Java

10-Apr-20 22:17

There are thousands of helpful tutorials online. But you have probably left it too late to make use of any of them.

cannot resolve

MallardsReach30-Mar-20 4:32

30-Mar-20 4:32

Below is the full code I am using but I get the following error messages showing at the start of my code

Quote:
Multiple markers at this line
- txtNumOne cannot be resolved
- txtNumTwo cannot be resolved

and

Quote:
lblDPAnswer cannot be resolved

Java

package components;
import java.awt.event.*;
import javax.swing.*;
import java.awt.Color;
import java.awt.Font;
import javax.swing.BorderFactory; 
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class MathsLesson
{	 	 
      String strAnswer;
       
    	void showAnswer(int dPlaces){
    Double numAnswer; String strAnswer; 
    numAnswer = (Double.parseDouble(txtNumOne.getText()))* (Double.parseDouble(txtNumTwo.getText()));
    strAnswer = String.format("%,." + dPlaces + "f", numAnswer); 
    lblDPAnswer.setText(strAnswer);
   
 }
	
	public MathsLesson() 
	{		
		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(javax.swing.BorderFactory.createEtchedBorder(javax.swing.border.EtchedBorder.RAISED, new java.awt.Color(255, 51, 51), new java.awt.Color(153, 0, 51)));
		frame.add(panel); // Add panel to frame
       	frame.setVisible(true); // Setting the frame visibility to true
			panel.setLayout(null);	
		    JPanel tablepanel = new JPanel();
			tablepanel.setLayout(null);
			tablepanel.setBounds(10,20,320,300);
			tablepanel.setBorder(BorderFactory.createTitledBorder(BorderFactory.createEtchedBorder(), "Times Tables"));
			tablepanel.setOpaque(false); 
			panel.add(tablepanel);
			
			panel.setLayout(null);	
		    JPanel decimalpanel = new JPanel();
			decimalpanel.setLayout(null);
			decimalpanel.setBounds(10,320,320,100);
			decimalpanel.setBorder(BorderFactory.createTitledBorder(BorderFactory.createEtchedBorder(), "Decimal Places"));
			decimalpanel.setOpaque(false); 
			panel.add(decimalpanel);
			
			JTextArea displayTable = new JTextArea();
			displayTable.setEditable(false);
			displayTable.setFont(new java.awt.Font("Times New Roman", 0, 18));
			displayTable.setText("Choose a button on the right to view the table you want to see");
			displayTable.setLineWrap(true);
			displayTable.setWrapStyleWord(true);
			displayTable.setBounds(10,20,150,260); 
			displayTable.setBorder(BorderFactory.createLineBorder(Color.GREEN));
			tablepanel.add(displayTable);
			
			//ImageIcon imageIcon = new ImageIcon("images/bird.gif");
			JLabel userLabel = new JLabel();  // Creating JLabel
			userLabel.setIcon(new ImageIcon("images/bird.gif"));
			userLabel.setHorizontalAlignment(SwingConstants.CENTER);
			userLabel.setFont(new Font("Verdana", Font.ITALIC, 16)); //set font
			userLabel.setBounds(500,20,125,125); 
			userLabel.setBorder(BorderFactory.createLineBorder(Color.BLUE));	
			panel.add(userLabel); // Add Label to panel
			
			JTextField txtNumOne = new JTextField(20);
			txtNumOne.setBounds(15,350,70,25);
			panel.add(txtNumOne); // Add TextField to panel
			
			JTextField txtNumTwo = new JTextField(20);
			txtNumTwo.setBounds(130,350,70,25);
			panel.add(txtNumTwo); // Add TextField to panel
			
			JLabel lblDPAnswer = new JLabel();  // Creating JLabel
			lblDPAnswer.setHorizontalAlignment(SwingConstants.CENTER);
			lblDPAnswer.setBounds(220,350,100,25); 
	        lblDPAnswer.setBackground(new java.awt.Color(255, 255, 255));
	        lblDPAnswer.setFont(new java.awt.Font("Times New Roman", 1, 18)); // NOI18N
	        lblDPAnswer.setBorder(javax.swing.BorderFactory.createLineBorder(new java.awt.Color(0, 0, 0)));
	        lblDPAnswer.setOpaque(true);
			panel.add(lblDPAnswer); // Add Label to panel
			
			ButtonGroup bgDecimalButtons = new ButtonGroup();
			JRadioButton rbOneDecimal = new JRadioButton("1 DP");
			bgDecimalButtons.add(rbOneDecimal);
			rbOneDecimal.setFont(new java.awt.Font("Times New Roman", 0, 14));
			rbOneDecimal.setBounds(15, 380, 60, 30);
			panel.add(rbOneDecimal);
			
			JRadioButton rbTwoDecimal = new JRadioButton("2 DP");
			bgDecimalButtons.add(rbTwoDecimal);
			rbTwoDecimal.setFont(new java.awt.Font("Times New Roman", 0, 14));
			rbTwoDecimal.setBounds(85, 380, 60, 30);
			panel.add(rbTwoDecimal);
			
			JRadioButton rbThreeDecimal = new JRadioButton("3 DP");
			bgDecimalButtons.add(rbThreeDecimal);
			rbThreeDecimal.setFont(new java.awt.Font("Times New Roman", 0, 14));
			rbThreeDecimal.setBounds(155, 380, 60, 30);
			panel.add(rbThreeDecimal);
			
			JButton btnSum = new JButton("Enter"); // Create button
			btnSum.setBounds(220, 380, 100, 25);
	        btnSum.setFont(new java.awt.Font("Times New Roman", 1, 36));
	        btnSum.setText("=");
	        btnSum.setBorder(javax.swing.BorderFactory.createBevelBorder(javax.swing.border.BevelBorder.RAISED));
			panel.add(btnSum); // Add btnSum to panel
		
			
			JRadioButton[] rbTable = new JRadioButton[13]; //set an array for 12 radioButtons			
			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
								tablepanel.setBorder(BorderFactory.createTitledBorder(BorderFactory.createEtchedBorder(),+ i + " Times Table"));								
								int firstNum, answerNum;
								for (firstNum = 1; firstNum <=12; firstNum ++)
								{
									answerNum = firstNum * i;
									displayTable.append("  " + firstNum + " x " + i + " = " + answerNum +"\n");
								}
				
							}
						}
					}
				}  
			};
			
			    ButtonGroup bgTableButtons = new ButtonGroup();
				int y = 50, x = 165; //Add 12 tables radio buttons
				for (int i = 1; i < rbTable.length; i++)
					{
						rbTable[i] = new JRadioButton("X  " + Integer.toString(i));
						rbTable[i].setFont(new java.awt.Font("Times New Roman", 0, 18));
						rbTable[i].addItemListener(itemListener);
						rbTable[i].setBounds(x, y, 70, 20);
						if(i == 6){
						x = 235;
						y = 20;
						}
						bgTableButtons.add(rbTable[i]);
						tablepanel.add(rbTable[i]);
						y = y + 30;
					}
				
			      rbOneDecimal.addActionListener(new ActionListener() {
				         public void actionPerformed(ActionEvent e) {
				        	 lblDPAnswer.setText("Button 1");
				      				        	}
				      });
			      rbTwoDecimal.addActionListener(new ActionListener() {
				         public void actionPerformed(ActionEvent e) {
				        	 lblDPAnswer.setText("Button 2"); 
				         }
				      });
			      
			      rbThreeDecimal.addActionListener(new ActionListener() {
				         public void actionPerformed(ActionEvent e) {   
				        	 lblDPAnswer.setText("Button 3");
				         }
				      });
			      btnSum.addActionListener(new ActionListener() {
				         public void actionPerformed(ActionEvent e) {
				        	  showAnswer(0); //call method
				        	 }
				      });
	}//End of Constructor
		
	public static void main(String[] args) 
	{
        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new MathsLesson();	
                
            }
        });
     } //End of void main
            
} // End of Class

Richard MacCutchan30-Mar-20 4:50

30-Mar-20 4:50

You are creating local variables in one method, and then trying to access them from other methods. You need to understand the scope rules, i.e whether variables are local or not. So txtNumOne and txtNumTwo should be class level variables. Alternatively they could be passed as parameters to the showAnswer method.

You have a potential mistake in the following code:

Java

     String strAnswer; // this is a class level variable, i.e. visible to every method in the class

   void showAnswer(int dPlaces){
       Double numAnswer;
       // this has the same name as the class level variable,
       // but is only visible inside this method, so a possible conflict
       String strAnswer;
       // don't write compound statements like this, they are much harder to diagnose when things go wrong
       numAnswer = (Double.parseDouble(txtNumOne.getText()))* (Double.parseDouble(txtNumTwo.getText()));
       strAnswer = String.format("%,." + dPlaces + "f", numAnswer);
       lblDPAnswer.setText(strAnswer);

}

MallardsReach30-Mar-20 7:29

30-Mar-20 7:29

Thanks Richard after many hours of head scratching and internet searching I think I have it.
Below is the class level variables and the method showAnswer.

Java

 // Variables declaration
        double decNum1, decNum2, decAnswer; // class level available to all
        String strAnswer;
   // End of variables declaration

 void showAnswer(int dPlaces){
     Double numAnswer;
     numAnswer = decNum1 * decNum2;
     strAnswer = String.format("%,." + dPlaces + "f", numAnswer);
}

And below is the 3 radiobuttons and the sum button that call the method when clicked.

Java

rbOneDecimal.addActionListener(new ActionListener() {
       public void actionPerformed(ActionEvent e) {
           decNum1 = Double.parseDouble(txtNumOne.getText());
           decNum2 = Double.parseDouble(txtNumTwo.getText());
            showAnswer(1); //call method
            lblDPAnswer.setText(strAnswer);
                              }
    });
rbTwoDecimal.addActionListener(new ActionListener() {
       public void actionPerformed(ActionEvent e) {
           decNum1 = Double.parseDouble(txtNumOne.getText());
           decNum2 = Double.parseDouble(txtNumTwo.getText());
            showAnswer(2); //call method
            lblDPAnswer.setText(strAnswer);
       }
    });

rbThreeDecimal.addActionListener(new ActionListener() {
       public void actionPerformed(ActionEvent e) {
           decNum1 = Double.parseDouble(txtNumOne.getText());
           decNum2 = Double.parseDouble(txtNumTwo.getText());
            showAnswer(3); //call method
            lblDPAnswer.setText(strAnswer);
       }
    });
btnSum.addActionListener(new ActionListener() {
       public void actionPerformed(ActionEvent e) {
           decNum1 = Double.parseDouble(txtNumOne.getText());
           decNum2 = Double.parseDouble(txtNumTwo.getText());
            showAnswer(0); //call method
            lblDPAnswer.setText(strAnswer);
           }
    });

Could it be done a better way? I seem to be repeating these 2 lines.

Java

decNum1 = Double.parseDouble(txtNumOne.getText());
decNum2 = Double.parseDouble(txtNumTwo.getText());

Richard MacCutchan30-Mar-20 7:45

30-Mar-20 7:45

Rather than make these variables at class level, make them parameters to showAnswer (actually calcAnswer would be a better name) method. And the final result shoud be the return value. Something like:

Java

String showAnswer(double decNum1, double decNum2, int dPlaces){
     Double numAnswer = decNum1 * decNum2;
     String strAnswer = String.format("%,." + dPlaces + "f", numAnswer);

    return strAnswer;
}

That keeps everything neatly within the method.

You can reduce all the duplication by using the same handler for all the buttons.

Java

public void actionPerformed(ActionEvent e) {
    int numDecimals = // get the number from the button text

    double decNum1 = Double.parseDouble(txtNumOne.getText());
    double decNum2 = Double.parseDouble(txtNumTwo.getText());
    String strResult = showAnswer(decNum1, decNum2, numDecimals); //call method
    lblDPAnswer.setText(strResult);
}

Then add that to each button:

Java

rbOneDecimal.addActionListener(actionPerformed);
rbTwoDecimal.addActionListener(actionPerformed);

You may need to check the syntax requirements for these last two/three items

MallardsReach30-Mar-20 11:32

30-Mar-20 11:32

Thought it wouldn't work as easy as that. Frown | :(

errors for the actionPerformed method,

Quote:
Multiple markers at this line
- void is an invalid type for the variable actionPerformed
- Syntax error on token "(", ; expected
- Syntax error on token ")", ; expected

errors for all the buttons .addActionListener(ActionPerformed);

Quote:
ActionPerformed cannot be resolved to a variable

Richard MacCutchan30-Mar-20 22:34

30-Mar-20 22:34

I hesitate to say this yet again, but please go to The Java™ Tutorials[^] and study the language properly. You are not going to learn it piecemeal by posting questions here, as each issue is looked at in isolation. You need to follow a structured learning path to get a full understanding of, not just the language, but its framework support as well.

Richard MacCutchan30-Mar-20 23:52

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

30-Mar-20 23:52

MallardsReach31-Mar-20 0:22

31-Mar-20 0:22

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 10:50

25-Mar-20 10:50

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 11:10

ZurdoDev

25-Mar-20 11:10

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 11:33

25-Mar-20 11:33

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 11:39

ZurdoDev

25-Mar-20 11:39

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 12:11

25-Mar-20 12:11

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 13:19

ZurdoDev

25-Mar-20 13:19

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 1:16

26-Mar-20 1:16

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 1:28

26-Mar-20 1:28

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 1:36

26-Mar-20 1:36

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 3:55

26-Mar-20 3:55

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 5:15

26-Mar-20 5:15

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 3:56

24-Mar-20 3:56

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");
				}

		});
    }		
}

Re: User defined Method

Richard MacCutchan24-Mar-20 5:18