Can I use switch - case, in actionPerformed method

问题:

I would like to check on which actionEvent has occurred with ActionEvent e and e.getSource(). Can I use a switch case for this?

public void actionPerformed(ActionEvent e){
    switch(e.getSource()){
        case radius:
            double r = validate(radius.getText());
            break;
        case height:
            double h = validate(height.getText());
            break;
        case out:
            out.setText(String.valueOf(h*r));
            break;
    }
}

回答1:

No, you can't. The types you can use in a switch statement is very limited. See The switch Statement.

You can of course just write this as a series of "if" and "else if" statements.

回答2:

Yes, you can use switch in actionPerformed.

No, you can't use it like you showed it here.

switch only supports primitive types and enums (and String, but only in Java 7 and later).

Another problem is that the case-values values must be compile time constants.

You'll need code like this:

public void actionPerformed(ActionEvent e){
    if (e.getSource() == radius) {
        double r = validate(radius.getText());
    else if (e.getSource() == height) {
        double h = validate(height.getText());
    else if (e.getSource() == out) {
        out.setText(String.valueOf(h*r));
    }
}

回答3:

As other solutions have pointed out, you cannot use switch in this context. However, rather than implementing one ActionListener containing a big if-then block, why not implement separate ActionListeners for each event source? This is a much more OO-based approach.

Typically your ActionListener implementations would be (small) anonymous inner classes anyway, and hence you wouldn't have to deal with a huge proliferation of .java files.

回答4:

The ActionEvent contains an ActionCommand field which is a String. If not set while creating the Button it defaults to the text of the button. You can use that instead.

Something like:

switch(e.getActionCommand()) {
    case: "Radius":
          ....
    case: "Height":
          ....
}