Please help me to understand how this works. I'm having difficulties to understand how, for example, JButton in one class can alter text in JTextArea that is in another class of a same package. I've made a simple app just to ask a question here, I need this for a bigger school project where I need to implement this to work with multiple classes.
When I put everything in the same class it works but I need it in separate classes.
Here is the simple code.
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
class Button extends JPanel {
private JButton button;
private Panel panel;
public Button() {
button = new JButton("BUTTON");
panel = new Panel();
add(button);
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
JButton clicked = (JButton) e.getSource();
String input = clicked.getText();
panel.setTextArea(input);
//System.out.println(input);
}
});
}
}
class Panel extends JPanel {
private JTextArea textArea;
public Panel() {
setLayout(new BorderLayout());
textArea = new JTextArea();
add(textArea, BorderLayout.CENTER);
}
public JTextArea getTextArea() {
return textArea;
}
void setTextArea(String text) {
this.textArea.setText(text);
}
}
public class Java extends JFrame {
private Button dugme;
private JFrame frame;
private Panel panel;
public Java() {
frame = new JFrame();
dugme = new Button();
panel = new Panel();
//super("test");
frame.setLayout(new BorderLayout());
frame.setTitle("test");
frame.setSize(300, 400);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
frame.add(dugme, BorderLayout.NORTH);
frame.add(panel, BorderLayout.CENTER);
}
public static void main(String[] args) {
Java app = new Java();
}
}
I want action listener to alter the text in the panel, sys-out works so the listener listens the button but I can't make it to alter the text in text area.
As already mentioned by #XtremeBaumer you have two different instances of Panel class. You need to remove the secode one.
public class Button extends JPanel {
private JButton button;
private Panel panel;
public Button(Panel panel) { // we need already created instance of panel here.
this.panel = panel;
button = new JButton("BUTTON");
// panel = new Panel(); <-- this line must be deleted.
// ...
}
}
public class Java extends JFrame {
private Button dugme;
private JFrame frame;
private Panel panel;
public Java(){
frame = new JFrame();
panel = new Panel();
dugme = new Button(panel);
// ...
}
}
Please also replace the line
add(textArea, BorderLayout.CENTER);
by
add(new JScrollPane(textArea), BorderLayout.CENTER);
This allows you to get the scrool bars when text goes larger than the text ara size.
Here is your reworked example
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
class Button extends JPanel {
private JButton button;
private Panel panel;
public Button(Panel panel) {
this.panel = panel;
button = new JButton("BUTTON");
add(button);
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
JButton clicked = (JButton) e.getSource();
String input = clicked.getText();
panel.setTextArea(input);
//System.out.println(input);
}
});
}
}
class Panel extends JPanel {
private JTextArea textArea;
public Panel() {
setLayout(new BorderLayout());
textArea = new JTextArea();
add(new JScrollPane(textArea), BorderLayout.CENTER);
}
public JTextArea getTextArea() {
return textArea;
}
void setTextArea(String text) {
this.textArea.setText(text);
}
}
public class Java extends JFrame {
private Button dugme;
private JFrame frame;
private Panel panel;
public Java() {
frame = new JFrame();
panel = new Panel();
dugme = new Button(panel);
//super("test");
frame.setLayout(new BorderLayout());
frame.setTitle("test");
frame.setSize(300, 400);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
frame.add(dugme, BorderLayout.NORTH);
frame.add(panel, BorderLayout.CENTER);
}
public static void main(String[] args) {
Java app = new Java();
}
}
Related
I'm trying to create a simple 500x500 applet with a button, 2-label, and textfield. The applet opens up but it is just blank no components are displaying nor will the color change. Not sure what is happening or what I'm missing exactly.
import java.applet.*;
import java.awt.Color;
import javax.swing.*;
public class Greeting {
private JFrame frame;
private JPanel panel;
private JLabel label1;
private JTextField textbox1;
private JButton button1;
private JLabel label2;
public Greeting(){
gui();
}
public void gui(){
frame = new JFrame("Greeting");
frame.setVisible(true);
frame.setSize(500, 500);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setResizable(false);
panel = new JPanel();
panel.setBackground(Color.YELLOW);
label1 = new JLabel ("Please enter your name");
textbox1 = new JTextField(20);
button1 = new JButton ("Greet");
panel.add(label1);
panel.add(button1);
panel.add(textbox1);
frame.getContentPane().add(panel);
frame.add(panel);
}
public static void main(String[] args) {
new Greeting();
}
}
If you are planning on displaying frame with all the components, then move the frame.setVisible(true) line to the end of the method:
public void gui() {
...
frame.add(panel);
frame.setVisible(true);
}
This allows for all the components to be added to the JFrame before it is displayed on the screen.
Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Unknown Source)
at java.awt.Container.add(Unknown Source)
at Volume.<init>(Volume.java:25)
at VolumeDriver.main(VolumeDriver.java:6)
I get the above errors when trying to run my program. My program is not complete but I just want to check what my window looks like so I can make sure it looks correct.
This is my worker class for right now
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Volume extends JFrame
{
private static final long serialVersionUID = 1L;
private JPanel topPanel;
private JPanel bottomPanel;
private JPanel rightPanel;
private JPanel mainPanel;
private JLabel message;
private final int width = 500;
private final int height = 400;
public Volume()
{
setTitle("Sphere and Box Volumes");
setSize(width,height);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
getContentPane().setLayout(new BorderLayout());
getContentPane().add(topPanel, BorderLayout.NORTH);
BuildTopPanel();
getContentPane().add(bottomPanel, BorderLayout.SOUTH);
BuildBotPanel();
getContentPane().add(rightPanel, BorderLayout.EAST);
BuildRightPanel();
getContentPane().add(mainPanel, BorderLayout.WEST);
BuildMainPanel();
setVisible(true);
}
private void BuildTopPanel()
{
topPanel = new JPanel(new FlowLayout());
topPanel.setBackground(Color.WHITE);
JTextField reqVolume = new JTextField(8);
message = new JLabel("Enter the required amount of volume:");
topPanel.add(message);
topPanel.add(reqVolume);
}
private void BuildBotPanel()
{
bottomPanel = new JPanel(new FlowLayout());
bottomPanel.setBackground(Color.WHITE);
JButton intialQuant = new JButton("Set Initial Quantities");
intialQuant.setActionCommand("I");
intialQuant.addActionListener(new ButtonListener());
JButton calcVolume = new JButton("Calculate Volumes");
calcVolume.setActionCommand("V");
calcVolume.addActionListener(new ButtonListener());
JButton close = new JButton("Close");
close.setActionCommand("C");
close.addActionListener(new ButtonListener());
bottomPanel.add(intialQuant);
bottomPanel.add(calcVolume);
bottomPanel.add(close);
}
private void BuildRightPanel()
{
rightPanel = new JPanel(new FlowLayout());
rightPanel.setBackground(Color.WHITE);
}
private void BuildMainPanel()
{
mainPanel = new JPanel(new FlowLayout());
mainPanel.setBackground(Color.WHITE);
}
private class ButtonListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
}
}
}
This is my driver class
public class VolumeDriver
{
public static void main(String[] args)
{
Volume frame = new Volume();
frame.setVisible(true);
}
}
Any help would be appreciated.
getContentPane().add(topPanel, BorderLayout.NORTH); // Uh oh! topPanel is not initialized!
BuildTopPanel();
You try to add your topPanel before its initialization in the BuildTopPanel() method, so it will obviously lead to a NPE!
This is also the case for your other build methods. Be sure to actually initialize and build your GUI elements before using them or adding them to your window!
For instance:
// Initialize GUI elements first:
BuildTopPanel();
BuildBotPanel();
BuildRightPanel();
BuildMainPanel();
// Then add the GUI elements to the window:
getContentPane().add(topPanel, BorderLayout.NORTH);
getContentPane().add(bottomPanel, BorderLayout.SOUTH);
getContentPane().add(rightPanel, BorderLayout.EAST);
getContentPane().add(mainPanel, BorderLayout.WEST);
initialize the component before you add it to panel. see the documents as below:
http://docs.oracle.com/javase/7/docs/api/java/awt/Container.html#add%28java.awt.Component%29
That means you need call BuildMainPanel() before getContentPane().add(mainPanel, BorderLayout.WEST);
The same with the other components.
Whenever I press "clear" in my Java GUI, it never works, please help me finish this. If i replace "textPanel" with another button, it works, otherwise with "textpanel" it doesn't.
Here is a lightweight version of my code demonstrating the problem:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class MainFrame extends JFrame {
private TextPanel textPanel;
private FormPanel formpanel;
public MainFrame(){
super("My Frame");
createLayout();
createFrame();
}
public void createFrame(){
setSize(600, 600);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setVisible(true);
}
public void createLayout(){
BorderLayout myLayout = new BorderLayout();
setLayout(myLayout);
textPanel = new TextPanel();
formpanel = new FormPanel();
// adding components
add(textPanel, BorderLayout.CENTER);
add(formpanel, BorderLayout.WEST);
}
public static void main(String[] args){
new MainFrame();
}
public static class FormPanel extends JPanel {
private JButton clear;
private TextPanel textPanel;
public FormPanel(){
clear = new JButton("Clear Cart!");
textPanel=new TextPanel();
add(clear);
clear.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent aev){
System.out.println("Test");
textPanel.setText("");
}
});
createGrid();
}
/* this methods simply creates the layout */
void createGrid(){
//creating layout
setLayout(new GridBagLayout());
GridBagConstraints gc = new GridBagConstraints();
gc.gridy++;
gc.weightx = .1;
gc.weighty = .1;
gc.gridx = 2;
gc.gridy=5;
gc.anchor = GridBagConstraints.LINE_START;
gc.insets = new Insets(0,0,0,0);
add(clear, gc);
}
}
public static class TextPanel extends JPanel {
private JTextArea textArea;
TextPanel (){
textArea = new JTextArea();
setLayout(new BorderLayout());
JScrollPane p = new JScrollPane(textArea);
add(p, BorderLayout.CENTER);
}
public void appendSomeText(String t){
textArea.append(t);
}
public void setText(String s){
textArea.setText(s);
}
}
}
You have two instances of TextPanel, one in MainFrame and the other one in FormPanel. TextPanel that is defined in FormPanel is actually not added to the panel, so textPanel.setText(""); has no effect on it as it is not visible.
When the text appended with Add To Cart! button it actually goes through a method in MainFrame - formEventOccurred() that executes textPanel.appendSomeText(). This is the other instance of TextPanel that is part of MainFrame and that is actually visible.
Looks like you need to move the duplicated logic from the main frame to the panels. Usually you should not extend JFrame as you are not adding any new functionality.
I am making a program that includes a GUI. For some reason, the JButton objects that I have created are not showing up onto my JFrame when I run the program. Here is the code:
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class ReverseAStringMain extends JPanel {
private JButton enterButton, exitButton;
private JTextField textField;
private JPanel buttonPanel;
private JTextArea textArea;
public ReverseAStringMain(){
JButton enterButton = new JButton("Enter");
JButton exitButton = new JButton("Exit");
enterButton.setPreferredSize(new Dimension(60,60));
exitButton.setPreferredSize(new Dimension(60,60));
ButtonListener listener = new ButtonListener();
enterButton.addActionListener(listener);
exitButton.addActionListener(listener);
buttonPanel = new JPanel();
buttonPanel.setPreferredSize(new Dimension(200,50));
buttonPanel.setBackground(Color.black);
buttonPanel.add(enterButton);
buttonPanel.add(exitButton);
textField = new JTextField();
textField.setSize(200, 100);
textArea = new JTextArea();
textArea.add(textField);
add(buttonPanel);
add(textField);
}
//Creating a ButtonListener class that implements the ActionListener interface
private class ButtonListener implements ActionListener{
#Override
//Overriding the ActionPerformed method of ActionListener
public void actionPerformed(ActionEvent action) {
if(action.getSource()== enterButton)
enterButton();
if(action.getSource()== exitButton)
System.exit(0);
}
}
private void enterButton() {
// TODO Auto-generated method stub
}
public static void main (String[] args){
JFrame frame = new JFrame("Raj's Reverse a String Program");
frame.setBackground(Color.white);
frame.setVisible(true);
frame.setResizable(false);
frame.setLocationRelativeTo(null);
frame.setSize(new Dimension(600,600));
//frame.pack();
frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new ReverseAStringMain());
}
}
If there are any problems or improvements I can make in my code, please let me know!
You're adding the components to your JFrame after it's visible. You should either add them to the JFrame before it's visible, or revalidate the JFrame after you add the components.
When I load your code (after making it a lot shorter in height), this is what I see:
I suspect this is more along the lines of what you expect to see.
Here is how I did it. Look carefully at:
The numbers provided to the BorderLayout constructor for white space between the panels.
The EmptyBorder for white space around the controls.
The use of pack() to shrink the GUI to the natural size.
The use of size hints in the construction of the text field and text area.
The use of a second layout - commonly known as a combined, or nested, layout.
import java.awt.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
public class ReverseAStringMain extends JPanel {
private JButton enterButton, exitButton;
private JTextField textField;
private JPanel pageTopPanel;
private JTextArea textArea;
public ReverseAStringMain(){
super(new BorderLayout(10,10));
setBorder(new EmptyBorder(5,15,5,15));
JButton enterButton = new JButton("Enter");
JButton exitButton = new JButton("Exit");
pageTopPanel = new JPanel(new FlowLayout(FlowLayout.CENTER));
pageTopPanel.setBackground(Color.black);
pageTopPanel.add(enterButton);
pageTopPanel.add(exitButton);
textField = new JTextField(5);
pageTopPanel.add(textField);
textArea = new JTextArea(4,40);
add(pageTopPanel, BorderLayout.PAGE_START);
add(textArea); // defaults to CENTER
}
public static void main (String[] args){
Runnable r = new Runnable() {
public void run() {
JFrame frame = new JFrame("XXX's Laid out Program");
frame.setBackground(Color.white);
frame.setResizable(false);
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new ReverseAStringMain());
frame.pack();
frame.setVisible(true);
}
};
SwingUtilities.invokeLater(r);
}
}
General Tips
Java GUIs might have to work on a number of platforms, on different screen resolutions & using different PLAFs. As such they are not conducive to exact placement of components. To organize the components for a robust GUI, instead use layout managers, or combinations of them1, along with layout padding & borders for white space2.
Generally, you want to set the frame visible After adding components
JFrame frame = new JFrame("Raj's Reverse a String Program");
frame.setBackground(Color.white);
frame.setResizable(false);
frame.setLocationRelativeTo(null);
frame.setSize(new Dimension(600,600));
//frame.pack();
frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new ReverseAStringMain());
frame.setVisible(true); <<------
Also, it is better practice to use .pack() insteack of .setSize(), so you had it right in the commented out //.pack()
If you wanted to set a size to the panel, you would override the getPreferredSize() like this
public Dimension getPreferredSize() {
return new Dimension(300, 300); // or whatever size you want
}
When you .pack(), this preferred size will be respected by the frame.
Also, not, setting the size of the JTextField won't work. What you want to do is pass it an integer value for the number of character spaces, like this
textField = new JTextField(20);
See an edited version of your program, with all the above mentioned points. One thing I also did was get rid of all your .setPreferredSizes. You will see the difference
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class ReverseAStringMain extends JPanel {
private JButton enterButton, exitButton;
private JTextField textField;
private JPanel buttonPanel;
private JTextArea textArea;
public ReverseAStringMain() {
JButton enterButton = new JButton("Enter");
JButton exitButton = new JButton("Exit");
//enterButton.setPreferredSize(new Dimension(60, 60));
//exitButton.setPreferredSize(new Dimension(60, 60));
ButtonListener listener = new ButtonListener();
enterButton.addActionListener(listener);
exitButton.addActionListener(listener);
buttonPanel = new JPanel();
//buttonPanel.setPreferredSize(new Dimension(200, 50));
buttonPanel.setBackground(Color.black);
buttonPanel.add(enterButton);
buttonPanel.add(exitButton);
textField = new JTextField(20);
//textField.setSize(200, 100); /// <<-----------
textArea = new JTextArea();
textArea.add(textField);
add(buttonPanel);
add(textField);
}
public Dimension getPreferredSize() {
return new Dimension(600, 600);
}
// Creating a ButtonListener class that implements the ActionListener
// interface
private class ButtonListener implements ActionListener {
#Override
// Overriding the ActionPerformed method of ActionListener
public void actionPerformed(ActionEvent action) {
if (action.getSource() == enterButton)
enterButton();
if (action.getSource() == exitButton)
System.exit(0);
}
}
private void enterButton() {
// TODO Auto-generated method stub
}
public static void main(String[] args) {
JFrame frame = new JFrame("Raj's Reverse a String Program");
frame.setBackground(Color.white);
frame.getContentPane().add(new ReverseAStringMain());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
Have a look at the Swing tutorial trail for more information on creating GUIs with Swing.
Try to add the buttonPanel to a Container, like this. And extend JFrame instead
Container contentpane = getContentPane();
contentPane.add(buttonPanel);
I am creating a GUI using Netbeans and my question is "how to remove the jpanel"...the hierarchical order as it is present Jframe->Jscrollpane->Jpanel->Jbutton. By clicking on the Jbutton I want to remove all components of the jpanel including the Jbutton(on which I am clicking) and the panel itself. Please do help.Urgent.THanks in advance
-Sayantan
private void b4ActionPerformed(java.awt.event.ActionEvent evt) {
final JPanel jp;
JTextField tf,of1,of2,xf,yf;
int i=1;
int m=(int)sp3.getValue();
JButton jb;
jp=new JPanel();
//jp.setLayout(new GridBagLayout());
DesignGridLayout layout = new DesignGridLayout(jp);
jsp2.getViewport().add(jp);
while(i<=m){
tf=new JTextField(5);
of1=new JTextField(5);
of2=new JTextField(5);
layout.row().grid(new JLabel("Type:")).indent(9).add(tf).grid(new JLabel("Length:")).indent().add(of1).grid(new JLabel("Breadth:")).indent().add(of2).empty();
fields1.add(tf);
fields1.add(of1);
fields1.add(of2);
xf=new JTextField(5);
yf=new JTextField(5);
layout.row().grid(new JLabel("X-axis:")).indent(9).add(xf).grid(new JLabel("Y-axis:")).indent().add(yf).empty(2);
fields1.add(xf);
fields1.add(yf);
i++;
}
jb=new JButton("Submit");
jb.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e)
{
for(JTextField field: fields1){
String s=field.getText();
lbr.setText(lbr.getText()+s);
}
lb3.setVisible(false);
sp3.setVisible(false);
b4.setVisible(false);
//jp.setVisible(false);
//jp.removeAll();
// jp.revalidate();
//jp.repaint();
// jsp2.remove(jp);
//jsp2.revalidate();
//jsp2.repaint();
}
});
layout.emptyRow();
layout.row().right().add(jb);
jp.revalidate();
jp.repaint();
// jsp2.revalidate();
//jsp2.repaint();
}
Note: I am using DesignGridLayout package.
This works:
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class ScratchSpace {
public static void main(String[] args) {
final JPanel panel = new JPanel();
panel.setOpaque(true);
panel.setBackground(Color.YELLOW);
panel.add(new JButton(new AbstractAction("Kill me") {
#Override
public void actionPerformed(ActionEvent e) {
panel.removeAll();
panel.revalidate();
panel.repaint();
}
}));
final JFrame frame = new JFrame();
frame.setContentPane(panel);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
I want to remove all components of the jpanel including the Jbutton(on which I am clicking) and the panel itself.
Then you need code something like:
JButton button = (JButtton)event.getSource();
JPanel grandparent = button.getParent().getParent();
grandparent.removeAll();
grandparent.revalidate();
grandparent.repaint();
Although I question any code where I see a removeAll(). You might look into using a Card Layout.