用于检测变量更改的布尔Java事件侦听器

Question

我似乎在任何地方都找不到我问题的答案。是否有任何事件侦听器可以检测布尔值或其他变量的变化，然后对其进行操作。或者是否可以创建一个自定义事件侦听器来检测此问题

请注意，我似乎在任何地方都找不到解决方案，我发现this website正在解释如何创建自定义事件

Answer 1

使用PropertyChangeSupport。您不必实现那么多，而且它是线程安全的

public class MyClassWithText {
    protected PropertyChangeSupport propertyChangeSupport;
    private String text;

    public MyClassWithText () {
        propertyChangeSupport = new PropertyChangeSupport(this);
    }

    public void setText(String text) {
        String oldText = this.text;
        this.text = text;
        propertyChangeSupport.firePropertyChange("MyTextProperty",oldText, text);
    }

    public void addPropertyChangeListener(PropertyChangeListener listener) {
        propertyChangeSupport.addPropertyChangeListener(listener);
    }
}

public class MyTextListener implements PropertyChangeListener {
    @Override
    public void propertyChange(PropertyChangeEvent event) {
        if (event.getPropertyName().equals("MyTextProperty")) {
            System.out.println(event.getNewValue().toString());
        }
    }
}

public class MyTextTest {
    public static void main(String[] args) {
        MyClassWithText interestingText = new MyClassWithText();
        MyTextListener listener = new MyTextListener();
        interestingText.addPropertyChangeListener(listener);
        interestingText.setText("FRIST!");
        interestingText.setText("it's more like when you take a car, and you...");
    }
}

Answer 2

您正在设置的布尔值只能通过setter方法执行，如：

public void setFlag(boolean flag){
    //Method code goes here
}

现在在Now set方法中，您可以根据输入的值和需要触发的事件来决定。我用简单的术语进行解释，而不引入复杂的术语，这样您可以更好地理解，所以代码片段如下所示：

public void setFlag(boolean flag){

    //if flag is TRUE do something
    //If flag is FALSE then do something 

    //And finally do what you needed to do with flag
}

如果需要更多信息，请提问

Answer 3

当您想要侦听I/O更改时，可以创建一个侦听器。主要是图形。 您的问题的答案是保持正在运行的程序的状态，然后检查变量是否从程序的无限循环内的状态更改

Answer 4

您还可以尝试实现一个观察者

首先创建可观察对象：

import java.util.Observable;

public class StringObservable extends Observable {
 private String name;


 public StringObservable(String name) {
  this.name = name;
 }

 public String getName() {
  return name;
 }


 public void setName(String name) {
  this.name = name;
  setChanged();
  notifyObservers(name);
 }

}

然后观察员：

import java.util.Observable;
import java.util.Observer;

public class NameObserver implements Observer {
 private String name;

 public NameObserver() {
  name = null;
 }

 public void update(Observable obj, Object arg) {
  if (arg instanceof String) {
   name = (String) arg;
   System.out.println("NameObserver: Name changed to " + name);
  } else {
   System.out.println("NameObserver: Some other change to subject!");
  }
 }
}

在您的主要位置（或其他任何位置）：

public class TestObservers {
 public static void main(String args[]) {

  // Create the Subject and Observers.
  StringObservable s = new StringObservable("Test");
  NameObserver nameObs = new NameObserver();

  // Add the Observer
  s.addObserver(nameObs);


  // Make changes to the Subject.
  s.setName("Test1");
  s.setName("Test2");
 }
}

大部分发现here

Answer 5

很晚才回答，但这是一个可以用Observer/Observable解决的问题Example

Answer 6

就像您需要创建一个事件侦听器一样，您也需要创建事件firer——因为没有任何自动的方法可以为您做到这一点。我提供了示例代码，向您展示了如何实现这样一个firer

这个测试实现并不完美。它只包括一种添加侦听器的方法。您可能希望包括一种删除不再对接收事件感兴趣的侦听器的方法。还要注意，这个类不是线程安全的

import java.util.List;
import java.util.ArrayList;
import java.util.EventListener;
import java.util.EventObject;
import java.awt.EventQueue; 

/**
 * This class uses the EventQueue to process its events, but you should only 
 * really do this if the changes you make have an impact on part of a GUI 
 * eg. adding a button to a JFrame.
 *
 * Otherwise, you should create your own event dispatch thread that can handle
 * change events
 */
public class BooleanChangeTest implements BooleanChangeDispatcher {

    public static void main(String[] args) {

        BooleanChangeListener listener = new BooleanChangeListener() {
            @Override
            public void stateChanged(BooleanChangeEvent event) {
                System.out.println("Detected change to: "
                    + event.getDispatcher().getFlag()
                    + " -- event: " + event);
            }
        };

        BooleanChangeTest test = new BooleanChangeTest(false);
        test.addBooleanChangeListener(listener);

        test.setFlag(false); // no change, no event dispatch
        test.setFlag(true); // changed to true -- event dispatched

    }

    private boolean flag;
    private List<BooleanChangeListener> listeners;

    public BooleanChangeTest(boolean initialFlagState) {
        flag = initialFlagState;
        listeners = new ArrayList<BooleanChangeListener>();
    }

    @Override   
    public void addBooleanChangeListener(BooleanChangeListener listener) {
        listeners.add(listener);
    }

    @Override
    public void setFlag(boolean flag) {
        if (this.flag != flag) {
            this.flag = flag;
            dispatchEvent();
        }
    }

    @Override
    public boolean getFlag() {
        return flag;
    }

    private void dispatchEvent() {
        final BooleanChangeEvent event = new BooleanChangeEvent(this);
        for (BooleanChangeListener l : listeners) {
            dispatchRunnableOnEventQueue(l, event);
        }
    }

    private void dispatchRunnableOnEventQueue(
                final BooleanChangeListener listener, 
                final BooleanChangeEvent event) {

        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                listener.stateChanged(event);
            }
        });
    }

}

interface BooleanChangeDispatcher {

    public void addBooleanChangeListener(BooleanChangeListener listener);
    public boolean getFlag();
    public void setFlag(boolean flag);

}

/**
 * Listener interface for classes interested in knowing about a boolean
 * flag change.
 */
interface BooleanChangeListener extends EventListener {

    public void stateChanged(BooleanChangeEvent event);

}

/** 
 * This class lets the listener know when the change occured and what 
 * object was changed.
 */
class BooleanChangeEvent extends EventObject {

    private final BooleanChangeDispatcher dispatcher;

    public BooleanChangeEvent(BooleanChangeDispatcher dispatcher) {
        super(dispatcher);
        this.dispatcher = dispatcher;
    }

    // type safe way to get source (as opposed to getSource of EventObject
    public BooleanChangeDispatcher getDispatcher() {
        return dispatcher;
    }
}