Question

I am attempting to make a form that takes user inputs for first name and last name and prints a welcome message combining the two. I wanted to group the input stuff together into a grid panel, then group the “Go” button and the text field that displays the message in another panel, and nest both of those together using a BorderLayout within one frame.

Generic layout:

(in a 3×2 grid)

First Name: __________________________  
Last Name:  __________________________  
Age:        _______________

“GO BUTTON” “Welcome Mark Summers”

The professor wants it all in one .java file which is my problem. I would normally separate these things then extend the classes and have no problem. What I’m trying to do is save the input and output panels under my constructor, then under my main, create

JFrame frame = new JFrame();

and then

add(new CalebBreckonHW3(320,120));

thereby putting a 320×120 panel inside my 700×700 JFrame “frame”. I get an error message though that I can’t reference the non-static method add(java.awt.Component) from a static context. I can’t set my main to non-static or I’ll get an error.

I’m in the process of adding the code to this right now through an Can anyone point me in the right direction?

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

public class CalebBreckonHW3 extends JFrame {
    private JButton jbtGreet = new JButton("Greet Me");
    private JLabel firstOprLbl = new JLabel("First name");
    private JLabel lastOprLbl = new JLabel("Last name");
    private JLabel ageOprLbl = new JLabel("Age");
    private JTextField jtfFirst = new JTextField(10);
    private JTextField jtfLast = new JTextField(15);
    private JTextField jtfAge = new JTextField(3);
    // I'll get to the action events after I get this down
    private JTextField jtfGreet = new JTextField("Welcome firstname, lastname");

    public CalebBreckonHW3(int height, int width) {
        setLayout(new BorderLayout());
        setSize(height, width);
        JPanel inputPanel = new JPanel();
        inputPanel.setLayout(new GridLayout(3,2,0,5));
        jtfGreet.setEditable(false);
        inputPanel.add(firstOprLbl);
        inputPanel.add(jtfFirst);
        inputPanel.add(lastOprLbl);
        inputPanel.add(jtfLast);
        inputPanel.add(ageOprLbl);
        inputPanel.add(jtfAge);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setTitle("Greeting App");
        frame.setSize(700,700);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);

        add(new CalebBreckonHW3(320,120));
    }
}

EDIT: Adding frame in front of my add statement gets rid of the static error but it gives me an error “adding a window to a container”

Answer 1

The problem is you extend the JFrame class from your class, but you initiate your own JFrame in main(), also you cannot call add() because you are in main which is static while add() requires an instance to be created before being called, see my comment on your question, however, you should not extend a JFrame and rather do:

public class CalebBreckonHW3  {

    public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {

        @Override
        public void run() {
        JFrame frame = new JFrame();
        frame.setTitle("Greeting App");
       // frame.setSize(700,700); //not recommened
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

         JPanel panel=new JPanel(/*set layout if needed*/); 
         //panel.add(new JButton("Hello")); //add components to panel

        frame.getContentPane().add(panel);//why did you add your JFrame again???? so I guess you'd wanna add a JPanel or something with the components you need.

        frame.pack();
        frame.setVisible(true);
       }

    });
 }
...
}

also always create a EDT (Event Dispatch Thread on which all UI components lay) I did this by SwingUtilities.invokeLater(); also always add to a JFrames contentPane via getContentPane().add();. Another thing, why do you add your Jframe to your Jframe? as you can see I showed an example of adding a JPanel

EDIT:

you make your JFrame a global variable and then you can use frame.setLayout() etc.

however if you want your current code to work do this:

public class CalebBreckonHW3  extends JFrame{

    public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {

        @Override
        public void run() {
        new CalebBreckonHW3().createandShowUI();
       }

    });
 }
 private void createAndShowUI() {
        setTitle("Greeting App");
        //setSize(700,700); //not recommened
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

         JPanel panel=new JPanel(/*set layout if needed*/); 
         //panel.add(new JButton("Hello")); //add components to panel

        getContentPane().add(panel);//why did you add your JFrame again???? so I guess you'd wanna add a JPanel or something with the components you need.

        pack();//this will override setsize and use LayoutManager
        setVisible(true);     
 }
...
}

but extending a JFrame is not recommended