What is variable shadowing used for in a Java class?

java shadowing
Jayson picture Jayson · Jul 7, 2009 · Viewed 32.5k times · Source

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

Yishai picture Yishai · Jul 7, 2009

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.

Related questions

In Java, if a child class shadows a static parent variable with an instance child variable, which variable will inherited methods use?

This is probably a bad thing to do, as discussed in Can parent and child class in Java have same instance variable?. (What if the parent variable name is changed? Then it will not be shadowed anymore.) However, I am …

Read More
How do I convert a String to an int in Java?

How can I convert a String to an int in Java? My String contains only numbers, and I want to return the number it represents. For example, given the string "1234" the result should be the number 1234.

Read More
How do I declare and initialize an array in Java?

How do I declare and initialize an array in Java?

Read More