As we know that == in case of Objects returns true if pointing to the same reference else it returns false.
So , if i have taken
Integer a = new Integer("1"); // Creating Integer Object a
Integer b = new Integer("1"); // Creating Integer Object b
and then perform a == b , then it returns true but they both have different references.
The JVM caches integer values between -127 to 127.
That's the reason == works for Integer value between this range.
But:
Integer i1=new Integer("11");
Integer i2=new Integer("11");
System.out.println(i1==i2); //false
Integer i3=11;
Integer i4=11;
System.out.println(i3==i4); //true
Integer i5=128;
Integer i6=128;
System.out.println(i5==i6); //false
new keyword, a new object has to be created and returned. Caches don't work in that case.
Because it is overridden. source:
public boolean equals(Object obj) {
if (obj instanceof Integer) {
return value == ((Integer)obj).intValue();
}
return false;
}
Let me more elaborate on this, @asAmit Bhati said in his answer when we write
Integer i1=new Integer("11");
Integer i2=new Integer("11");
System.out.println(i1==i2); //false
jvm creates two separate objects and comparing them with "==" results in false. but when we write the following code:
Integer i3=11;
Integer i4=11;
System.out.println(i3==i4); //true
it will be translated into this:
Integer i3=Integer.valueOf(11);
Integer i4=Integer.valueOf(11);
Implementation of valueOf method is as follow(in java 1.8):
public static Integer valueOf(int var0) {
return var0 >= -128 && var0 <= Integer.IntegerCache.high?Integer.IntegerCache.cache[var0 + 128]:new Integer(var0);
}
as you can see if the value is between -128 and Maximum cache value (which can be configured using this jvm parameter -Djava.lang.Integer.IntegerCache.high), it will retrieve the cached value and doesn't create a new instance of Integer that is why (==) returns true for certain values!
also note that the same goes for Character Wrapper class but not for Float and Double classes.
As the answer above says, it may work in many cases, nevertheless you shouldn't compare two Integer with == since it may present problems in some cases.
Check this answer for more information:
If you check equals method implementation in Integer class it is:
public boolean equals(Object obj) {
if (obj instanceof Integer) {
return value == ((Integer)obj).intValue();
}
return false;
}
From here you can see it uses "==" operator.
Now the reason behind it. Ultimately you have to compare value of the Integer wrapper class, which will happen automatically because of autoboxing and unboxing in Java.
And also from the method definition you can see that it is retrieving passed Object value using ((Integer)obj).intValue().
true?