Question

I have a Class(call it main class) and the method in main class calls methods of other classes.I have extended this main class in all other classes like this

      public class Evaluate extends Main

in my main class i am using swingworker ,so i have written the code like this

      class Main extends SwingWorker<Void, Void>{
        public Main(GUI frame) {
        p = frame;

        }
        //some more code 

Now when i build this program, it gives me the following error

        error: constructor Main in class Main cannot be applied to given types;
        public class Evaluate extends Main {
        required: GUI
        found: no arguments
        reason: actual and formal argument lists differ in length

Here GUI contains the main method from where my application starts.Kindly help me why this error is occurring.

Answer 1

When you extend a class, you should call a constructor of the main class in your own constructor (by using super). So in this case, your Evaluate class should look like

public class Evaluate extends Main {

  public Evaluate( GUI frame ){
    super( frame );
  }
  // or another constructor
  public Evaluate( ){
    super( retrieveAFrameFromSomeWhere );
  }
  public Evaluate( loads of other arguments, GUI frame ){
    super( frame );
    //do something with the other arguments
  }
}

Check out the excellent Java tutorial for more information, and certainly the section about Subclass constructors