Question

Full disclaimer: I’m a CS student, and this question is related to a recently assigned Java program for Object-Oriented Programming. Although we’ve done some console stuff, this is the first time we’ve worked with a GUI and Swing or Awt. We were given some code that created a window with some text and a button that rotated through different colors for the text. We were then asked to modify the program to create radio buttons for the colors instead—this was also intended to give us practice researching an API. I’ve already handed in my assignment and received permission from my instructor to post my code here.

What’s the best way to implement button actions in Java? After some fiddling around, I created the buttons like this:

class HelloComponent3 extends JComponent     implements MouseMotionListener, ActionListener {     int messageX = 75, messageY= 175;      String theMessage;     String redString = 'red', blueString = 'blue', greenString = 'green';     String magentaString = 'magenta', blackString = 'black', resetString = 'reset';      JButton resetButton;     JRadioButton redButton, blueButton, greenButton, magentaButton, blackButton;     ButtonGroup colorButtons;      public HelloComponent3(String message) {      theMessage = message;      //intialize the reset button     resetButton = new JButton('Reset');     resetButton.setActionCommand(resetString);     resetButton.addActionListener(this);      //intialize our radio buttons with actions and labels     redButton = new JRadioButton('Red');     redButton.setActionCommand(redString);     ... 

And added action listeners…

redButton.addActionListener(this); blueButton.addActionListener(this); ... 

A stub was already created for the actionPerformed method to give us an idea on how to use it, but since there was only a single button in the template, it wasn’t clear how to implement multiple buttons. I tried switching on a String, but quickly realized that, since a String isn’t a primitive type, I couldn’t use it for a switch statement. I could have improvised with an if-else chain, but this is what I came up with instead. It seems far from elegant, and there must be a better way. If there is, what is it? Is there a way to switch on a string? Or choose an action in a more scaleable fashion?

public void actionPerformed(ActionEvent e){      if (e.getActionCommand().equals(resetString)) {         messageX = 75; messageY = 175;         setForeground(Color.black);         blackButton.setSelected(true);         repaint();         return;     }      if ( e.getActionCommand().equals(redString) ) {         setForeground(Color.red);         repaint();         return;     }      if ( e.getActionCommand().equals(blueString) ) {         setForeground(Color.blue);         repaint();         return;     }      if ( e.getActionCommand().equals(greenString) ) {         setForeground(Color.green);         repaint();         return;     }      if ( e.getActionCommand().equals(magentaString) ) {         setForeground(Color.magenta);         repaint();         return;     }      if ( e.getActionCommand().equals(blackString) ) {         setForeground(Color.black);         repaint();         return;     } } 

Answer 1

Instead of writing this:

resetButton.addActionListener(this); 

You could also write this:

resetButton.addActionListener(new ActionListener() {     public void actionPerformed(ActionEvent evt) {         resetButtonActionPerformed(evt);     } }); 

And instead of writing one big actionPerformed() for all actions, you can (and then have to) write this:

public void resetButtonActionPerformed(ActionEvent evt) {     messageX = 75; messageY = 175;     setForeground(Color.black);     blackButton.setSelected(true);     repaint(); } 

I don’t know if this is the most elegant solution, but at least you no longer have that big if construct.