Class with JFrame

Question

I'm beginner of java and I study about JFrame now but I have an issue. I made a constructor with parameters of JPanel but when I invoke it with arguments, an error is happened. Could you help me to find any solutions??

import javax.swing.*;
import java.awt.Color;
import java.awt.Font;
import java.awt.*;

public class JFlexiblePanel extends JFrame{

    private Color col1;
    private Color col2;
    private Font font1;
    private String str;
    private JPanel panel1;
    private JLabel label1;

    public JFlexiblePanel(Color col1, Color col2, Font font1, String str) {
        this.col1 = col1;
        this.col2 = col2;
        this.font1 = font1;
        this.str = str;
        panel1.setBackground(this.col1);
        panel1.setForeground(this.col2);
        label1.setFont(this.font1);
        label1.setText(this.str);
        panel1.add(label1);
    }    
}

In different class to invoke this constructor

JFlexiblePanel p1 = new JFlexiblePanel(Color.BLUE, Color.RED, new Font("Arial",Font.BOLD,12), "America");

"an error is happened", can you be more specific about that part? — Stultuske, Apr 19 '18 at 13:47
You get NullPointerExceptions because you don't initialize your members before using them — Stultuske, Apr 19 '18 at 13:49
Thank you guys. NullPointerException was one of my error, and I learned about it because of you. Thank you. — YUKI, Apr 19 '18 at 14:24

score 0 · Answer 1 · answered Apr 19 '18 at 14:08

0

Your class name implies that it's a JPanel class. So it can't extends a JFrame, but have to extend JPanel. I think you are misunderstanding how they both work.

To be short : JFrame is the top Level of a "window" and is composed by JPanel.

Moreover, your Jpanel1 and JLabel1 are never instanciated, then the error might be here :

panel1.setBackground(this.col1);
panel1.setForeground(this.col2);
panel1.add(label1);

But if you want more help you have to give more information like the type of the error. Also consider this tutorial : link to tutorial

answered Apr 19 '18 at 14:08

Arnauld Alex

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Thank you for answering and yes, extending JPanel solved my problem. Thank you. – YUKI Apr 19 '18 at 14:25
No problem, please consider marking your question answered by my solution, have a good day – Arnauld Alex Apr 19 '18 at 14:26

Class with JFrame

1 Answers1