Question

class A {
    String s = "abc";
}

class B {
    String s = "abc";

     static public void main(String[]args ) {
            A a = new A();
            B b = new B();
            System.out.println("a.s==b.s : " + (a.s==b.s));
     }
}

The output:

a.s==b.s : true

If the literal is written to the “constant pool” part of the classfile,how come 2 literals(the same contents) in 2 classes use the same interned string? How does the compiler link them together?

Answer 1

There’s a string pool into which all interned String objects go. It’s effectively a HashMap<String>. Note that the String.intern() method returns a String; the implementation is essentially

if (stringPool.contains(this))
    return stringPool.get(this);
else {
    stringPool.put(this, this);
    return this;
}

When a String object is creating while loading a class, it’s replaced by the result of calling intern(), which has the result of sharing like instances among all classes.