I found a lot of questions about comparing objects in Java. Primitive types we can compare using == for example int
int i1 = 0;
int i2 = 0;
int i3 = 1000;
int i4 = 1000;
int i5 = 1;
int i6 = 2;
System.out.println(i1 == i2);
System.out.println(i3 == i4);
System.out.println(i5 == i6);
output is
true
true
false
When we want to compare Integer objects we can do it in two ways
equals()
and here we are comparing values
Integer i1 = 0;
Integer i2 = 0;
Integer i3 = 1000;
Integer i4 = 1000;
Integer i5 = 1;
Integer i6 = 2;
System.out.println(i1.equals(i2));
System.out.println(i3.equals(i4));
System.out.println(i5.equals(i6));
output is
true
true
false
or we can use == which compares references.
Let's take two String variables with the same value
String s1 = "Yes, this is dog";
String s2 = "Yes, this is dog";
System.out.println(s1 == s2);
System.out.println(s1.equals(s2));
It is well-known that results of both comparisons will be true
true
true
So now, I want to do this same with Integer objects. I run this piece of code
Integer i1 = 0;
Integer i2 = 0;
Integer i3 = 1000;
Integer i4 = 1000;
Integer i5 = 1;
Integer i6 = 2;
System.out.println(i1 == i2);
System.out.println(i3 == i4);
System.out.println(i5 == i6);
and the output is
true
false
false
We can meet this kind of behavior for Integer objects with these values: [-128,127]
for (int i = -129;i <129;i++) {
Integer i1 = i;
Integer i2 = i;
System.out.println(i1 == i2);
}
output:
false
true
...
false
I would like to know, what is the reason of this behavior? Does it have a big influence to performance?
In which package and in which class can I find a piece of code which takes care of this situation?
In which Java version it has been introduced and is it be maintained in Java 8?
If I want to change this behaviour, am I able to do that or I should use operator new each time?
Integer i = new Integer(1024);
Thank you in advance
