Java/Class/Override Polymorphism

It only looks like you can override a private or private final method

// : c06:FinalOverridingIllusion.java
// It only looks like you can override a private or private final method.
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
class WithFinals {
  // Identical to "private" alone:
  private final void f() {
    System.out.println("WithFinals.f()");
  }
  // Also automatically "final":
  private void g() {
    System.out.println("WithFinals.g()");
  }
}
class OverridingPrivate extends WithFinals {
  private final void f() {
    System.out.println("OverridingPrivate.f()");
  }
  private void g() {
    System.out.println("OverridingPrivate.g()");
  }
}
class OverridingPrivate2 extends OverridingPrivate {
  public final void f() {
    System.out.println("OverridingPrivate2.f()");
  }
  public void g() {
    System.out.println("OverridingPrivate2.g()");
  }
}
public class FinalOverridingIllusion {
  public static void main(String[] args) {
    OverridingPrivate2 op2 = new OverridingPrivate2();
    op2.f();
    op2.g();
    // You can upcast:
    OverridingPrivate op = op2;
    // But you can"t call the methods:
    //! op.f();
    //! op.g();
    // Same here:
    WithFinals wf = op2;
    //! wf.f();
    //! wf.g();
  }
} ///:~

Method override demo

/* From http://java.sun.ru/docs/books/tutorial/index.html */
/*
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 *  and/or other materials provided with the distribution.
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 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MIDROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
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public class Earth extends Planet {
    public static void hide() {
        System.out.println("The hide method in Earth.");
    }
    public void override() {
        System.out.println("The override method in Earth.");
    }
    public static void main(String[] args) {
        Earth myEarth = new Earth();
        Planet myPlanet = (Planet)myEarth;
        myPlanet.hide();                   
        myPlanet.override();
    }
}
class Planet {
    public static void hide() {
        System.out.println("The hide method in Planet.");
    }
    public void override() {
        System.out.println("The override method in Planet.");
    }
}

Override Shape

// : c10:Shapes.java
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
class Shape {
  void draw() {
    System.out.println(this + ".draw()");
  }
}
class Circle extends Shape {
  public String toString() {
    return "Circle";
  }
}
class Square extends Shape {
  public String toString() {
    return "Square";
  }
}
class Triangle extends Shape {
  public String toString() {
    return "Triangle";
  }
}
public class Shapes {
  public static void main(String[] args) {
    // Array of Object, not Shape:
    Object[] shapeList = { new Circle(), new Square(), new Triangle() };
    for (int i = 0; i < shapeList.length; i++)
      ((Shape) shapeList[i]).draw(); // Must cast
  }
} ///:~

Polymorphism in Java

// : c07:Shapes.java
// Polymorphism in Java.
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
import java.util.Random;
class Shape {
  void draw() {
  }
  void erase() {
  }
}
class Circle extends Shape {
  void draw() {
    System.out.println("Circle.draw()");
  }
  void erase() {
    System.out.println("Circle.erase()");
  }
}
class Square extends Shape {
  void draw() {
    System.out.println("Square.draw()");
  }
  void erase() {
    System.out.println("Square.erase()");
  }
}
class Triangle extends Shape {
  void draw() {
    System.out.println("Triangle.draw()");
  }
  void erase() {
    System.out.println("Triangle.erase()");
  }
}
// A "factory" that randomly creates shapes:
class RandomShapeGenerator {
  private Random rand = new Random();
  public Shape next() {
    switch (rand.nextInt(3)) {
    default:
    case 0:
      return new Circle();
    case 1:
      return new Square();
    case 2:
      return new Triangle();
    }
  }
}
public class ShapesDemo {
  private static RandomShapeGenerator gen = new RandomShapeGenerator();
  public static void main(String[] args) {
    Shape[] s = new Shape[9];
    // Fill up the array with shapes:
    for (int i = 0; i < s.length; i++)
      s[i] = gen.next();
    // Make polymorphic method calls:
    for (int i = 0; i < s.length; i++)
      s[i].draw();
  }
} ///:~