class SwordsMan{ private String name; public SwordsMan(String userName){ name = userName; } public void run(){ System.out.println(name + " "); } public void fight(){ System.out.println(name + " "); } } 

 class Magician { private String name; public Magician(String userName){ name = userName; } public void run(){ System.out.println(name + " "); } public void fight(){ System.out.println(name + " "); } } 

 class Character{ protected String name; public Character(String userName){ name = userName; } protected void run(){ System.out.println(name +" 跑走"); } public void fight(){} } 

 class SwordsMan extends Character{ public SwordsMan(String username){ super(username); } public void fight(){ System.out.println(name + " "); } } class Magician extends Character{ public Magician(String username){ super(username); } public void fight(){ System.out.println(name + " "); } } 

 interface FightMethod{ public void fight(String name); } 

 class UseSword implements FightMethod{ public void fight(String name){ System.out.println(name + " "); } } 

Then changed so that the Swordsman class

 class SwordsMan extends Character{ private UseSword charUseSword; public SwordsMan(String username){ super(username); charUseSword = new UseSword(); charUseSword.fight(username); } } 

Like this very problem! Problem?

Recall just happened here, so that each role must declare an attack object,
And entities to it, the 100 roles still need to configure the 100 entities,
You will be exhausted ...

How should we do?

Polymorphism is in this place such a declaration

 FightMethod fm = new UseSword(); fm.fight(); FightMethod fm是形式型態的宣告,而new UseSword()才是你實際型態的宣告。 

Polymorphism (Polymorphism) when the actual type of a variable (actual type) and form type
(Formal type) is inconsistent with the method call this variable will call the "correct" version.
That is, the version of the actual type.

Therefore, we can thus directly in the Character class so declared

 class Character{ public String name; protected FightMethod fm; public Character(String userName){ name = userName; } public void run(){ System.out.println(name +" "); } protected void useWeapon(){ fm.fight(name); } } 

In SwordsMan within such declared

 class SwordsMan extends Character{ public SwordsMan(String username){ super(username); fm = new UseSword(); } } 

So the swordsman want to change the attack can be directly replaced by useKnife ();
Or to an increase of one hundred roles, can also increase the attack on the interface.

Complete code

  class Character {
     protected String name;
 protected FightMethod fm;
 public Character (String userName) {
 name = userName;
 }
 public void run () {
 System.out.println (name + "run away");
 }
 protected void useWeapon () {
 fm.fight (name);
 }
 }
 interface FightMethod {
 public void fight (String name);
 }
 class UseSword implements FightMethod {
 public void fight (String name) {
 System.out.println (name + "waving the sword");
 }
 }
 class UseMagic implements FightMethod {
     public void fight (String name) {
         System.out.println (name + "magic");
     }
 }
 class SwordsMan extends Character {
 public SwordsMan (String username) {
 super (username);
 fm = new UseSword ();
 }

 }
 class Magician extends Character {
 public Magician (String username) {
 super (username);
 fm = new UseMagic ();
 }

 }
 class TestJava { 
     public static void main (String [] args) {
         SwordsMan swordMan = new SwordsMan ("John");
         Magician magician = new Magician ("Mary");
         swordMan.run ();
         magician.useWeapon ();
         swordMan.useWeapon ();
     }
 }

Is a magician or a swordsman will automatically correspond to the corresponding

 John  

Do you see that the multi-benefits of it?

Code download
http://uploadingit.com/file/hy2pfypcshgyp8c3/StrategyPatternDemo.zip