Bruce Eckel's Thinking in Java Contents | Prev | Next

protected

Now that you’ve been introduced to inheritance, the keyword protected finally has meaning. In an ideal world, private members would always be hard-and-fast private, but in real projects there are times when you want to make something hidden from the world at large and yet allow access for members of derived classes. The protected keyword is a nod to pragmatism. It says “This is private as far as the class user is concerned, but available to anyone who inherits from this class or anyone else in the same package.” That is, protected in Java is automatically “friendly.”

The best tack to take is to leave the data members private – you should always preserve your right to change the underlying implementation. You can then allow controlled access to inheritors of your class through protected methods:

//: Orc.java
// The protected keyword
import java.util.*;

class Villain {
  private int i;
  protected int read() { return i; }
  protected void set(int ii) { i = ii; }
  public Villain(int ii) { i = ii; }
  public int value(int m) { return m*i; }
}

public class Orc extends Villain {
  private int j;
  public Orc(int jj) { super(jj); j = jj; }
  public void change(int x) { set(x); }
} ///:~

You can see that change( ) has access to set( ) because it’s protected.

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