Java Common Class Library--observer design pattern (observable class observer interface)

Original link: http://www.2cto.com/kf/201310/253013.html

If you want to implement the observer pattern, you must rely on the observable class and observer interfaces provided in the Java.util package.

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import java.util.* ;  class House extends Observable{ // 表示房子可以被观察      private float price ;// 价钱      public House(float price){          this.price = price ;      }      public float getPrice(){          return this.price ;      }      public void setPrice(float price){          // 每一次修改的时候都应该引起观察者的注意          super.setChanged() ;    // 设置变化点          super.notifyObservers(price) ;// 价格被改变          this.price = price ;      }      public String toString(){          return "房子价格为：" + this.price ;      }  };   class HousePriceObserver implements Observer{      private String name ;      public HousePriceObserver(String name){ // 设置每一个购房者的名字          this.name = name ;      }      public void update(Observable o,Object arg){          if(arg instanceof Float){              System.out.print(this.name + "观察到价格更改为：") ;              System.out.println(((Float)arg).floatValue()) ;          }      }  };  public class ObserDemo01{      public static void main(String args[]){          House h = new House(1000000) ;          HousePriceObserver hpo1 = new HousePriceObserver("购房者A") ;          HousePriceObserver hpo2 = new HousePriceObserver("购房者B") ;          HousePriceObserver hpo3 = new HousePriceObserver("购房者C") ;          h.addObserver(hpo1) ;          h.addObserver(hpo2) ;          h.addObserver(hpo3) ;          System.out.println(h) ; // 输出房子价格          h.setPrice(666666) ;    // 修改房子价格          System.out.println(h) ; // 输出房子价格      }  };

Running Result: House price is: 1000000.0 Buyers C observed price changed to: 666666.0 House Buyer B observed price changed to: 666666.0 buyer a observed price changed to: 666666.0 houses Price: 666666.0

Java Common Class Library--observer design pattern (observable class observer interface)