the value is within the range of a byte (-128 to 127), then the boxed instances are "pooled." If the "pool" already contains a wrapped instance of that value, then autoboxing will return a reference to the pooled instance instead of creating a new object.

[Nabila Mohammad]

Thanks.
Can you please clear me about the concept of pooliing.
From what I gathered, Pooling is used to save memory and instead of creating a new object it looks for an object with the same value and creates a reference to it instead of creating a new one.
But what happens if there are no objects of that kind on the heap?
And what exactly do you mean by having and object on the pool.