What is variable shadowing used for in a Java class?

Question

I'm reading my Deitel, Java How to Program book and came across the term shadowing. If shadowing is allowed, what situation or what purpose is there for it in a Java class?

Example:

public class Foo {

    int x = 5;

    public void useField() {
        System.out.println(this.x);
    }
    public void useLocal() {
        int x = 10;
        System.out.println(x);
    }
}

Answer 1

The basic purpose of shadowing is to decouple the local code from the surrounding class. If it wasn't available, then consider the following case.

A Class Foo in an API is released. In your code you subclass it, and in your subclass use a variable called bar. Then Foo releases an update and adds a protected variable called Bar to its class.

Now your class won't run because of a conflict you could not anticipate.

However, don't do this on purpose. Only let this happen when you really don't care about what is happening outside the scope.