设计模式-装饰者模式

1、装饰器模式

允许向一个现有的对象添加新的功能，同时又不改变其结构。

• 抽象对象

public interface Hero {
	  void learnSkills();
}

• 某类对象

class BlindMonk implements Hero {
	  private String name;
	  public BlindMonk(String name) {
	      this.name = name;
	  }
	  @Override
	  public void learnSkills() {
	      System.out.println(name + "学习了以上技能！");
	  }
}

• 抽象对象具有操作及装饰

//Decorator 技能栏:装饰类
class Skills implements Hero{
  //持有一个英雄对象接口
  private Hero hero;  
  public Skills(Hero hero) {
      this.hero = hero;
  }
  @Override
  public void learnSkills() {
      if(hero != null)
          hero.learnSkills();
  }    
}

//ConreteDecorator 技能：R
class Skill_R extends Skills{    
  private String skillName;
  public Skill_R(Hero hero,String skillName) {
	  //装饰父类对象
      super(hero);
      this.skillName = skillName;
  } 
  @Override
  public void learnSkills() {
      System.out.println("学习了技能R:" +skillName );
      //装饰父类方法
      super.learnSkills();
  }
}

• 测试

public class Test1{
  public static void main(String[] args) {
      Hero hero = new BlindMonk("李青");
      Skills skills = new Skills(hero);
      Skills r = new Skill_R(skills,"猛龙摆尾");   
      r.learnSkills();
  }
}

2、 单例模式

• 懒汉式，非线程安全

public class Singleton {
	private static Singleton instance;  
    private Singleton (){}  
    public static Singleton getInstance() {  
	    if (instance == null) {  
	        instance = new Singleton();  
	    }  
	    return instance;  
    }  
}

• 懒汉式, 线程安全

public class Singleton {  
    private static Singleton instance;  
    private Singleton (){}  
    public static synchronized Singleton getInstance() {  
	    if (instance == null) {  
	        instance = new Singleton();  
	    }  
	    return instance;  
    }  
}

• 饿汉式

public class Singleton {  
    private static Singleton instance = new Singleton();  
    private Singleton (){}  
    public static Singleton getInstance() {  
    	return instance;  
    }  
}

• 双重校验锁

public class Singleton {  
    private volatile static Singleton singleton;  
    private Singleton (){}  
    public static Singleton getSingleton() {  
	    if (singleton == null) {  
	        synchronized (Singleton.class) {  
		        if (singleton == null) {  
		            singleton = new Singleton();  
		        }  
	        }  
	    }  
	    return singleton;  
    }  
}

• 静态内部类

public class Singleton {  
    private static class SingletonHolder {  
    	private static final Singleton INSTANCE = new Singleton();  
    }  
    private Singleton (){}  
    public static final Singleton getInstance() {  
    	return SingletonHolder.INSTANCE;  
    }  
}