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Java dynamically create buttons and pass a parameter to action performed

I am new to java and i am trying a small project on my own, i want to list the first and lastname of users from a sql database (this all works fine, but i don't just want to list them
I want to list all users in a GUI with a delete button, naturally this delete button will be generated dynamically and i want to pass the userID of the button to the action performed.
like this:
John Doe 'Delete button'
Jane Doe 'Delete button'
In my code below i just generate 16 buttons dynamically (without a users table) instead of passing the userID i am trying to pass the 'i' value of the for loop, but my code does not seem to work
CODE
public class UsersView implements ActionListener {
JFrame frame = new JFrame();
JPanel panel = new JPanel();
public UsersView() {
//Create the 16 buttons.
for (int i=0; i<16; i++) {
Button button = new Button("Click "+i);
button.setId(i); //this gives me and error 'Symbol not find' on the 'setId'
panel.add(button);
button.addActionListener(this);
}
panel.setBorder(BorderFactory.createBevelBorder(0, Color.lightGray, Color.yellow));
//panel.setBorder(BorderFactory.createEmptyBorder(300, 300, 100, 300));
panel.setLayout(new GridLayout(4,4)); //Rows Cols
frame.add(panel, BorderLayout.CENTER);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setTitle("App GUI");
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
// TODO code application logic here
new UsersView();
}
//On button click.
#Override
public void actionPerformed(ActionEvent e) {
//I know i have nothing here (yet) that is because the 'setId' gives me an error.
}
}

One of the issues you're having is creating a monolithic action listener, and then expecting to delegate actions from that. One nice feature of java are anonymous classes, or since java 7 lambdas.
JButton button = new JButton("Click " + i);
panel.add(button);
int id = i;
button.addActionListener( evt->{
performActionOnId( id );
});
Now instead of having the main class be an action listener, the main class has methods that are descriptive.
public void addUser( User a ){
//just showing delete button.
JButton delete = new JButton("X");
delete.addActionListener( evt ->{
removeUser( a );
//clean up gui.
});
}
This puts some of the steps of delegation at the creation of the user. Otherwise you'll have to delegate in your action performed.
public void actionPerformed( ActionEvent evt ){
//has to be a new class to have id attribute.
CustomButton b = (CustomButton)evt.getSource();
int id = b.getId();
User u = getUserById(id);
removeUser(u);
}

Use a JButton instead of Button. Mixing AWT and Swing components rarely works well, if at all. If you want to set a custom field for a component, just subclass it (use direct subclassing or a decorator pattern with composition). E.g.:
public class IdButton extends JButton {
private int id;
public IdButton(String label, int id) {
super(label);
this id = id;
}
public int getId() {
return id;
}
}
The J/Button classes do not have set/getId methods on it's own.

JButton in separate class won't change JTextField(Area) text in different class

I have a JFrame which contains 3 JPanels (each in a separate class). The first JPanel contains two JTextFields in which I write the name of the file to be read from and the condition to be fulfilled respectively. This doesn't really affect my question, so let's move on.
The second JPanel has a JTextArea.
The third JPanel has two JButtons (Load, Sort) which are supposed to load a list of entries that suffice the condition from the first JPanel and then reorganize them according to some rules (respectively).
THE PROBLEM:
Ok so, the first class is the JFrame class in which i just do the standard look and feel of the window.
The second class is the first JPanel with two JTextFields.
I won't give code for this one because the second JPanel code is shorter and has the same problem so I imagine that the same solution would apply.
Third class contains the JTextArea in which I should display certain entries from the text-file.
Code:
public class SecondPanel extends JPanel {
JPanel panel;
JTextArea lista;
public SecondPanel() {
panel = new JPanel();
list = new JTextArea("List");
list.setPreferredSize(new Dimension(200, 150));
this.add(list);
}
}
Moving on, the fourth class contains the Jbuttons and the ActionListener(Button listener). Ok so here is the part of the code from the button listener class
CODE:
private class ButtonListener implements ActionListener {
SecondPanel secondPanel = new SecondPanel();
FirstPanel firstPanel = new FirstPanel();
#Override
public void actionPerformed(ActionEvent e) {
if(e.getActionCommand().equals("Load")) {
//calls method that loads data from the text in a firstPanel field
loadData(firstPanel.theFile.getText());
for(int i = 0; i< students.length; i++) {
if(students[i]!=null) {
// doesn't write anything tried with .setText etc.
secondPanel.list.append(students[i]+"\n");
}
}
}
}
}
So the program won't get text when i type in the JTextField designated for the file path. And when i do it manually in the code, It won't write the changes to the list on the Window (JTextArea). But when i System.out.print to the console it prints the changes and lists entries correctly as well as any setText changes I make. It just won't write or read to and from the Window..
What should I do?

The problem is that you are calling your setText methods on the wrong objects.
In your listener class, you declared two new panels as class variables, and then you call your methods on them, but i think those panels are not the ones you really want to change.
You should first add your panels to your Jframe object, and refer to them on your ActionListener.
Here i provide you a minimal code which modifies a JTextArea when a JButton is pressed. (same for a JTextField)
import java.awt.*;
import javax.swing.*;
public class MyJFrame extends JFrame {
SecondPanel sPanel;
public MyJFrame() {
super("main");
Container c = getContentPane();
c.setLayout(new BorderLayout());
JButton button = new JButton("load");
button.addActionListener(new LoadListener());
c.add(sPanel = new SecondPanel(), BorderLayout.NORTH);
c.add(button, BorderLayout.SOUTH);
pack();
setVisible(true);
}
class SecondPanel extends JPanel {
public JTextArea list;
public SecondPanel() {
super();
list = new JTextArea("List");
list.setPreferredSize(new Dimension(200, 150));
add(list);
}
}
class LoadListener implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
sPanel.list.setText("new text for the jtext area");
}
}
public static void main(String[] args) {
new MyJFrame();
}
}

Dynamically add jcheckbox in jpanel

I have to add dynamically jcheckboxes in a panel when the user write something into a form. That's my code
Main
public class EmptyFrame extends JFrame{
private static final long serialVersionUID = 1L;
/*top panels*/
//to add technicians
private JButton newTechnician;
private NewTechForm ntForm;
private JPanel panelForm;
private JPanel panelChekBoxes;
TechCheckBoxGroup techniciansGroup;
private List<String> technicians;
//main container
private Container pane = getContentPane();
//components
GroupLayout gl = new GroupLayout(pane);
EmptyFrame(){
preinit();
init();
}
private void preinit(){
panelChekBoxes=new JPanel();
panelForm=new JPanel();
techniciansGroup=new TechCheckBoxGroup(panelChekBoxes);
}
private void init(){
/*top options*/
ntForm=new NewTechForm(panelForm);
newTechnician=new JButton("Add technician");
newTechnician.addActionListener(
new AddTechnicianAction(techniciansGroup,ntForm)
);
ntForm.getPanel().add(newTechnician);
/*end top options*/
for(String technic : technicians){
techniciansGroup.addCheckBoxes(
new JCheckBox(technic));
}
createWindowLayout(
new JLabel("Technicians"),
techniciansGroup.getCheckBoxes(),
ntForm.getPanel());
}
public void createWindowLayout(JComponent... arg) {
pane = getContentPane();
gl = new GroupLayout(pane);
pane.setLayout(gl);
gl.setAutoCreateContainerGaps(true);
gl.setAutoCreateGaps(true);
gl.setHorizontalGroup(gl.createParallelGroup()
.addGroup(gl.createSequentialGroup()
.addComponent(arg[0])
.addComponent(arg[1])
.addComponent(arg[2])
)
);
gl.setVerticalGroup(gl.createSequentialGroup()
.addComponent(arg[0])
.addGroup(gl.createParallelGroup()
.addComponent(arg[0])
.addComponent(arg[1])
.addComponent(arg[2]))
);
pack();
}
public static void main(String[] args) {
EventQueue.invokeLater(() -> {
EmptyFrame ex = new EmptyFrame();
ex.setVisible(true);
});
}
}
in the main are presents a form and a checkbox group the first is the ntForm and the second one is the techniciansGroup. When i insert a name inside the form i would like to add a checkbox inside the checkbox group, here are the button, the checkbox group and the form classes:
AddTechnicianAction
this would be the class where everything would happened
public class AddTechnicianAction implements ActionListener{
TechCheckBoxGroup technicians;
NewTechForm form;
JTable table;
public AddTechnicianAction(TechCheckBoxGroup arg0, NewTechForm arg1){
technicians=arg0;
form=arg1;
}
#Override
public void actionPerformed(ActionEvent arg0) {
System.out.println("Add new tech: "+this.form.getSurnameText().getText()+" "+this.form.getNameText().getText());
technicians.addCheckBoxes(new JCheckBox(this.form.getSurnameText()+" "+this.form.getNameText()));
System.out.println(technicians);
}
}
NewTechForm
this is the form
public class NewTechForm {
private JLabel nameLabel;
private JLabel surnameLabel;
private JTextField nameText;
private JTextField surnameText;
private JPanel panel;
public NewTechForm(JPanel panel){
nameLabel= new JLabel("Nome: ", JLabel.RIGHT);
surnameLabel = new JLabel("Cognome: ", JLabel.CENTER);
nameText = new JTextField(6);
surnameText = new JTextField(6);
this.panel=panel;
panel.add(nameLabel);
panel.add(nameText);
panel.add(surnameLabel);
panel.add(surnameText);
}
public JLabel getNameLabel() {
return nameLabel;
}
public JTextField getNameText() {
return nameText;
}
public JTextField getSurnameText() {
return surnameText;
}
public JLabel getSurnameLabel() {
return surnameLabel;
}
public JPanel getPanel() {
return panel;
}
}
The problem is that inside TechCheckBoxGroup something happens, but not the things that i'm expecting to. The panel have a new checkbox after the action is performed but it seems that that panel (the obne inside TachCheckBoxGroup) is not the one inside the main class, and infact nothing were rendered in the window. There is clearly something that i didn't understand about the scoping in swing, what's the better practice to do what i'm trying to? Or this is the good way and i miss something?

I think that it is important to have answers on stack overflow, so for that reason I post my answer to my problem even if it's not really easy to see that was the right solution, now I explain better. While I'm trying to solve the problem of the wrong behaviour I've asked my self if I was doing the wrong considerations, and so it was, because i was trying to let comunicate all the components without a real
mediator
in fact it was impossible to catch the event in the main window with the code that i had written above. Seaching and searching i finally find this great answer here. So i basically change the NewTechForm classes making it a jpanel with a form inside, same thing for the CheckGroupBox, i'll made it a panel with the check box inside, and i send all the event to a listener in the main window.

How to change a JLabel with a button from another class?

I have two classes and a text file database, The JLabel in the first class, let's call it class1 automatically set it self to the number in the database. Now, in class2 I have this little JFrame and a text field and of course a button, the value I put in the text field overwrites the one in the database, but here's the problem. The label in the first class wont update while running, but if I restart it it will show me the value that I want.
How do I update it while the program is running?
I've tried to change the label in the buttonActionperformed in the other class but it gives me a NullPointException every time.
How do I fix this?
THE MAIN CLASS ( JUST THE JFRAME )
package BankrollG;
import java.awt.Graphics;
import javax.swing.JFrame;
public class BGbrain {
BGbody body = new BGbody();
JFrame Frame = new JFrame();
public BGbrain() {
Frame.setSize(body.width, body.height);
Frame.setTitle(body.title);
Frame.setResizable(false);
Frame.setDefaultCloseOperation(Frame.EXIT_ON_CLOSE);
Frame.add(body.panel);
Frame.setLocationRelativeTo(null);
Frame.setFocusable(true);
Frame.setVisible(true);
}
public static void main(String[] args ) {
new BGbrain();
}
}
Then you got the class with the components:
private JLabel bankroll_label
public BGbody(){
panel.setLayout(null);
windowComponents();
}
public void windowComponents() {
// Bankroll database access
try {
FileReader fr = new FileReader("Bankroll.txt");
BufferedReader br = new BufferedReader(fr);
set_bankroll = br.readLine();
} catch(IOException e) {
System.out.println("FEL MED LÄSNING AV DATABAS /// BGBODY");
}
}
}
THEN you got the JFrame class that I created with the netbeans function
private void AddcurrencyActionPerformed(java.awt.event.ActionEvent evt) {
String CBR = txt_bankroll.getText();
try {
FileWriter fw = new FileWriter("Bankroll.txt");
PrintWriter pw = new PrintWriter(fw);
pw.println(CBR);
pw.close();
} catch(IOException e) {
System.out.println("FEL MED INSKRIVNINGEN I DATABASEN");
}
}
Now, everything goes as plan, but I can't update my JLabel "bankroll_label" from the button class because it just returns nullpointsexceptions. The data is there, because the JLabel reads from the database but it wont update when changes has been made from the button class. So a getter setter method wont work because the value IS there but it wont update the JLabel.
I hope this made it easier to understand my problem.
It's ALOT more code, that dont have to do with this, I hope I simplified it at least some.

Your question is a specific example of a basic problem in programming in Java -- how to transfer information between classes. There are several ways to do this, one of the most elegant being giving to use a "model" class that holds your program's logic code and key data, having one class change the model's state by changing a text String that it holds. Then using a listener or observer pattern, have the model notify the other class that it has been changed so the other class can extract the new information, its new String from the model. While this is likely the best solution, it may be a bit of overkill and likely is above your current level of coding, so for you, I'm not going to recommend this.
Instead, I'm going to recommend a simpler less elegant solution, that you instead have one class call a setter method of the other to push the new String into it.
One problem we have as volunteer answerers here is that your question is hard to answer because it lacks critical code, making it hard for us to guess why your code is misbehaving, why specifically you're running into a NullPointerException (or NPE) when you try to run it. So all I can do is guess, but guess I will try nevertheless.
For simplicity's sake, let's call one class the, the one that holds the JLabel, the LabelClass and the other class the ButtonTextFieldClass.
One possible reason is that you've got a NullPointerException is because your ButtonTextFieldClass may have a LabelClass variable, but never initialized the variable, something like so:
// this guy is null because it is never initialized
private LabelClass labelClass;
A simple solution could be to try to initialize it like so:
private LabelClass labelClass = new LabelClass();
But this won't work because while it does create and assign a LabelClass instance, it's likely not the LabelClass instance that is visualized in the running GUI.
A better solution is to give the ButtonTextFieldClass a setter method that allows other classes to set the ButtonTextFieldClass with the proper LabelClass instance.
e.g.,
public void setLabelClass(LabelClass labelClass) {
this.labelClass = labelClass;
}
This way the code that sets up both classes can pass the visualized LabelClass to the first class, and it can call methods on it.
A simple example of LabelClass could look like so:
class LabelClass extends JPanel {
private JLabel label = new JLabel("");
public LabelClass() {
setBorder(BorderFactory.createTitledBorder("Label Panel"));
add(label);
}
public void setLabelText(String text) {
label.setText(text);
}
}
I have it extend JPanel because this way it gives me the freedom of placing it into a JFrame or JDialog or other JPanel as I see fit. Note that I've made the JLabel private and have given the class a public setter method, setLabelText(String text), that allows outside classes the ability to set the JLabel's text.
The ButtonTextFieldClass could look something like:
class ButtonTextFieldClass extends JPanel {
private JTextField textField = new JTextField(10);
private JButton button = new JButton(new ButtonAction("Send Text"));
private LabelClass labelClass;
public ButtonTextFieldClass() {
setBorder(BorderFactory.createTitledBorder("Button TextField Panel"));
add(textField);
add(button);
}
// here we allow other classes to set instances of our LabelClass
public void setLabelClass(LabelClass labelClass) {
this.labelClass = labelClass;
}
// ....
I've also given the button an AbstractAction in place of an ActionListener since it is like a super ActionListener on steroids. Inside of it, I'd get the text from the JTextField and then call the LabelClass's setter method (if the variable is not null) to set the label's text:
public void actionPerformed(ActionEvent e) {
String text = textField.getText();
if (labelClass != null) {
labelClass.setLabelText(text);
}
}
Then to set everything up, in another class I'd create instances of both LabelClass and ButtonTextFieldClass, and then "hook them up" by calling the setter method:
LabelClass labelClass = new LabelClass();
ButtonTextFieldClass buttonTextFieldClass = new ButtonTextFieldClass();
buttonTextFieldClass.setLabelClass(labelClass); // set our reference
The whole thing could look like so:
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import javax.swing.*;
public class TransferData {
private static void createAndShowGui() {
LabelClass labelClass = new LabelClass();
ButtonTextFieldClass buttonTextFieldClass = new ButtonTextFieldClass();
buttonTextFieldClass.setLabelClass(labelClass); // set our reference
JPanel mainPanel = new JPanel(new GridLayout(0, 1));
mainPanel.add(buttonTextFieldClass);
mainPanel.add(labelClass);
JFrame frame = new JFrame("TransferData");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
class LabelClass extends JPanel {
private JLabel label = new JLabel("");
public LabelClass() {
setBorder(BorderFactory.createTitledBorder("Label Panel"));
add(label);
}
public void setLabelText(String text) {
label.setText(text);
}
}
class ButtonTextFieldClass extends JPanel {
private JTextField textField = new JTextField(10);
private JButton button = new JButton(new ButtonAction("Send Text"));
// one possible solution -- give this class a variable
// of the LabelClass -- but don't initialize the variable
// here, but rather do it in a setter
private LabelClass labelClass;
public ButtonTextFieldClass() {
setBorder(BorderFactory.createTitledBorder("Button TextField Panel"));
add(textField);
add(button);
}
// here we allow other classes to set instances of our LabelClass
public void setLabelClass(LabelClass labelClass) {
this.labelClass = labelClass;
}
// an AbstractAction is like a "super" ActionListener
private class ButtonAction extends AbstractAction {
public ButtonAction(String name) {
super(name); // set the button's text and actionCommand
int mnemonic = (int) name.charAt(0); // get first char
putValue(MNEMONIC_KEY, mnemonic); // set mnemonic
}
#Override
public void actionPerformed(ActionEvent e) {
String text = textField.getText();
if (labelClass != null) {
labelClass.setLabelText(text);
}
}
}
}
For simplicity's sake, I've displayed both JPanels within the same GUI, but it could work just as well if one JPanel were in one JFrame and the other within a JDialog.

using listeners with both list and button

Very new to Java, but I am slowly picking my way through things. So please be kind. I understand most things I've tried so far, and built a version of the following that uses console output, but now I'm trying to make a GUI. I tried the netbeans GUI maker, but it created so much new code that when I tried to pick through it, I got lost. I'm much better at learning by piecing new things together myself, not having an IDE generate a ton of code and then attempt to find where I want to work.
I am trying to build an window that has a list with three choices on the left side, a button in the middle that confirms your choice, and an answer output on the right. Once the button is pressed, the input from the list is read and is converted into a corresponding answer. As of right now, all I get is "We recommend... null" after selecting an option in the list. The button appears to do nothing at the moment.
I have used tutorials, hacked up others' code from online, and referenced a few books, but I'm stuck.
Here is what I have:
package diffguidegui;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
public class DiffGuideGUI extends JPanel implements ListSelectionListener {
private JList resultsTabList;
private DefaultListModel listModel;
private static final String recommendString = "Recommend a Option";
private JButton recommendButton;
private String recommendOutput;
final JLabel output = new JLabel("We recommend..." + recommendOutput);
//build list
public DiffGuideGUI () {
super(new BorderLayout());
listModel = new DefaultListModel();
listModel.addElement("A");
listModel.addElement("B");
//create the list and put it in the scroll pane
resultsTabList = new JList(listModel);
resultsTabList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
resultsTabList.setSelectedIndex(0);
//listener for user input
resultsTabList.addListSelectionListener(this);
resultsTabList.setVisibleRowCount(2);
JScrollPane listScrollPane = new JScrollPane(resultsTabList);
//build the button at the bottom to fire overall behavior
recommendButton = new JButton(recommendString);
recommendButton.setActionCommand(recommendString);
recommendButton.addActionListener(new RecommendListener());
//create a panel that uses Boxlayout for the button
JPanel buttonPane = new JPanel();
buttonPane.setLayout(new BoxLayout(buttonPane, BoxLayout.LINE_AXIS));
buttonPane.add(recommendButton);
//create a panel that uses Boxlayout for the label
JPanel outputPane = new JPanel();
outputPane.setLayout(new BoxLayout(outputPane, BoxLayout.LINE_AXIS));
outputPane.add(output);
add(listScrollPane, BorderLayout.WEST);
add(buttonPane, BorderLayout.CENTER);
add(outputPane, BorderLayout.EAST);
}
//build listener class
class RecommendListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
//build in logic for choice made here
String resultsTabChoice;
resultsTabChoice = (String)resultsTabList.getSelectedValue();
if( resultsTabChoice.equals("A")) {
recommendOutput = "One";}
else {recommendOutput = "Two";}
}
}
public void valueChanged(ListSelectionEvent e) {
if(e.getValueIsAdjusting() == false) {
if(resultsTabList.getSelectedIndex() == -1) {
recommendButton.setEnabled(false);
} else {
recommendButton.setEnabled(true);
}
}
}
//Create GUI and show it
private static void createAndShowGUI() {
JFrame frame = new JFrame("Recommend Window");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//create and set up content pane
JComponent newContentPane = new DiffGuideGUI();
newContentPane.setOpaque(true);
frame.setContentPane(newContentPane);
//display the window
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}

The button appears to do nothing at the moment.
It does something. It calculates the value for your recommendOutput varable. But you never output this value.
try the following:
//build listener class
class RecommendListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
//build in logic for choice made here
String resultsTabChoice;
resultsTabChoice = (String)resultsTabList.getSelectedValue();
if( resultsTabChoice.equals("A")) {
recommendOutput = "One";}
else {recommendOutput = "Two";}
System.out.println(recommendOutput); // <-###################
}
}
This should print the value to stdout
To put the value into your label try this instead:
output.setText(recommendOutput);

where do you set the text for the JLabel? It says "We recommend NULL" because recommenedOutput is null when the object is created. I dont see
output.setText("We recommend "+value) anywhere. You probably need output.invalidate() also. Try putting setText(String text)/invalidate() in the RecommendListener.actionPerformed() method.
output.setText("We recommend A");
output.invalidate();