Question

I am reading the book Java Concurrency in Practice.
In Chapter 4.2 – Instance Confinement it says Confined objects can also escape by publishing others such as iterators or innerclass instances that may indirectly publish the confined objects.
Can someone give an example (code) on each please ?

Answer 1

Sure, here are two examples.
Iterator:

public class NonSafe {
    private List x;

    public Iterator getIterator() {
        return x.iterator();
    }
}

Even though x is private, you can still perform operations, such as delete(), on its Iterator, modifying x.

Inner class:

public class Outer {
    private Object x;

    class Inner {
        public Object lookAtOuter() {
            return Outer.this.x;
        }
    }
}

Here, an escaped reference to Inner, causes an indirect reference to x to leak out, even though it is private.