Question

This one’s a tough one – I have a JFrame that generates JTextFields. When I go from generating 2 JTextFields to 12 JTextfields (for example), I see some error where there is an extra differently-sized JTextField at the end. It seems to be a repaint error.

Main.java code:

import java.awt.*; import javax.swing.*;  public class Main {     public static Display display = new Display();      public static void main(String[] args) {         display.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);         display.setVisible(true);     } } 

Display.java code:

import java.awt.*; import java.awt.event.*;  import javax.swing.*;  public class Display extends JFrame {     final int FRAME_WIDTH = 820;     final int FRAME_HEIGHT = 700;     final int X_OFFSET = 40;     final int Y_OFFSET = 40;      final int GRAPH_OFFSETX = 35;     final int GRAPH_OFFSETY = 60;     final int GRAPH_WIDTH = 500;     final int GRAPH_HEIGHT = 500;     final int GRAPH_INTERVAL = 20;      JButton submit;     JTextField top;     JTextField bottom;     JTextField numPoint;     JPanel bpanel;     JPanel points;      int maxPoints;      public Display() {         init();     }      public void init() {         setBackground(Color.WHITE);         setLocation(X_OFFSET, Y_OFFSET);         setSize(FRAME_WIDTH, FRAME_HEIGHT);         setTitle('Geometric Transformations');         getContentPane().setLayout(null);         setDefaultLookAndFeelDecorated(true);          top = new JTextField();    // parameter is size of input characters         top.setText('1 2 3');         top.setBounds(590, 150, 120, 25);          bottom = new JTextField();    // parameter is size of input characters         bottom.setText('5 6 7');         bottom.setBounds(590, 200, 120, 25);          numPoint = new JTextField();         numPoint.setText('Number of Points?');         numPoint.setBounds(550,200,200,25);         this.add(numPoint);          SubmitButton submit = new SubmitButton('Submit');         submit.setBounds(570, 250, 170, 25);          bpanel = new JPanel(new GridLayout(2,3));         bpanel.add(top);         bpanel.add(bottom);         bpanel.add(submit);          points = new JPanel(new GridLayout(2,2));         points.setBounds(540,250,265,60);         this.add(points);          bpanel.setBounds(550,100,200,70);         this.add(bpanel, BorderLayout.LINE_START);          Component[] a = points.getComponents();         System.out.println(a.length);         repaint();     }      public void paint(Graphics g) {         super.paint(g);         g.setColor(Color.WHITE);         g.fillRect(100, 100, 20, 30);         g.setColor(Color.BLACK);         genGraph(g, GRAPH_OFFSETX, GRAPH_OFFSETY, GRAPH_WIDTH, GRAPH_HEIGHT, GRAPH_INTERVAL);     }      public void genGraph (Graphics g, int x, int y, int width, int height, int interval) {         // draw background         int border = 5;         g.setColor(Color.BLACK);         width = width - (width % interval);         height = height - (height % interval);         for (int col=x; col <= x+width; col+=interval) {             g.drawLine(col, y, col, y+height);         }         for (int row=y; row <= y+height; row+=interval) {             g.drawLine(x, row, x+width, row);         }     }     class SubmitButton extends JButton implements ActionListener {          public SubmitButton(String title){             super(title);             addActionListener(this);             this.setVisible(true);         }         public void actionPerformed(ActionEvent e) {             maxPoints = Integer.parseInt(numPoint.getText()) * 2;              points.removeAll();              for (int i=0; i<maxPoints; i++) {                 JTextField textField = new JTextField();                 points.add(textField);             }             points.validate();        // necessary when adding components to a JPanel             // http://stackoverflow.com/questions/369823/java-gui-repaint-problem-solved             // What to Check:             // Things between commas are either spaces (which will be stripped later)             // or numbers!              // Pairs must match up!         }     } } 

Answer 1

The new components are redrawn over the previous ones. I added points.repaint(); after points.validate(); and the problem was gone.