Develop Reference

Weird Issue with JComponent Visibility

I am working on a GUI project with Swing in Java and the program is generally working fine. However, under each screen, I have a back button that calls the method of the screen before it and goes through the ArrayList containing all of the elements on the current screen and calls setVisible(false) on them. Upon running the program, the back button works correctly if you click it once but if you go back on the screen, and click it again, it takes two clicks for it to correctly work and then four clicks and then eight clicks and so on. I have no idea what is going on or why it is behaving this way as nothing in my code seems to do it. Also, sometimes, the button correctly returns to the previous screen but then keeps the components on the current screen active as if setVisible(false) was never called. The following code represents the general structure of my project. Is there anything that it is doing that is generating this problem?
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
public class MAIN {
static JFrame frame;
static JPanel panel;
public static void main(String [] args) {
mainScreen();
}
public static void mainScreen() {
JButton newScreen = new JButton("Next Screen");
frame = new JFrame();
panel = new JPanel();
panel.setBounds(0,0,1920,1080);
panel.setBackground(Color.cyan);
newScreen.setBounds(50, 500, 100, 500);
newScreen.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
newScreen.setVisible(false);
JButton returnButton = new JButton("return");
returnButton.setBounds(50, 50, 100, 100);
panel.add(returnButton);
returnButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
returnButton.setVisible(false);
mainScreen();
}
});
}
});
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
panel.add(newScreen);
frame.add(panel);
frame.setSize(1920,1080);
frame.setLayout(null);
frame.setVisible(true);
}
}

Drawing Area not showing up (not aligning correctly?)

I am wondering why the drawing area I have created is not showing up in my second panel. I have checked their locations uses getX and getY (250, 0, which is I am assuming the correct area for it to be since that would be the top left of the second panel), but I cannot seem to figure out what is wrong. I'm assuming this is a problem with some fundamental learning aspect of this that I do not have right, but cannot seem to figure out what the issue is. If you could explain to me what is going wrong and the proper direction as to where I would go about fixing it, that would be appreciated. I do have the drawing area working when I have it standalone; the issue is that I cannot get it to appear when working with other GUI components.
Thank you ^^
Code:
package Drawing;
import java.awt.Color;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSlider;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
public class DrawingApp extends JFrame{
public static void main(String[] args) {
GridLayout grid = new GridLayout(1, 2);
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
final DrawingComponent drawingArea = new DrawingComponent();
drawingArea.setSize(600, 250);
JPanel leftPanel = new JPanel();
JPanel rightPanel = new JPanel();
JSlider greSlider = new JSlider();
JSlider bluSlider = new JSlider();
JSlider redSlider = new JSlider();
Point leftLocation = new Point(0, 0);
Point rightLocation = new Point(250, 0);
JLabel greLabel = new JLabel("Green");
JLabel bluLabel = new JLabel("Blue");
JLabel redLabel = new JLabel("Red");
rightPanel.setLocation(rightLocation);
drawingArea.setLocation(rightLocation);
// JButton button = new JButton("Hello");
leftPanel.setSize(250, 600);
//leftPanel.setLocation(leftLocation);
leftPanel.setBorder((BorderFactory.createLineBorder(Color.black)));
rightPanel.setSize(250, 600);
//rightPanel.setLocation(rightLocation);
rightPanel.setBorder((BorderFactory.createLineBorder(Color.green)));
leftPanel.add(greLabel);
leftPanel.add(greSlider);
leftPanel.add(bluLabel);
leftPanel.add(bluSlider);
leftPanel.add(redLabel);
leftPanel.add(redSlider);
rightPanel.add(drawingArea);
frame.add(leftPanel);
frame.add(rightPanel);
//rightPanel.add(button);
frame.setSize(500, 600);
frame.setLayout(grid);
leftPanel.setVisible(true);
rightPanel.setVisible(true);
frame.setVisible(true);
class SlideClickListener implements ChangeListener
{
ChangeListener slideListener = new ChangeListener(){
#Override
public void stateChanged(ChangeEvent e){
if(e.getSource() == greSlider){
}
}
};
public void stateChanged(ChangeEvent ce) {
throw new UnsupportedOperationException("Not supportedyet.");
}
}
class MouseClickListener implements MouseListener
{
public void mouseClicked(MouseEvent event)
{
int x = event.getX();
int y = event.getY();
System.out.println(x + " " + y);
drawingArea.drawPoints(x,y);
}
// Do­nothing methods
public void mouseReleased(MouseEvent event) {}
public void mousePressed(MouseEvent event) {}
public void mouseEntered(MouseEvent event) {}
public void mouseExited(MouseEvent event) {}
}
MouseListener listener = new MouseClickListener();
drawingArea.addMouseListener(listener);
}
}
I can include the DrawingComponent class if needed, but assuming that it isn't since I know for sure that the class is working.

I'm assuming this is a problem with some fundamental learning aspect of this that I do not have right,
You don't appear to understand how layout managers work:
leftPanel.setSize(250, 600);
//leftPanel.setLocation(leftLocation);
rightPanel.setSize(250, 600);
//rightPanel.setLocation(rightLocation);
None of those statements will do anything. It is the job of the layout manager to determine the size and location of components added to the panel. In your case you are trying to use a GridLayout. So the components added to the grid will be given a size AFTER the decorations of the frame are taken into consideration. So even though the frame may be (500, 600), the space available to the panel will be less (because you need to account for the title bar and borders of the frame).
Also, you should assign the layout manager to the panel BEFORE you add components to the panel.
leftPanel.setVisible(true);
rightPanel.setVisible(true);
Swing components (except top level containers like JFrame, JDialog) are visible by default so the above code does nothing.
I can include the DrawingComponent class if needed,
Until a problem is solved you don't know what is or isn't relative to the problem. My guess is the your DrawingComponent is the problem. Again, the default layout manager of a JPanel is the FlowLayout which respects the preferred size of any component added to it. I'm guessing your DrawingPanel doesn't implement the getPreferredSize() method to the preferred size is (0, 0) so there is nothing to paint.
Read the section from the Swing tutorial on Custom Painting for more information and working examples to get you started.
I would suggest you also look at the Layout Managers section of the tutorial for layout basics and working examples.

Java - My action event doesn't work

I'm learning Java and Swing, but my JButton doesn't work.
import javax.swing.JFrame;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
public class Programma {
public static void main(String[] args) {
// TODO Auto-generated method stub
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
}
catch (Exception e){
e.printStackTrace();
}
JFrame frame = new JFrame("DIG");
JPanel panel = new JPanel();
JButton button = new JButton("Click Me");
frame.setSize(400, 400);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
button.setBounds(100, 100, 130, 35);
panel.add(button);
frame.add(panel);
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
JLabel label = new JLabel("Hello World");
label.setVisible(true);
panel.add(label);
}
});
}
}
The frame and button are visible, nut when I click it, the label doesn't appear. How can I fix this?
Do I write this before the other component like JPanel, JButton, etc., or do I write this at the end of code:
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
What is the difference ?
By the way, button.setBounds(100, 100, 130, 35) doesn't work, either.

I see some issues in your code:
button.setBounds(100, 100, 130, 35); that line will be ignored and you shouldn't be manually be determining the position of the components. See Null layout is evil and Why is it frowned upon to use a null layout in swing? altough you're not using null layout, there is explained why you shouldn't be manually determining the positions of the components.
You're running everything in your program in the main method, that will be hard to maintain later.
You're calling frame.setVisible(true) before you've added all your elements to it, that will cause you random issues.
You're not running your program on the Event Dispatch Thread (EDT), you can solve this by starting your program with the following code, which places it in the EDT. It's recommended as Swing is not thread safe.
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
//Your constructor here
}
});
}
You're setting the size of the JFrame with setSize(...), instead call frame.pack() and override the getPreferredSize() method of the JPanel.
After all the above has been said, you need to call revalidate() and repaint() on your ActionListener so your program paints its new state.
This program follows all the above recommendations and produces the following outputs (before clicking and after clicking the button 3 times), I on purpose to not make the images so large, made the GUI shorter (200 x 200 instead of 400 x 400)
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class Programma {
private JFrame frame;
private JPanel panel;
private JButton button;
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new Programma().createAndShowGui();
}
});
}
public void createAndShowGui() {
frame = new JFrame("DIG");
panel = new JPanel() {
#Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
};
button = new JButton("Click Me");
panel.add(button);
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
JLabel label = new JLabel("Hello World");
panel.add(label);
panel.revalidate();
panel.repaint();
}
});
frame.add(panel);
frame.pack();
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}
Do i write this before the other componente like JPanel,JButton... or do i write this at the end of code ?
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
What is the difference ?
Altough I answered this on the recommendations, the difference is that if you call setVisible before adding all your elements to the frame, then you'll find yourself with some random issues where the components are not all visible until you pass your mouse over them (or where they should be). frame.pack() and setVisible should be the last ones to be called in your program, and frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); can be at the start or the end, it doesn't affects, but I prefer to have it at the end too.
button.setBounds(100, 100, 130, 35); doesn't work too.
Well, that's because of you're using a layout manager (and that's the right way to do your GUIs) instead of a null-layout (which you shouldn't be using anyway) (See point #1).
Edit
What is the difference between frame.setSize(); and frame.setpack() ?
If you read the docs for pack():
Causes this Window to be sized to fit the preferred size and layouts of its subcomponents. The resulting width and height of the window are automatically enlarged if either of dimensions is less than the minimum size as specified by the previous call to the setMinimumSize method.
So, it will calculate the minimum size for your JFrame where all the elements are visible and in their preferred size while setSize will only set the window size, but if you place a JScrollBar inside it for example this will reduce the window size, because of that, that's why you should override the getPreferredSize(...) method of your container, so it will calculate its preferred size including the width of the JScrollBar or some other elements that could modify its size. See Should I avoid the use of setPreferred|Maximum|MinimumSize in Swing? (the general consensus says yes)

When you add components dynamically to panel, you need to repain it.
Do this
panel.revalidate();
after
panel.add(label);

Put one JPanel onto another JPanel from a different Java class

I'm developing Java Swing application. My application has two Java classes. Inside class1.java, I include JFrame, JButton and JPanel (panel1). When I click the button I want to hide panel1 and should be shown panel2 of class2.java. I tried this method in button actionPerformed method of class1.java. But it was not working.
class2 pnl = new class2();
this.remove(panel1);
this.add(pnl);
this.validate();
this.repaint();

Analysis
You simply want the JComponents to be displayed on the JFrame. We can achieve this by using a single JPanel, but adding and removing the JComponents from it, during the JButton's action listener.
Without looking at your actual code, it is better to make a manageable way to reach code and instantiated Objects. The code listed below, creates a nice and manageable way to do so.
Achieving This
The entire class is listed below with comments for explanations.
package swing;
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class MultiPaneledFrame {
JFrame frame = new JFrame();
JPanel window = new JPanel();
// As you can see, we create an array containing all your JComponents.
// We have two of these, to simulate multiple JPanel's.
List<JComponent> window1Contents = new ArrayList<JComponent>();
List<JComponent> window2Contents = new ArrayList<JComponent>();
// NOTE: The above Lists can instead be stuck in their own class like asked for,
// and instantiated on Class invocation.
JButton goto2 = new JButton("Goto Panel 2");
JButton goto1 = new JButton("Goto Panel 1");
int panelToShow = 0; // 0 - First "panel".
// 1 - Second "panel".
// Main method of class. Change 'Multi_Paneled_Frame' to the name of your Class.
public MultiPaneledFrame() {
// Execute anything else you want here, before we start the frame.
window1Contents.add(goto2);
window2Contents.add(goto1);
// Here is where I personally am setting the coordinates of the JButton's on the JPanel.
goto2.setPreferredSize(new Dimension(200, 100));
goto1.setPreferredSize(new Dimension(200, 100));
//goto2.setBounds(5, 5, 150, 30); < Used for 'null' layout.
//goto1.setBounds(5, 5, 150, 30); < Used for 'null' layout.
goto2.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
addComponents(panelToShow = 1);
}
});
goto1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
addComponents(panelToShow = 0);
}
});
initialiseFrame();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new MultiPaneledFrame();
}
});
}
private void initialiseFrame() {
frame.setSize(600, 400); // Change it accordingly.
// Optional
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
frame.setResizable(false);
// Needed
frame.setVisible(true);
frame.add(window);
window.setLayout(new BorderLayout()); // Assuming your using a BorderLayout.
//window.setLayout(null); < Uses 'null' layout.
addComponents(panelToShow);
// I always like to make sure that everything is on the frame nicely.
frame.repaint();
frame.validate();
}
private void addComponents(int panelNo) {
if (panelNo == 0) {
for (JComponent component : window1Contents) {
window.removeAll(); // We're removing everything that it contains and replacing it...
window.revalidate();
window.add(component, BorderLayout.CENTER);
//window.add(component); < Uses 'null' layout.
// Since we are using the first panel, we are adding
// everything from the first list of components to the window...
}
} else {
for (JComponent component : window2Contents) {
window.removeAll(); // We're removing everything that it contains and replacing it...
window.revalidate();
window.add(component, BorderLayout.CENTER);
//window.add(component); < Uses 'null' layout.
// Since we are using the second panel, we are adding
// everything from the second list of components to the window...
}
}
// Refreshes the frame.
frame.repaint();
frame.validate();
}
}
Conclusion
Although there are countless ways to achieve something like this, the way I have given, is semi-efficient, and very flexible. Feel free to edit the code, or drop a question if you have any concerns, and I will be happy to respond.
PS: This code was tested and works on a Macbook Air running OS X 10.11 and Java Version 8 Update 65.

CardLayout should be your solution. In this tutorial they show how to switch from panel to another one by selecting a value in ComboBox.
A little bit of explanation for the CarLayout:
The CardLayout lets you place different panel on top of each other but shows only one at the time. With your code, you select the one you want to display.
Initialisation:
this.setLayout(new CardLayout());
class1 pnl1 = new class1();
class2 pnl2 = new class2();
this.add(pnl1, "PANEL1");
this.add(pnl2, "PANEL2");
On your button actionPerformed:
CardLayout cl = (CardLayout)(this.getLayout());
cl.show(this, "PANEL2");

CardLayout performance?

I thought that CardLayout uses a HashMap to store its pairs (panels and associated string identifiers) but looking through the CardLayout class I noticed that it actually uses a Vector. This is how I understand it: when the show method is called it loops through the contents of the vector checking with equals to find out if this is the name of the appropriate card, and if it is, it then loops through all the panels of the container to find out which one is currently visible, it hides it, and then it displays the appropriate card.
If I was making a gui app that has a lot of different panels wouldn't that be kind of slow technique to flip to the desired panel? Should I better use my own way of showing my panels like storing them to an array and manually using add/remove or setVisible instead of using CardLayout? This is actually the way I was using at the beginning before I ended up to CardLayout.

This will never be an issue: you don't normally flip between components very frequently, and when you do then scanning a list with a smallish number of compoenents (usually 3-100?) is going to take a negligible amount of time compared with other operations that will have to happen (e.g. drawing the new component). Choice of data structure is basically irrelevant from a performance perspective - you could use a linked list and nobody would notice.
Also note that a HashMap wouldn't be appropriate for a CardLayout as it needs to preserve the order of the cards so that you can use first/next/previous etc.
So basically, don't worry and don't waste your time rolling your own CardLayout clone - CardLayout works just fine.

I don't find any performance issue in CardLayout. Even if you have a 1000 child components, it still feels very fast. Either by using previous/next or using show, it goes really fast.
Try to post an SSCCE that reproduces your problem and then we may help you. Here is something to start from:
import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class TestCardLayout {
protected void initUI() {
JFrame frame = new JFrame("test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
final CardLayout layout = new CardLayout();
final JPanel panel = new JPanel(layout);
for (int i = 0; i < 1000; i++) {
panel.add(new JLabel("Label " + i), getLabelConstraint(i));
}
JButton next = new JButton("Next");
next.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
layout.next(panel);
}
});
JButton previous = new JButton("Previous");
previous.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
layout.previous(panel);
}
});
final JButton choose = new JButton("Choose");
choose.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
String value = JOptionPane.showInputDialog(choose, "Enter a number between 0 and 999");
try {
int i = Integer.valueOf(value);
if (i > -1 && i < 1000) {
layout.show(panel, getLabelConstraint(i));
}
} catch (NumberFormatException e1) {
e1.printStackTrace();
}
}
});
JPanel buttonPanel = new JPanel();
buttonPanel.add(previous);
buttonPanel.add(next);
buttonPanel.add(choose);
frame.add(buttonPanel, BorderLayout.SOUTH);
frame.add(panel);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
private String getLabelConstraint(int i) {
return "ComponentConstraint" + i;
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new TestCardLayout().initUI();
}
});
}
}