Java Event Listener to detect a variable change

Question

I cannot seem to find an answer anywhere to my question. Is there any event listener which can detect the changing of a boolean or other variable and then act on it. Or is it p

Answer 1

you can also try to implement an Observer.

First create the observable object:

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);
 }

}

Then the observer:

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!");
  }
 }
}

And in your main (or wherever else):

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");
 }
}

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