Calling a Method at run time - Java Discussion Boards

Re: User defined Method

MallardsReach24-Mar-20 7:39

MallardsReach

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

Re: User defined Method

Richard MacCutchan24-Mar-20 7:44

Richard MacCutchan

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.

Re: User defined Method

MallardsReach24-Mar-20 8:29

MallardsReach

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

Re: User defined Method

Richard MacCutchan24-Mar-20 10:16

Richard MacCutchan

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 ...

Re: User defined Method

MallardsReach24-Mar-20 22:17

MallardsReach

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

MallardsReach

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

Richard MacCutchan

23-Mar-20 0:54

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

Calling a Method at run time

MallardsReach21-Mar-20 22:32

MallardsReach

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");
		}

Re: Calling a Method at run time

Richard MacCutchan21-Mar-20 23:29

Richard MacCutchan

21-Mar-20 23:29

Where is current initialised? Also, it would be better to put the text of your questions and answers in some sort of List, and pass the current variable to the set method. All set then needs to do is select the values of question and answers based on the List index.

Re: Calling a Method at run time

MallardsReach22-Mar-20 0:38

MallardsReach

22-Mar-20 0:38

Hi Richard,
Thanks for taking the time to look and answer.
Here is the start of the code. Once I get it to work I will then read up on list. Just wanted to solve why its not working.When running the example in cmd does.

Java

public PracticeTest() {
    initComponents();
}

/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")


 int count=0,current=0;

/**
 *
 * @param s
 */


   set();  //set() on its own gives error, (invalid method declaration; return type required)
 {
   counter = 0
   set()  //set() like this no errors, build successful but doesn't show
 }

Re: Calling a Method at run time

Richard MacCutchan22-Mar-20 0:48

Richard MacCutchan

22-Mar-20 0:48

The last five lines of that do not make any sense.

The first line is (or should be) a method declaration (but it is not), hence the error message. A call to a method cannot exist at class level, it must be inside an executable block.

The next four define a method that has no name, so can never be executed.

Re: Calling a Method at run time

MallardsReach22-Mar-20 1:08

MallardsReach

22-Mar-20 1:08

That's done it Smile | :)

Not sure about the first five lines as I'm using Netbeans and it puts those lines in.

But this is the that solved it.

Quote:
A call to a method cannot exist at class level, it must be inside an executable block.

So all I needed was,

Java

private void rbSetQuestionFocusGained(java.awt.event.FocusEvent evt) {
        set();
}

As rbSetQuestion is selected at the start, the set() method is executed.
Now to have a look at lists.

Re: Calling a Method at run time

Richard MacCutchan22-Mar-20 4:08

Richard MacCutchan

22-Mar-20 4:08

MallardsReach wrote:
Not sure about the first five lines as I'm using Netbeans

Which is a good reason to abandon Netbeans and use a simple editor*. That way you know that all the code is what you have written, rather than something the framework thinks you need. Once you have really mastered Java then go back to Netbeans, but until then it is only getting in your way. I speak from experience of trying to learn Visual C++ and MFC at the same time.

*notepad, notepad++, eclipse, or even Visual Studio Code, will all do the job. There are probably also many others that I have never looked at.

Re: Calling a Method at run time

MallardsReach22-Mar-20 6:00

MallardsReach

22-Mar-20 6:00

Once again Richard, Thanks for the advice.
I guess like most beginners I couldn't understand how writing code in a text editor and running it in cmd made a visual program. I did start with notepad ++ and compiled and run some programs but the result only showed itself in the cmd window, what use is that? then after looking around and gaining a little more understanding, I looked at examples where the code was written, compiled and run.
Lo and behold a window popped up with a button on it!
I think Netbeans makes you feel like you know but as this thread has pointed out, it's just an illusion.
So back to notepad ++ and back to a step at a time. Will also look at the other editors available.

Mouse Dragged Event

MallardsReach18-Mar-20 11:15

MallardsReach

18-Mar-20 11:15

I've looked at various articles and examples none of which are working for me.
I have a jPanel inside of which is a jlabel.
In the MouseDragged event I have the following code.

Java

int x=evt.getX();
int y=evt.getY();
jLabel3.setLocation(x, y);
jLabel3.repaint();

The Label moves but it flickers and sometimes show a copy of it self.
Any help in the right direction would be appreciated.

Re: Mouse Dragged Event

Richard MacCutchan18-Mar-20 21:47

Richard MacCutchan

18-Mar-20 21:47

The problem is that dragging produces many events so your code will be repeatedly moving the label a couple of points, and repainting it. You need to limit the number of repaints somehow. It's a long time since I wrote any GUI code in Java, so I am not sure exactly how this is best achieved. I expect Google will find some samples that help, or even some of the example code found in The Java™ Tutorials[^].

Re: Mouse Dragged Event

MallardsReach18-Mar-20 22:07

MallardsReach

18-Mar-20 22:07

Thanks Richard,
It seems like Java is more of a behind the scenes type of language and not really GUI orientated despite the best efforts of netbeans and the like.
I guess I'll revert to VB as that does it everything you need for a windows environment even though it is platform dependent.

Re: Mouse Dragged Event

Richard MacCutchan19-Mar-20 0:01

Richard MacCutchan

19-Mar-20 0:01

Not true. You would face exactly the same issue in VB, C# C++ etc.

Re: Mouse Dragged Event

Richard MacCutchan19-Mar-20 0:06

Richard MacCutchan

19-Mar-20 0:06

See How to Write a Mouse Listener (The Java™ Tutorials > Creating a GUI With JFC/Swing > Writing Event Listeners)[^]

Re: Mouse Dragged Event

MallardsReach19-Mar-20 0:32

MallardsReach

19-Mar-20 0:32

Thanks Richard
I seem to remember it being easier in vb but could be looking through rose coloured specs.
I looked at the links you suggested but to no avail mind they are 12yrs old now so maybe not surprising.
I will try to use another idea instead.
I was trying to get a question with three possible answers and the user had to drag the correct answer in place, so maybe I'll look at seeing if a jTextField can be dragged around.
If that fails three radio buttons and they can click the one they think is the right answer.
I will stick with Java

Best Practice?

MallardsReach15-Mar-20 9:41

MallardsReach

15-Mar-20 9:41

I have created a method

Java

void getSecond(int secondNum)

and in each of my radio buttons I have the following two pieces of code to return a number to the method
both work fine but just wondered which is better practice?

First

Java

getSecond(11);

Second

Java

getSecond(Integer.parseInt(times12.getName()));

Re: Best Practice?

Eddy Vluggen15-Mar-20 13:31

Eddy Vluggen

15-Mar-20 13:31

There is no "better"; and if you can't explain how the statements differ, then the answer is "11", or "42".

Bastard Programmer from Hell Suspicious | :suss:

If you can't read my code, try converting it here[^]
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.

Re: Best Practice?

MallardsReach15-Mar-20 21:34

MallardsReach

15-Mar-20 21:34

Thanks for the reply Eddy,

Glad to hear there is no 'Better' that's good to know.
Of course I can explain how they differ, both return a number to the method one returns the name of the radio button it refers to the other returns the number placed in the buttons event.
So I will use the one that returns the name of the button as it can eliminate the mistake of returning a number for a different button.
But as there is no 'Better' way, then I guess it's how ever the programmer feels on the day.

Netbeans

MallardsReach15-Mar-20 0:13

MallardsReach

15-Mar-20 0:13

Hi I am looking at Netbeans and have in a button control the following code;

Java

int firstNum, answerNum = 0;
      for (firstNum = 1; firstNum <= 12; firstNum ++)
          answerNum = firstNum * 2;
           displayTable.setText(firstNum + " x 2  = " + answerNum);

but in the textarea it only shows 13 x 2 = 24
does the for not work in netbeans? or does it have to be done differently.

Re: Netbeans

Peter_in_278015-Mar-20 0:24

Peter_in_2780

15-Mar-20 0:24

That's exactly what I'd expect.

When firstNum is 12, answerNum is set to 24.
Then the for is executed again, increments firstNum to 13, then the test fails, so it goes on to display what you see.

Cheers,
Peter

Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012

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