CODEWITHSUNDEEP
javaswingactionlistener
botenvouwer
botenvouwer

Reputation: 4432

Use method as event listener instead of class

I always make an event listener for buttons and such like this:

class MyClass implements extends JPanel implements ActionListener{

      JButton btn1, btn2, btn3;      

      public Myclass(){
            ....
            btn1 = new JButton("button 1");
            btn1.addActionListener(this);
            ....
      }

      public void actionPerformed(ActionEvent e) {

            Object action = e.getSource();
            if(action = btn1){
                functionForBTN1();
            }
            else if(action = btn2){
                functionForBTN2();
            }
            else if(action = btn3){
                functionForBTN3();
            }

      }

      public void functionForBTN1(){...}
      public void functionForBTN2(){...}
      public void functionForBTN3(){...}

}

Is it possible to direct the event directly to a method instead of the actionPerformed() method? something like (pseudo-code):

class MyClass implements extends JPanel implements ActionListener{

          JButton btn1, btn2, btn3;      

          public Myclass(){
                ....
                btn1 = new JButton("button 1");
                btn1.addActionListener(this.functionForBTN1());
                ....
          }

          public void functionForBTN1(){...}
          public void functionForBTN2(){...}
          public void functionForBTN3(){...}
}

Upvotes: 1

Views: 79

Answers (3)

user2336315
user2336315

Reputation: 16067

As Maroun Maroun said an anonymous class is a good idea. With java-8 you could also use a lamdba which makes the code slightly nicer;

btn1.addActionListener(event -> functionForBTN1());

Upvotes: 1

ankh-morpork
ankh-morpork

Reputation: 1832

If you're using Java 8, you can accomplish this using a lambda expression.

btn1.addActionListener(e -> this.functionForBTN1());

Prior to Java 8, you could create an anonymous ActionListener to acomplish the same task.

btn1.addActionListener(new ActionListener(){
    @Override
    public void actionPerformed(ActionEvent e){
        this.functionForBTN1();
    }
});

Upvotes: 3

Maroun
Maroun

Reputation: 96018

You can use anonymous classes:

btn1.addActionListener(new ActionListener (){
     public void actionPerformed(ActionEvent e) {      
         // ....
     }
});

However, if you want to add it like you did in your second snippet, you can do something like:

final ActionListener listener = new ActionListener() {
    @Override
    public void actionPerformed(final ActionEvent e) {
        if (e.getSource() == btn1) {
            //...
        } else if (e.getSource() == btn2) {
            //...        
        }
    }
};

And then:

btn1.addActionListener(listener);
btn2.addActionListener(listener);

I personally prefer anonymous classes as long as they're readable and not too long.

Upvotes: 1

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