如何在用户更改之前将 JFormatedTextField 的值设置为无效字符串？

Question

because of a project I want to how to set the value of a JFormatedTextField, in a Java Swing GUI, to an invalid String, before the user changes the value oby himself.

Considering the fact that all the iddentifer names in the original code, which contains additional code, which is not usefull for this question, I decided to write a new short code, which contains the important part, for my question.

This is a shortened version of my code:

import javax.swing.*;
import javax.swing.text.*;
import java.text.*;
import java.awt.*;
public class myGUI{
    private JFrame f;
    private JPanel p;
    private JFormattedTextField ftf;
    private NumberFormat nf;
    private NumberFormatter nfter;
    public myGUI(){
        f = new JFrame("My Window");
        f.setSize(960,450);
        f.setDefaultCloseOperation(f.EXIT_ON_CLOSE);
        f.setLocationRelativeTo(null);
        f.setVisible(true);
        p = new JPanel();
        f.add(p);
        p.setLayout(new FlowLayout());
        nf = NumberFormat.getInstance();
        nfter = new NumberFormatter(nf);
        nfter.setAllowsInvalid(false);
        ftf = new JFormattedTextField(nfter);
        p.add(ftf);
        ftf.setValue("I want this as my ftfs value before it gets changed");
    }
}

When I execute this code, I get this error message:

java.lang.IllegalArgumentException: Cannot format given Object as a Number (in java.text.DecimalFormat)

I tried to solve this problem by myself by changing "nfter.setAllowsInvalid(false);" to "nfter.setAllowsInvalid(true);" but I received the same result.

Since I am not really familiar to Swing and only familiar to the most basic things about Java, I hope you can help me, with your experance and knowledge.

thanks for helping and sorry for my bad english skills!

Answer 1

Please use setText instead of setValue . You should put a number inside setValue method like setValue(99) .

ftf.setText("I want this as my ftfs value before it gets changed");

And don't forget nfr.setCommitsOnValidEdit(true) if you want your default text to be formatted as a number at beginning. Otherwise you will get null value before you typing something.