Is there such thing as boolean pool?

Question

I have two questions and unfortunately I can't find answers.

If we declare 1000 boolean variables equals to true will all of them have the same reference to true literal?

Java is pass-by-value so consider the code

public class Test {
    public static boolean global;

    public static void main(String[] args) {
        foo(false);
        System.out.println(global);
    }

    public static void foo(boolean bar) {
        global = bar;
    }
}

In foo() method the primitive value of boolean variable will be copied and it means that global will have another reference for the literal. Or will Java perform some kind of pool lookup for this and global will also reference the same memory location as argument?

The main distinction between _reference_ types and _primitive_ types is that primitive typed variables will not reference a value; they directly contain the value. That means there is no need for a pool ... — Seelenvirtuose, May 07 '18 at 08:11
Just to clarify: Java is not usually pass-by-value. Java is usually pass-by-reference, it's pass-by-value only with respect to primitive types. — Piotr Wilkin, May 07 '18 at 08:21
@PiotrWilkin Oh no. Java uses always [pass-by-value](https://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value). In case of reference typed variables the value _is_ the reference. That's it. — Seelenvirtuose, May 07 '18 at 08:25

score 3 · Accepted Answer · answered May 07 '18 at 08:13

Yes, there is a pool. But only if you use Boolean object instead of boolean primitive value and if you create it using method valueof or Boolean.TRUE/Boolean.FALSE insteand of a constructor. Check the Boolean javadoc for reference.

Also, take a look to the constructor javadoc. It says:

It is rarely appropriate to use this constructor. Unless a new instance is required, the static factory valueOf(boolean) is generally a better choice. It is likely to yield significantly better space and time performance.

Is there such thing as boolean pool?

1 Answers1