Thread: action listener not working help

Can you explain what "not working" means?
If there are errors, copy the full text and paste it here.
If the output is wrong, copy and paste the output and explain what is wrong.

Please edit your post and wrap your code with
[code=java]
<YOUR CODE HERE>
[/code]
to get highlighting and preserve formatting.


BTW the poorly named variables make this code very hard to read and understand.

Can you explain what "not working" means?

now getting a null pointer exception at 1)q.start() and 2)f1.add(panel1)

Check if the variables: q and f1 have null values causing the NPE. If they do, backtrack in the code to find out why those variables do not have valid values.

Please copy the full text of the error messages and paste it here.

So i managed to get your panel to display and i see what you mean by your button not doing anything. It is getting into the action listener just fine.

#1 Rename your class with a capital letter in front. Class names should start with capitals and objects should have lower case. Google "java camel case" if you need any pointers
#2 Problems with your GUI.
---f1 is not necessary. The class extends jframe so that is your frame. Update its information using "this.setSize()" and so on.
---In start() make sure you add all three panels not just panel1. Remember it will be "this.add()"
---Suggestion, make one "init()" function that calls all of your init stuff so you dont have to do it in the main function.
#3 Your action listener. Definitely find a better way of going about this. Those nested switch statements are crazy!
---Why are your case statements going to m1, m2, m3? They just clear the frame and add a panel back in, that is where your code is breaking.

I suggest you add a few System.out.println("Code got here"); lines so you know that you are getting into certain sections. Then clean up that action listener and if you still need help let us know wha tit is actually supposed to be doing.

--- Update ---

I lied, a JFrame can only hold one JPanel. You need to make a main JPanel to hold everything else. So if you change f1 to a JPanel and make sure you add f1 to "this" then you should be good.

--- Update ---

Just so you know, I've got your program working and converting. I'm not going to give you the code or you'll learn nothing. I will however work with you to get it working. Feel free to message me or IM me and we can work through this. We'll have you up and running by the end of the evening!

I would recomend once you have it working go back and modify some stuff to make it a little more professional. For instance, look into radio buttons instead of the buttons for the scales. Your current program has no way of informing you what scale you have selected. Even having a label that states what each scale is would be beneficial. Then you can work on changing the way you are referencing buttons in your action listener. Maybe even make a couple separate action listeners for each panel as they each do independent things.

a JFrame can only hold one JPanel

Not sure what that means. You'll have to explain what you mean.
JFrame has a container as its content pane that extends the Container class which can hold many other components. Their positioning on the container is controlled by the layout manager it uses.

You're right norm, you can use the content pane. Been forever since i've had to do much of anything with a JFrame. What i was referring to is that if you try to do "this.add()" multiple times you're only going to get the final pane on your JFrame. Easier IMO just to add a main JPanel to the frame then add stuff to that. The content pane is another option but i've never bothered.

if you try to do "this.add()" multiple times you're only going to get the final pane

That's a function of the layout manager. Change to FlowLayout for example and all the add()s will take.

Wow, time to think before posting. "this.add()" automatically adds to the content pane, you just have to be sure to set the layout of the frame. Simple doing this.setLayout(new FlowLayout()) should be sufficient.

Please post the current version of the code.

With having your scales as radio buttons, you should not need any action listener for them. Your only action listener should be handling the convert buttons. Then you can either have two action listeners and a function they both call for the convert or have one action listener and just have to check to see what button was pressed. And like Norm said, cant help with the gui being all FUBAR unless you post the new updates to the code.

What happens when you compile and execute the new version?

Please post the current version of the code.

Try debugging the code by adding lots of println() statements that print messages as each method is executed so you can see where the execution of the code is happening. Start in the main() method and then in each method that needs to be called for the GUI to be displayed.

Your main function is written incorrectly. The brackets go on the String not args.

--- Update ---

More problems, you're not going to see anything because you never set your frame visibility to true. Next, you will only see one panel because you arent adding more than just panel1 to your frame.

Please post the current version of the code.

Are you saying that you have NOT changed the code since the first post on March 16?

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class TempConverter extends JFrame implements ActionListener
{
   int inScale=0,outScale=0;//stores scale of input and output temperature
   String p="";//To store action command
   ButtonGroup inputGroup,outputGroup;
   JRadioButton b1_panel1,b2_panel1,b3_panel1;//radio buttons for selecting input temperature
   JRadioButton  b1_panel2,b2_panel2,b3_panel2;//radio buttons for selecting output temperatures
   JButton b1_panel3,b2_panel3;//buttons for third panel
   JTextField t1,t2;//for inputing and outputing statements
   JPanel panel1,panel2,panel3;//panels for output and selcting scales
   JLabel l1,l2;//to inform about input and output scales
   public void frame()//to initialise frame
   {
      this.setSize(500,500);
      this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      this.setPreferredSize(this.getPreferredSize());
      this.setVisible(true);
   }
   public void panel1()//to initialise first panel
   {
      b1_panel1=new JRadioButton("Kelvin");
      b2_panel1=new JRadioButton("Fahrenheit");
      b3_panel1=new JRadioButton("Celsius");
      inputGroup=new ButtonGroup();
      inputGroup.add(b1_panel1);
      inputGroup.add(b2_panel1);
      inputGroup.add(b3_panel1);
      l1=new JLabel("INPUT SCALE");
      panel1=new JPanel();
      panel1.setLayout(new BoxLayout(panel1,BoxLayout.LINE_AXIS));
      panel1.add(l1);
      panel1.add(b1_panel1);
      panel1.add(b2_panel1);
      panel1.add(b3_panel1);
      panel1.setPreferredSize(panel1.getPreferredSize());
      panel1.setVisible(true);
   }
   public void panel2()//to initialse second panel   
   {
      b1_panel2=new JRadioButton("Kelvin");
      b2_panel2=new JRadioButton("Fahrenheit");
      b3_panel2=new JRadioButton("Celsius");
      outputGroup=new ButtonGroup();
      outputGroup.add(b1_panel2);
      outputGroup.add(b2_panel2);
      outputGroup.add(b3_panel2);
      l2=new JLabel("OUTPUT SCALE");
      panel2=new JPanel();
      panel2.setLayout(new BoxLayout(panel2,BoxLayout.PAGE_AXIS));
      panel2.add(l2);
      panel2.add(b1_panel2);
      panel2.add(b2_panel2);
      panel2.add(b3_panel2);
      panel2.setPreferredSize(panel2.getPreferredSize());
      panel2.setVisible(true);
   }
   public void panel3()//to initialise third panel   
   {   
      b1_panel3=new JButton("CONVERT");
      b2_panel3=new JButton("Back");
      panel3=new JPanel();
      panel3.setLayout(new BoxLayout(panel3,BoxLayout.PAGE_AXIS));
      t1=new JTextField("Enter input temperature");
      t2=new JTextField();
      panel3.add(t1);
      panel3.add(b1_panel3);
      panel3.add(t2);
      panel3.add(b2_panel3);
      panel3.setPreferredSize(panel3.getPreferredSize());
      panel3.setVisible(true);
   }
   public void start()//to add first panel to frame and set action commands
   {
      b1_panel1.addActionListener(this);
      b1_panel1.setActionCommand("11");//first digit stores panel bieng used and second stores which button is pressed
      b2_panel1.addActionListener(this);
      b2_panel1.setActionCommand("12");
      b3_panel1.addActionListener(this);
      b3_panel1.setActionCommand("13");
      b1_panel2.addActionListener(this);
      b1_panel2.setActionCommand("21");
      b2_panel2.addActionListener(this);
      b2_panel2.setActionCommand("22");
      b3_panel2.addActionListener(this);
      b3_panel2.setActionCommand("23");
      b1_panel3.addActionListener(this);
      b1_panel3.setActionCommand("31");
      b2_panel3.addActionListener(this);
      b2_panel3.setActionCommand("32");
      this.add(panel1);
    }
   public void actionPerformed(ActionEvent e)
   {
       p=e.getActionCommand();
       switch(p.charAt(0))
       {    
           case '1'://first panel is used
           this.removeAll();
           this.add(panel2);
           inScale=Integer.valueOf(p.charAt(1));//setting input scale
           break;
           case '2'://second panel is used
           this.removeAll();
           this.add(panel3);
           outScale=Integer.valueOf(p.charAt(1));//setting output scale
           break;
           case '3'://last panel is used
           switch(p.charAt(1))
           {
                case '1'://used pressed back button
                this.removeAll();
                this.add(panel1);
                break;
                case '2'://user pressed convert button
                Double i=Double.parseDouble(t1.getText());
                Double r=calculate(i);//converting temperture
                t2.setText(Double.toString(r));break;
           }   
       }
   }
   public Double calculate(Double i)//to calculate output temperature
   {
           Double r=0.0;
           switch(this.inScale)
           {
                case 1://input scale=kelvin
                switch(this.outScale)
                {
                    case 1://output scale=kelvin
                    r=i;break;
                    case 2://output scale=farenhiet
                    r=9/5*(i-273.15)+32;break;
                    case 3://output scale=celcius
                    r=i-273.15;break;
                }
                break;
                case 2://input scale=farenhiet
                switch(this.outScale)
                {
                    case 1://output scale=kelvin
                    r=(5/9*(i-32)+273.15);;break;
                    case 2://output scale=farenhiet
                    r=i;break;
                    case 3://output scale=celcieus
                    r=5/9*(i-32);break;
                }
                break;
                case 3://input scale=celcius
                switch(this.outScale)
                {
                    case 1://output scale=kelvin
                    r=i+273.15;break;
                    case 2://output scale=farenhiet
                    r=(9/5*i)+32;break;
                    case 3://output scale=celcieus
                    r=i;break;
                }
                break;
           }
           return(r);   
   }
}
class test
{
 public static void main(String args[])throws IOException
 {
TempConverter q=new TempConverter();
   q.setTitle("Temperature Converter");
   q.panel1();
   q.panel2();
   q.panel3();
   q.start();
 }
}

The above code has a compiler error that needs to be fixed.

You need to read the tutorial on how to build a Swing GUI:
http://docs.oracle.com/javase/tutori...ing/index.html