Java

Introduction to Event Listeners (The Java™ Tutorials > Creating a GUI With JFC/Swing > Writing Event Listeners)[^]

30-Mar-20 22:52

Re: cannot resolve

MallardsReach30-Mar-20 23:22

30-Mar-20 23:22

Thanks for all the help, will go and look at the link that you have given.
Just realised all the examples can be downloaded and run in netbeans or using notepad++ / eclipse.
So not only can you read the tutorials you can run and walk through them.
I think I made the fundamental mistake of looking at various forums and java related sites picking up bits of code from here and there, only half of which I understand.
So I have deleted all links, and will now go and read the tutorials.
See you in about 6months time.

modified 31-Mar-20 6:10am.

Radio Button Selected

MallardsReach25-Mar-20 9:50

25-Mar-20 9:50

Below is the code for 12 radiobuttons it compiles and runs but when I test out the first 2 buttons nothing happens. I have setActionCommand in the loop for each button so What is it I've not done?

Java

ButtonGroup bgTableButtons = new ButtonGroup();

    JRadioButton[] rbTable = new JRadioButton[13];

        int y = 20;
        for (int i = 1; i < rbTable.length; i++)
            {
                rbTable[i] = new JRadioButton(Integer.toString(i) + " Times");
                rbTable[i].setActionCommand(Integer.toString(i));
                rbTable[i].setBounds(320, y, 80, 20);
                bgTableButtons.add(rbTable[i]);
                panel.add(rbTable[i]);
                y = y + 20;
            } //End of for loop

if(rbTable[1].isSelected())
{
   userText.setText("Button 1");
}
else if(rbTable[2].isSelected())
{
    userText.setText("Button 2");
} // End of if

ZurdoDev25-Mar-20 10:10

ZurdoDev

25-Mar-20 10:10

Do you have code for that implements the action command?

Social Media - A platform that makes it easier for the crazies to find each other.

Everyone is born right handed. Only the strongest overcome it.
Fight for left-handed rights and hand equality.

MallardsReach25-Mar-20 10:33

25-Mar-20 10:33

I have the following imports that's all
What other code do I need? the examles I've looked just show isSelected and that's all.

Java

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

ZurdoDev25-Mar-20 10:39

ZurdoDev

25-Mar-20 10:39

Why are you setting setActionCommand to a number?

Social Media - A platform that makes it easier for the crazies to find each other.

Everyone is born right handed. Only the strongest overcome it.
Fight for left-handed rights and hand equality.

MallardsReach25-Mar-20 11:11

25-Mar-20 11:11

Because I tried setting it to the name of the radiobutton but that didn't work either.

Java

rbTable[i].setActionCommand(Integer.toString(i) + " Times");

ZurdoDev25-Mar-20 12:19

ZurdoDev

25-Mar-20 12:19

Do you know what the command is for?

Social Media - A platform that makes it easier for the crazies to find each other.

Everyone is born right handed. Only the strongest overcome it.
Fight for left-handed rights and hand equality.

Richard MacCutchan26-Mar-20 0:16

26-Mar-20 0:16

That is not the way to do it I am afraid. Visual components use event handlers which are signalled when the events (e.g. pushing a button) occurs. So you need to use the Button (Java Platform SE 7 ) addActionListener[^] method so your code gets called at the relevant time.

I would again strongly suggest you go to The Java™ Tutorials[^] and work through them a few times. Trying to learn a language and framework by posting questions here (or any other forum) will take you much longer to get to where you want.

MallardsReach26-Mar-20 0:28

26-Mar-20 0:28

Thanks Richard
I have and do look at the Java Tutorials but don't always find them helpful even though they explain the concepts of components.
I did eventually figure it out, the code is below for anyone else to look through,

Java

ItemListener itemListener = new ItemListener() {
    public void itemStateChanged(ItemEvent itemEvent) {
        AbstractButton aButton = (AbstractButton)itemEvent.getSource();
            int state = itemEvent.getStateChange();
            String name = aButton.getText();
        for (int i = 1; i < rbTable.length; i++)
        {
            if (state == ItemEvent.SELECTED) {
                if (name.equals(rbTable[i].getText())) {
                    userText.setText(rbTable[i].getText());
                }

            }
        }
    }
};

Richard MacCutchan26-Mar-20 0:36

26-Mar-20 0:36

MallardsReach wrote:
don't always find them helpful even though they explain the concepts of components.

What about all the sample code that's included? Seriously, you really should persevere with them. They teach things in a structured order and you get all the basic concepts well established before moving on to the more advanced stuff. I used the published version of these years ago when I first started working in Java, and have gone back and repeated the online versions a number of times.

MallardsReach26-Mar-20 2:55

26-Mar-20 2:55

Hi Richard,
Can't argue and have no wish to, with the points you make about the sample code,
The thing is they are stand alone ie
Here's a method, here's how to call it.
Here' some radio buttons, here's how to find the one selected.

And they work fine the problem is when your project gets more added to it and includes many components and then it's trying to get them to work with each other.
I am going to get 'Java: The Complete Reference, Eleventh Edition' as soon as things get back to normal.
Until then I have to rely on the tutorials and forums to guide me.

MallardsReach26-Mar-20 4:15

26-Mar-20 4:15

Talk about making things complicated!
Here is the final code, no user defined method was needed, I just had to place the results for pressing a button in the 'itemStateChanged method'

Java

ItemListener itemListener = new ItemListener() {
    public void itemStateChanged(ItemEvent itemEvent) {
        AbstractButton aButton = (AbstractButton)itemEvent.getSource();
            int state = itemEvent.getStateChange();
            String name = aButton.getText();
        for (int i = 1; i < rbTable.length; i++)
        {
            if (state == ItemEvent.SELECTED) {
                if (name.equals(rbTable[i].getText())) {
                    displayTable.setText(""); //Clear the displayTable
                    int firstNum, answerNum;
                    for (firstNum = 1; firstNum <=12; firstNum ++)
                    {
                        answerNum = firstNum * i;
                        displayTable.append(" " + firstNum + " x " + i + " = " + answerNum +"\n");
                    }

                }
            }
        }
    }
};

User defined Method

MallardsReach24-Mar-20 2:56

24-Mar-20 2:56

Looked at many examples of Method and they all seem easy until I start to place them in my code.
No matter where I insert the method or how I rewrite it I still get a problem.
Below is my Method followed by my code. What am I not doing?

Java

void getSecond(int secondNum){
 displayTable.setText("\n"); //Clear the displayTable
 int firstNum, answerNum;
     for (firstNum = 1; firstNum <=12; firstNum ++){
         answerNum = firstNum * secondNum;
         displayTable.append(firstNum + " x " + secondNum + " = " + answerNum +"\n");
      }

Java

import javax.swing.*;
import java.awt.Color;
import java.awt.Font;
import javax.swing.BorderFactory; 
import javax.swing.border.Border;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class MyTables
{

	public static void main(String[] args) 
	{
		JFrame frame = new JFrame("Tables"); // Creating instance of JFrame
        frame.setSize(800, 600); // Setting the width and height of frame
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
		JPanel panel = new JPanel(); //Creating panel. Inside panels we can add textfields, buttons and other components.
		panel.setBorder(BorderFactory.createLineBorder(Color.RED));
        frame.add(panel); // Add panel to frame
        placeComponents(panel);  //Call user defined method for adding components to the panel.
		frame.setVisible(true); // Setting the frame visibility to true
    }

	private static void placeComponents(JPanel panel) 
	{
			panel.setLayout(null);
			JTextArea displayTable = new JTextArea("Text Area");
			displayTable.setEditable(false);
			displayTable.setColumns(20);
			displayTable.setFont(new Font("Times New Roman", 1, 14));
			displayTable.setLineWrap(true);
			displayTable.setRows(14);
			displayTable.setWrapStyleWord(true);
			displayTable.setBounds(200,20,230,260); 
			displayTable.setBorder(BorderFactory.createLineBorder(Color.GREEN));
			displayTable.setMaximumSize(new java.awt.Dimension(5, 22));
			panel.add(displayTable);
			
			JLabel userLabel = new JLabel("Enter a Number");  // Creating JLabel
			userLabel.setHorizontalAlignment(SwingConstants.CENTER);
			userLabel.setFont(new Font("Verdana", Font.ITALIC, 16)); //set font
			userLabel.setBounds(10,20,180,25); // Specifies the location and size of component. (x,y,x1,y1)
			userLabel.setBorder(BorderFactory.createLineBorder(Color.BLUE));	
			panel.add(userLabel); // Add Label to panel

			JTextField userText = new JTextField(20); //Create a textfield
			userText.setBounds(10,50,165,25);
			panel.add(userText); // Add TextField to pane

			JButton loginButton = new JButton("Enter"); // Create button
			loginButton.setBounds(10, 80, 80, 25);
			panel.add(loginButton); // Add loginButton to panel
			
			 
		loginButton.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent e)
				{
					//getSecond(6);
					displayTable.setText("Button Pressed");
				}

		});
    }		
}

Richard MacCutchan24-Mar-20 4:18

24-Mar-20 4:18

MallardsReach wrote:
I still get a problem.

That is one of the most common reports that we see here, and also the most useless. Unless you tell us exactly what the problem is (including exact error messages), and where it occurs, then we can do very little. Please try to help us to help you.

MallardsReach24-Mar-20 7:39

24-Mar-20 7:39

Sorry Richard, honestly thought I had given the error.
If I place the code here

Java

public class MyTables
{
       void getSecond(int secondNum){
        displayTable.setText("\n"); //Clear the displayTable 
        int firstNum, answerNum;
            for (firstNum = 1; firstNum <=12; firstNum ++){
                answerNum = firstNum * secondNum;
                displayTable.append(firstNum + " x " + secondNum + " = " + answerNum +"\n");
             }
	public static void main(String[] args)

I get this message

Quote:
c:\Java>javac MyTables.java
MyTables.java:18: error: illegal start of expression
public static void main(String[] args)
^
1 error

If I put it at the end

Java

loginButton.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent e)
				{
					//getSecond(6);
					displayTable.setText("Button Pressed");
				}
				       void getSecond(int secondNum){
        displayTable.setText("\n"); //Clear the displayTable 
        int firstNum, answerNum;
            for (firstNum = 1; firstNum <=12; firstNum ++){
                answerNum = firstNum * secondNum;
                displayTable.append(firstNum + " x " + secondNum + " = " + answerNum +"\n");
             }

		});
    }		
}

I get 3 error messages

Quote:
c:\Java>javac MyTables.java
MyTables.java:69: error: illegal start of type
});
^
MyTables.java:70: error: ')' expected
}
^
MyTables.java:71: error: reached end of file while parsing
}
^
3 errors

Richard MacCutchan24-Mar-20 7:44

24-Mar-20 7:44

Look at the code, it has two opening brace characters ({), one for the method, and one for the for loop. But it only has one closing brace, for the for loop. So you just need to add the one that closes the method block.

MallardsReach24-Mar-20 8:29

24-Mar-20 8:29

That's done it, although I am annoyed as I knew the curly bracket was missing but when I added it I got different errors.
After your reply I removed the method placed it in a new page and added the bracket so that it had 2 opening and 2 closing, placed it back in my project and it worked.
I do remember that every opening ( or { had to have a matching one closing.
Can now carry on with the project.
Thank you

Richard MacCutchan24-Mar-20 10:16

24-Mar-20 10:16

The thing to remember is when you start any code block is to add the braces first. You can then fill in the actual code afterwards:

Java

int someMethod(int parameter)
{
    // TODO: the details must be added here
}
int someOtherMethod(int parameter)
{
    while (some expression)
    {
         // TODO: more details required
    }
    if (some boolean expression
    {
        // TODO: check some stuff
    }
}

But always remember, making mistakes is how we all learned ...

MallardsReach24-Mar-20 22:17

24-Mar-20 22:17

Thanks Richard that is a good piece of advice that I will remember.

But always remember, making mistakes is how we all learned ...

And this gives me some encouragement as it seems I'm making quite a few.

JTextArea

MallardsReach23-Mar-20 0:48

23-Mar-20 0:48

OK, so I'm back to using notepad++ in a panel I have a TextBox, Label and Buton all of which show but I have a TextArea that doesn't show, tried various ways but nothing has worked.

Java

private static void placeComponents(JPanel panel)
{
        panel.setLayout(null);
        JTextArea displayTable = new JTextArea("Text Area");
        displayTable.setEditable(false);
        displayTable.setColumns(20);
        displayTable.setFont(new Font("Times New Roman", 1, 14));
        displayTable.setLineWrap(true);
        displayTable.setRows(14);
        displayTable.setWrapStyleWord(true);
        displayTable.setBorder(BorderFactory.createLineBorder(Color.GREEN));
        displayTable.setMaximumSize(new java.awt.Dimension(5, 22));
        panel.add(displayTable);

Re: JTextArea

Richard MacCutchan23-Mar-20 0:54

Calling a Method at run time

23-Mar-20 0:54

Take a look at this example: Using Text Components (The Java™ Tutorials, Creating a GUI With JFC/Swing)[^]

MallardsReach21-Mar-20 22:32

Re: Calling a Method at run time

21-Mar-20 22:32

I am using an example code that I found line JavaPoint which works and does what I would want it to do, so I thought I would use it in my Netbeans project.
It took a while to figure out what did what as there were no comments and obscure naming eg buttons name is 1.
I now have it working and have renamed things there is one problem I can't figure and it's a call to a method called set()
The program starts with a question and 4 possible radiobutton answers you select an answer then click button next which shows question 2.
For some reason It doesn't show question 1 when the form first loads. Tried various things but none worked for me.
The Next Button Code:

Java

private void btnNextActionPerformed(java.awt.event.ActionEvent evt) {
    if(check()) // Check answer
        count=count+1;
    current++;
        set();  //Next question
if(current==9)
{
     JOptionPane.showMessageDialog(this,"Correct Answers = "+count);
     btnNext.setEnabled(false);
        //b2.setText("Result");
}
}

First section of the set() Method code

Java

void set()
	{
		rbSetQuestion.setSelected(true);
		if(current==0)
		{
			lblQuestions.setText("Question1: Which one among these is not a datatype");
			rbChoice_1.setText("int");rbChoice_2.setText("Float");rbChoice_3.setText("boolean");rbChoice_4.setText("char");	
		}
		if(current==1)
		{
			lblQuestions.setText("Question2: Which class is available to all the class automatically");
			rbChoice_1.setText("Swing");rbChoice_2.setText("Applet");rbChoice_3.setText("Object");rbChoice_4.setText("ActionEvent");
		}

Richard MacCutchan21-Mar-20 23:29