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Thread: Construct a class that implement ActionListener with no constructor

  1. #1
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    Default Construct a class that implement ActionListener with no constructor

    Hi, I am reading a passage in Java book that goes like this:

    class TimePrinter implements ActionListener {
    	public void actionPerformed(ActionEvent event) {
    		Date now = new Date();
    		System.out.println("At the tone, the time is " + now);

    Now to use TimePrinter we would do:

    ActionListener listener = new TimePrinter();
    Timer timer  = new Timer(20000, listener);

    I am confuse about creating a
    new TimePrinter();
    when the TimePrinter class have no constructor. From what I read, if a class have no constructor, it will then call the superclass of TimePrinter, which is Object, and use the default no-arg constructor. But I think its a bit confusing for me to create a class without constructor but only a method. Can somebody lighten me up on this a little bit more?
    Last edited by striko_514; July 26th, 2010 at 08:17 PM.

  2. #2
    Super Moderator helloworld922's Avatar
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    Default Re: Construct a class that implement ActionListener with no constructor

    In Java, if you have no explicitly defined constructor, there's a default constructor which initializes all values to their "default" value, i.e. nulls, 0's, etc. This is what's known as a an implicit constructor. Note that once you provide even 1 constructor for the class, you no longer get the implicit constructor.

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