CODEWITHSUNDEEP
java
Wizard
Wizard

Reputation: 22113

new Integer(1) returns a different id with 1

Suppose the following assignment:

jshell> int a = 1;
a ==> 1
jshell> int b = 1;
b ==> 1
jshell> var c = new Integer(1);
c ==> 1

Check their id with System.identityHashCode:

jshell> System.out.println(System.identityHashCode(1))
1938056729

jshell> System.out.println(System.identityHashCode(a))
1938056729

jshell> System.out.println(System.identityHashCode(b))
1938056729

jshell> System.out.println(System.identityHashCode(c))
343965883

C returns a different ID, the "1" which c references is different from that of a and b?

Upvotes: 1

Views: 67

Answers (1)

Juan C Nuno
Juan C Nuno

Reputation: 563

That is expected. The first three lines are boxing conversions and Integer::valueOf is specified to return the same instances for the inclusive range -128 to 127.

You explicitly used new for c. That will always create a new instance which returns a different hash code. If you replace new Integer(1) with Integer.valueOf(1) it will return the same hash code as the others.

Upvotes: 3

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