We Keep Coding

How to make button in one class affect text area in another?

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();
}
}

error: illegal start of expression 1 error

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import java.lang.*;
import java.util.*;
public class Life {
public static void main (String[] args){
JFrame frame = new JFrame("Interest Calculator");
frame.setVisible(true);
frame.setSize(300,100);
frame.setBackground(Color.magenta);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new JPanel();
frame.add(panel);
JButton button = new JButton("Simple Interest");
panel.add(button);
button.addActionListener (new Action1());
JButton button2 = new JButton("Compound Interest");
panel.add(button2);
button2.addActionListener (new Action2());
}
static class Action1 implements ActionListener {
public void actionPerformed (ActionEvent e) {
JFrame frame2 = new JFrame("Simple");
frame2.setVisible(true);
frame2.setSize(300,100);
JPanel panel = new JPanel();
frame2.add(panel);
JButton button = new JButton("Ordinary");
panel.add(button);
button.addActionListener (new Ordinary());
JButton button2 = new JButton("Exact");
panel.add(button2);
button2.addActionListener (new Exact());
}
}
static class Action2 implements ActionListener {
public void actionPerformed (ActionEvent e) {
JFrame frame3 = new JFrame("Compound Interest");
frame3.setVisible(true);
frame3.setSize(300,100);
JPanel panel = new JPanel();
frame3.add(panel);
JButton button = new JButton("Compounded");
panel.add(button);
JButton button2 = new JButton("Continously");
panel.add(button2);
}
}
static class Ordinary implements ActionListener {
public void actionPerformed (ActionEvent e) {
JFrame frame4 = new JFrame("Simple");
frame4.setVisible(true);
frame4.setSize(300,100);
JPanel panel = new JPanel();
frame4.add(panel);
JButton button = new JButton("Approximate");
panel.add(button);
button.addActionListener (new Approximate());
JButton button2 = new JButton("Actual");
panel.add(button2);
}
}
static class Exact implements ActionListener {
public void actionPerformed (ActionEvent e) {
JFrame frame5 = new JFrame("Exact");
frame5.setVisible(true);
frame5.setSize(300,100);
JPanel panel = new JPanel();
frame5.add(panel);
JButton button = new JButton("Approximate");
panel.add(button);
JButton button2 = new JButton("Actual");
panel.add(button2);
}
}
static class Approximate implements ActionListener {
public void actionPerformed (ActionEvent e) {
JFrame frame6 = new JFrame("Simple");
frame6.setVisible(true);
frame6.setSize(300,100);
JPanel panel = new JPanel();
frame6.add(panel);
frame6.setVisible(true);
frame6.setSize(300,300);
frame6.setLayout(null);
frame6.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JTextField P = new JTextField();
panel.add(P);
P.setText("Enter Principal");
JTextField r = new JTextField();
panel.add(r);
r.setText("Enter Rate");
JTextField t = new JTextField();
panel.add(t);
t.setText("Enter Year");
JButton button = new JButton("Calculate");
panel.add(button);
button.addActionListener (new button());
static class button implements ActionListener {
public void actionPerformed (ActionEvent e) {
float P,r,t,result ;
P = Float.parseFloat(P.getText());
r = Float.parseFloat(r.getText());
t = Float.parseFloat(t.getText());
result = P*r/100*t/360;
button.setText(String.valueof(result));
}
}
}
}
}
So this is my code to create a compound calculator but I have a problem it is the illegal start of expression.please help me for my project.

Below is partially fixed part of the code which causes problems. Next time include full error code, and try to show only relevant part of the code.
ActionListener listener = new ActionListener() {
public void actionPerformed (ActionEvent e) {
float P,r,t,result ;
//P = Float.parseFloat(P.getText()); // P makes no sens here - its float !!! and uninitialized
//r = Float.parseFloat(r.getText()); // same for r
//t = Float.parseFloat(t.getText()); // same for t
result = P*r/100*t/360;
button.setText(String.valueOf(result));
}
};
button.addActionListener (listener);

Swing Number Format Exception

For some reason the AddListener class below doesn't work, and I keep getting a number format exception. Could anyone please tell me the reason for this. It seems to me as if it should work.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class BabyCalculator extends JFrame {
JFrame theFrame = this;
JTextField addField; // Declaring this here so that you can access the variable from other places. MAKE SURE TO NOT DECLARE THIS AGAIN IN THE CONSTRUCTOR
JTextField totalField;
public BabyCalculator() {
//You set this up so that you can refer to the frame using the inner class below.
setDefaultCloseOperation(EXIT_ON_CLOSE);
setName("Baby Calculator");
setLayout(new GridLayout(3, 0));
//add
JLabel addLabel = new JLabel("Amount to add:");
addField = new JTextField(10);
JButton addButton = new JButton("add");
addButton.addActionListener(new AddListener());
//multiply
JLabel multiplyLabel = new JLabel("Amount to multiply:");
JTextField multiplyField = new JTextField(10);
JButton multiplyButton = new JButton("multiply");
//total
JLabel totalLabel = new JLabel("Total");
totalField = new JTextField(10);
totalField.setEditable(false);
JButton stopButton = new JButton("Stop");
stopButton.addActionListener(new StopListener());
//Create Panels
JPanel topRow = new JPanel(new BorderLayout());
JPanel middleRow = new JPanel(new BorderLayout());
JPanel bottomRow = new JPanel(new FlowLayout());
//Add the top Row
topRow.add(addLabel, BorderLayout.WEST);
topRow.add(addField, BorderLayout.CENTER);
topRow.add(addButton, BorderLayout.EAST);
add(topRow);
middleRow.add(multiplyLabel, BorderLayout.WEST);
middleRow.add(multiplyField, BorderLayout.CENTER);
middleRow.add(multiplyButton, BorderLayout.EAST);
add(middleRow);
bottomRow.add(totalLabel);
bottomRow.add(totalField);
bottomRow.add(stopButton);
add(bottomRow);
pack();
setVisible(true);
}
public class AddListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
String addFieldText = addField.getText();
String totalFieldText = totalField.getText();
double addAmount = Double.parseDouble(addFieldText);
double total = Double.parseDouble(totalFieldText);
total += addAmount;
totalField.setText(total + "");
}
}
//end class AddListener
public class StopListener implements ActionListener {//this is an inner class
public void actionPerformed(ActionEvent e) {
JOptionPane.showMessageDialog(theFrame, "You Clicked the stop button");
}//end class StopListener
}
public static void main(String[] args) {
JFrame newFrame = new BabyCalculator();
}
}
Note: The problem in the code is definitely related to the AddListener. Whenever I click the add button in the GUI I get an exception.

The problem is with the totalFieldText, it's default value is blank, meaning that when you try and convert to a double value, it causes a NumberFormatException
Try giving it a default value of 0, for example
totalField = new JTextField("0", 10);
You might also like to take a look at How to Use Spinners and How to Use Formatted Text Fields which will make your life easier

change JLabel of a panel depending on Jbutton of another panel in the same Jframe

I have constructed a class for the JPanel with several JButtons.Inside this class I want to construct another JPanel with JLabels that will change depending on the actionPerformed on the JButtons of the first JPanel.Finally, I want to add these 2 panels on the same Jframe. Can all these be done within the class of the first Panel?Otherwise, which is a better approach for this problem?

Yes, you can. One way you could accomplish this is with anonymous inner classes (saves keystrokes):
import java.awt.BorderLayout;
import java.awt.event.*;
import javax.swing.*;
public class Foo {
JLabel one;
JLabel two;
public static void main(String[] args) {
(new Foo()).go();
}
public void go() {
JFrame frame = new JFrame("Test");
// Panel with buttons
JPanel buttonPanel = new JPanel();
JButton changeOne = new JButton("Change One");
changeOne.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
one.setText("New text for one");
}
}
buttonPanel.add(changeOne);
JButton changeTwo = new JButton("Change Two");
changeTwo.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
two.setText("New text for two");
}
}
buttonPanel.add(changeTwo);
frame.add(buttonPanel, BorderLayout.NORTH);
// Panel with labels
JPanel labelPanel = new JLabel();
one = new JLabel("One");
labelPanel.add(one);
two = new JLabel("Two");
labelPanel.add(two);
// Set up the frame
frame.add(labelPanel, BorderLayout.SOUTH);
frame.setBounds(50, 50, 500, 500);
frame.setDefaultCloseAction(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}

how can I make this class an applet

I have the following class which is a simple gui, and I would like to make it an applet so it can be displayed in the browser. I know how to embed the code into an html page(got that done)... but how can make my class an applet? Also, I assuming I don't need a web server just to display the applet in my browser...
package tester1;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class PanelTest implements ActionListener {
JFrame frame;
JLabel inputLabel;
JLabel outputLabel;
JLabel outputHidden;
JTextField inputText;
JButton button;
JButton clear;
JButton about;
public PanelTest() {
frame = new JFrame("User Name");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new GridLayout(3, 2, 10, 10));
//creating first row
JPanel row1 = new JPanel();
inputLabel = new JLabel("Your Name");
inputText = new JTextField(15);
// FlowLayout flow1 = new FlowLayout(FlowLayout.CENTER, 10, 10);
// row1.setLayout(flow1);
row1.add(inputLabel);
row1.add(inputText);
frame.add(row1);
//creating second row
JPanel row2 = new JPanel();
button = new JButton("Display");
clear = new JButton("Clear");
about = new JButton("About");
button.addActionListener(this);
clear.addActionListener(this);
about.addActionListener(new displayAbout());
row2.add(button);
row2.add(clear);
row2.add(about);
frame.add(row2);
//creating third row
JPanel row3 = new JPanel();
outputLabel = new JLabel("Output:", JLabel.LEFT);
outputHidden = new JLabel("", JLabel.RIGHT);
// FlowLayout flow2 = new FlowLayout(FlowLayout.CENTER, 10, 10);
// row3.setLayout(flow2);
row3.add(outputLabel);
row3.add(outputHidden);
frame.add(row3);
frame.pack();
frame.setVisible(true);
}
//same method listen for two different events
#Override
public void actionPerformed(ActionEvent e) {
String command = e.getActionCommand();
if(command.equals("Display")) {
outputHidden.setText(inputText.getText());
}
if(command.equals("Clear")) {
outputHidden.setText("");
inputText.setText("");
}
}
//another way to listen for events
class displayAbout implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
JOptionPane.showMessageDialog(frame, "Username 1.1 \n by Jorge L. Vazquez");
}
}
public static void main(String[] args) {
PanelTest frameTest = new PanelTest();
}
}

Use a JApplet rather than a JFrame. Make sure you read the relevant Java Tutorial, which covers the applet lifecycle methods like init, start, stop, and destroy.
As a side note, you should not be building your UI outside of the event dispatch thread.

Use a JApplet instead of a JFrame like veer said, but you must also remove frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);, frame.pack();, and frame.setVisible(true);
Also, replace main(String[] args) with init().