java 在观察者模式中使用泛型T的实例

被观察者

public class Observable {

  List observers = new ArrayList();

  boolean changed = false;


  
  public void addObserver(Observer observer) {
    if (observer == null) {
      throw new NullPointerException("observer == null");
    }
    synchronized (this) {
      if (!observers.contains(observer))
 observers.add(observer);
    }
  }

  
  protected void clearChanged() {
    changed = false;
  }

  
  public int countObservers() {
    return observers.size();
  }

  
  public synchronized void deleteObserver(java.util.Observer observer) {
    observers.remove(observer);
  }

  
  public synchronized void deleteObservers() {
    observers.clear();
  }

  
  public boolean hasChanged() {
    return changed;
  }

  
  public void notifyObservers() {
    notifyObservers(null);
  }

  
  public void notifyObservers(T data) {
    int size = 0;
    Observer[] arrays = null;
    synchronized (this) {
      if (hasChanged()) {
 clearChanged();
 size = observers.size();
 arrays = new Observer[size];
 observers.toArray(arrays);
      }
    }
    if (arrays != null) {
      for (Observer observer : arrays) {
 observer.update(this, data);
      }
    }
  }

  
  protected void setChanged() {
    changed = true;
  }
}

观察者

public interface Observer {
  public void update(Observable observable, T data);
}

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