JOptionPane取消按钮并获取输入

Question

I'm trying to get the user to input there name if it is left blank it will ask again, if they fill it out it sets a JLabel or hit cancel to get out.
My last if statement is wrong it does not like nameEnt .

public Player() {
    //setBackground(Color.green);
    setSize(600, 400);
    name = new JLabel();//Input hint
    JOptionPane nameOption = new JOptionPane();
    String nameEnt = nameOption.showInputDialog("First Name: ");
    if (!nameEnt.matches("[a-zA-Z]+")) {
        name.setText(nameEnt);
    }
    if (nameEnt.length() == 0) {
        //if this condition is true JOption stays until name is entered or canceled 
    }
    if (nameEnt == nameOption.CANCEL_OPTION) {
        System.exit(0);
    }
}

Answer 1

The JOptionPane.CANCEL_OPTION is a static int field, and you can't compare String with int with == .

---

Good practice

In your case you want to use ok and cancel button JOptionPane.showConfirmDialog and JOptionPane.showInputDialog() in one shot and this is not possible, i suggest to use this instead :

JTextField nameF = new JTextField(20);//create TextField

JPanel myPanel = new JPanel();//cerate JPanel
myPanel.add(new JLabel("Name"));
myPanel.add(nameF);//add your JTextField to your panel

int result;
do {
    result = JOptionPane.showConfirmDialog(null, myPanel,
            "Title of Panel", JOptionPane.OK_CANCEL_OPTION);//add your panel to JOptionPane
    if (result == JOptionPane.OK_OPTION) {//if the user press OK then
        if (nameF.getText().isEmpty()) {//check if the input is empty
            //if this condition is true JOption stays until name is entered or canceled 
        } else if (!nameF.getText().matches("[a-zA-Z]+")) {//check if the input match with your regex
            //name match exactly
            //name.setText(nameF.getText());
        }
    }
} while (result != JOptionPane.CANCEL_OPTION);//If the user hit cancel then exit

Answer 2

As per the JOptionPane API , if the user cancels the dialog, null is returned.

And so the correct solution is to to not to use equals, but rather to check the return value for null and to do this first, before checking its length.

public Player() {
    //setBackground(Color.green);
    setSize(600, 400);
    name = new JLabel();//Input hint
    JOptionPane nameOption = new JOptionPane();
    String nameEnt = nameOption.showInputDialog("First Name: ");
    if (nameEnt == null) {
        // user canceled. get out of here. 
        System.exit(0);

        // or return;  
        // or throw some exception
    }
    if (!nameEnt.matches("[a-zA-Z]+")) {
        name.setText(nameEnt);
    }
    if (nameEnt.length() == 0) {
        //if this condition is true JOption stays until name is entered or canceled 
    }
    // if (nameEnt == nameOption.CANCEL_OPTION) {
       //  System.exit(0);
    // }
}

But why are you creating a JOptionPane this way? Better to use the static method of creation.

// don't use null as the first parameter if the GUI is already showing
String nameEnt = JOptionPane.showInputDialog(null, "First Name: ");
if (nameEnt == null) {
    // user canceled. get out of here. 
    System.exit(0);
}

Or maybe something like this, if you're trying to loop to get input:

public Player() {
    setSize(600, 400);  // This is not good to do. Ask for details and I'll tell.

    name = new JLabel();// Don't forget to add this to the GUI!

    String nameEnt = "";
    while (nameEnt.trim().isEmpty()) {
        // if the GUI is already showing, pass a component from it as the first param here, not null
        nameEnt = JOptionPane.showInputDialog(null, "First Name: ");
        if (nameEnt == null) {
            // user canceled. get out of here. 
            System.exit(0);

            // or return;  
            // or throw some exception
        } else if (!nameEnt.matches("[a-zA-Z]+")) {
            name.setText(nameEnt);
        } else {
            // set it to "" so that we keep looping
            nameEnt = "";
        }
    }
}