[Chapter 13] 13.2 IllegalComponentStateException

13.2 IllegalComponentStateException

IllegalComponentStateException is a subclass of IllegalStateException; both are new to Java 1.1. This exception is used when you try to do something with a Component that is not yet appropriate. With the standard AWT components, this can happen only in three instances:

If you call setCaretPosition() to set the cursor position of a text component before the component's peer exists.
If you call getLocale() to get the locale of a component that does not have one and is not in a container that has one.
If you call getLocationOnScreen() for a component that is not showing.

In these cases, the operation isn't fundamentally illegal; you are just trying to perform it before the component is ready. When you create your own components, you should consider using this exception for similar cases.

Since IllegalComponentStateException is a subclass of Run-TimeException, you do not have to enclose method calls that might throw this exception within try/catch blocks. However, catching this exception isn't a bad idea, since it should be fairly easy to correct the problem and retry the operation.

IllegalComponentStateException Method

Constructor

public IllegalComponentStateException ()

The first constructor creates an IllegalComponentStateException instance with no detail message.

public IllegalComponentStateException (String message)

This constructor creates an IllegalComponentStateException with a detail message of message. This message can be retrieved using getMessage(), which it inherits from Exception (and is required by the Throwable interface).

IllegalComponentStateException Example

The following code throws an IllegalComponentStateException. The Exception occurs because the TextField peer does not exist when setCaretPosition() is called. setCaretPosition() throws an IllegalComponentStateException, and the next statement never executes.

import java.awt.TextField;
public class illegal {
    public static void main (String[] args) {
        new TextField().setCaretPosition (24);
        System.out.println ("Never gets here");
    }
}


AWTException		AWTError