Single implementation inheritance.

JAVA PRIMER
Objects Don't Polymorph: A Conceptual View of Subtype Polymorphism

Wm. Paul Rogers
Listing 1. Single implementation inheritance.


public class Base
{
  public String m1()
  { return "Base m1"; }

  public String m2()
  { return "Base m2"; }

  public String m3()
  { return "Base m3"; }
}

public class Derived1
  extends Base
{
  public String m1()
  { return "Derived1 m1"; }

  public String m4()
  { return "Derived1 m4"; }
}

public class Derived2
  extends Derived1
{
  public String m2()
  { return "Derived2 m2"; }

  public String m5()
  { return "Derived2 m5"; }
}

// Elided
//
// Attach new Derived2 reference to new
// Derived2 object.
Derived2 derived2 = new Derived2();

// Attach new Base reference to existing
// Derived2 object.
Base base = derived2;

// Send m1 message through Derived1 and Base
// references. Object mapping to class method
// is unaffected by reference type.
derived2.m1();           // "Derived1 m1"
base.m1();               // "Derived1 m1"

// Send m2 message through Base reference.
// Derived2 object mapping is used.
base.m2();                 // "Derived2 m2"

// Attach Base reference to new Derived1 object
base = new Derived1();

// Send m1 & m2 message through Base reference.
// Now using Derived1 mappings.
base.m1();                 // "Derived1 m1"
base.m2();                 // "Base m2"

// Attach Base reference to new Base object
base = new Base();

// Send m1 & m2 message through Base reference.
// Now using Base mappings.
base.m1();	// "Base m1"
base.m2();	// "Base m2"

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