Defective code for dice, help please?

[byron]

I'm using NetBeans to create a dice program. As such, the entire code is automatically created, except for the following:

private void rollActionPerformed(java.awt.event.ActionEvent evt) {
Random dice = new Random();
int throw = dice.nextInt(6) + 1;
number.setText(throw);
}

(I also put "import java.util.Random;" at the top of the program, just below package declaration)

My program (which has a GUI, which is why I used NetBeans) consists of a JFrame, 2 JLabels (one is called "title" and is the title of the program ["Virtual Dice"], and the other is called "number", and is where I try to set the random number the program generated.) and a JButton (titled "roll") which makes the program

Anyways, NetBeans tells me the last two lines are bad. The second to last one says " ';' expected/not a statement/illegal start of expression" (I have replaced line breaks with a slash in the above.) The last line is bad because "illegal start of expression/illegal start of expression".

So what do I need to do it to fix this program?

Peace,
Byron

P.S., here is the entire source code:

/*
* virtualDice.java
*
* Created on February 16, 2008, 8:32 AM
*/

package virtualDice;

import java.util.Random;
/**
*
* @author Byron&Cheryl
*/
public class virtualDice extends javax.swing.JFrame {

/** Creates new form virtualDice */
public virtualDice() {
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.
*/
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {

title = new javax.swing.JLabel();
number = new javax.swing.JLabel();
roll = new javax.swing.JButton();

setDefaultCloseOperation(javax.swing.WindowConstan ts.EXIT_ON_CLOSE);

title.setFont(new java.awt.Font("Tahoma", 0, 24));
title.setText("Virtual Dice");
title.setHorizontalTextPosition(javax.swing.SwingC onstants.CENTER);

number.setFont(new java.awt.Font("Tahoma", 0, 36));
number.setText("0");

roll.setText("Roll!");
roll.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
rollActionPerformed(evt);
}
});

javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout .Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.G roupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(160, 160, 160)
.addComponent(number, javax.swing.GroupLayout.PREFERRED_SIZE, 59, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(layout.createSequentialGroup()
.addGap(145, 145, 145)
.addComponent(roll))
.addGroup(layout.createSequentialGroup()
.addGap(108, 108, 108)
.addComponent(title)))
.addContainerGap(116, Short.MAX_VALUE))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout .Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(6, 6, 6)
.addComponent(title)
.addPreferredGap(javax.swing.LayoutStyle.Component Placement.UNRELATED)
.addComponent(number, javax.swing.GroupLayout.PREFERRED_SIZE, 42, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.Component Placement.RELATED)
.addComponent(roll)
.addContainerGap(javax.swing.GroupLayout.DEFAULT_S IZE, Short.MAX_VALUE))
);

pack();
}// </editor-fold>

private void rollActionPerformed(java.awt.event.ActionEvent evt) {
Random dice = new Random();
int throw = dice.nextInt(6) + 1;
number.setText(throw);
}

/**
* @param args the command line arguments
*/
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new virtualDice().setVisible(true);
}
});
}

// Variables declaration - do not modify
private javax.swing.JLabel number;
private javax.swing.JButton roll;
private javax.swing.JLabel title;
// End of variables declaration

}

[kurtulas]

Hi Byron,

Im not 100% with this but im pretty sure you cannot use 'throw' as a declared variable as it is a key word in java.

Hope this helps.

Kurt

[byron]

Hi Byron,

Im not 100% with this but im pretty sure you cannot use 'throw' as a declared variable as it is a key word in java.

Hope this helps.

Kurt

Okay, I changed "throw" to "numb" (short for number), and then tried to compile it. NetBeans now says:

C:\Users\Byron&Cheryl\Documents\NetBeansProjects\V irtual Dice\src\virtualDice\virtualDice.java:84: setText(java.lang.String) in javax.swing.JLabel cannot be applied to (int)

Java is starting to give me a headache... :)

[Bluefox815]

setText(java.lang.String) tells you what the method needs to be given (a String object)
but you gave it an int.

private void rollActionPerformed(java.awt.event.ActionEvent evt) {
Random dice = new Random();
int throw = dice.nextInt(6) + 1;
number.setText(throw);
}

throw is an int and you tried to give throw (or numb) to setText()

Try this instead

private void rollActionPerformed(java.awt.event.ActionEvent evt) {
Random dice = new Random();
Integer numb = dice.nextInt(6) + 1;
number.setText(numb.toString());
}

numb is now an Integer and an Integer can be changed to a String with .toString()

Also, you should put

import java.awt.event.ActionEvent;

So you only have to write

private void rollActionPerformed(ActionEvent evt) {
}

And lastly, it probably wont know what number is because your variable declarations (fields) are at the bottom of the file, you should put them directly under your class declaration

// package and import statements

public class virtualDice extends javax.swing.JFrame {

// variable declarations

// all your other code

}

[byron]

Okay here is my new code:

/*
* virtualDice.java
*
* Created on February 16, 2008, 8:32 AM
*/

package virtualDice;

import java.util.Random;
/**
*
* @author Byron&Cheryl
*/
public class virtualDice extends javax.swing.JFrame {

// Variables declaration - do not modify
private javax.swing.JLabel number;
private javax.swing.JButton roll;
private javax.swing.JLabel title;
// End of variables declaration
/** Creates new form virtualDice */

public virtualDice() {
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.
*/
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {

title = new javax.swing.JLabel();
number = new javax.swing.JLabel();
roll = new javax.swing.JButton();

setDefaultCloseOperation(javax.swing.WindowConstan ts.EXIT_ON_CLOSE);

title.setFont(new java.awt.Font("Tahoma", 0, 24));
title.setText("Virtual Dice");
title.setHorizontalTextPosition(javax.swing.SwingC onstants.CENTER);

number.setFont(new java.awt.Font("Tahoma", 0, 36));
number.setText("0");

roll.setText("Roll!");
roll.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
rollActionPerformed(evt);
}
});

javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout .Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.G roupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(160, 160, 160)
.addComponent(number, javax.swing.GroupLayout.PREFERRED_SIZE, 59, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(layout.createSequentialGroup()
.addGap(145, 145, 145)
.addComponent(roll))
.addGroup(layout.createSequentialGroup()
.addGap(108, 108, 108)
.addComponent(title)))
.addContainerGap(116, Short.MAX_VALUE))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout .Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(6, 6, 6)
.addComponent(title)
.addPreferredGap(javax.swing.LayoutStyle.Component Placement.UNRELATED)
.addComponent(number, javax.swing.GroupLayout.PREFERRED_SIZE, 42, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.Component Placement.RELATED)
.addComponent(roll)
.addContainerGap(javax.swing.GroupLayout.DEFAULT_S IZE, Short.MAX_VALUE))
);

pack();
}// </editor-fold>

private void rollActionPerformed(java.awt.event.ActionEvent evt) {
Random dice = new Random();
int numb = dice.nextInt(6) + 1;
number.setText(numb.toString());
}

/**
* @param args the command line arguments
*/
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new virtualDice().setVisible(true);
}
});
}


}

Now NetBeans says:

C:\Users\Byron&Cheryl\Documents\NetBeansProjects\V irtual Dice\src\virtualDice\virtualDice.java:90: int cannot be dereferenced

to the line that says

number.setText(numb.toString());

What does dereferencing mean? I'm so confused!

[Bluefox815]

private void initComponents() {

title = new javax.swing.JLabel();
number = new javax.swing.JLabel();
roll = new javax.swing.JButton();

setDefaultCloseOperation(javax.swing.WindowConstan ts.EXIT_ON_CLOSE);

title.setFont(new java.awt.Font("Tahoma", 0, 24));
title.setText("Virtual Dice");
title.setHorizontalTextPosition(javax.swing.SwingC onstants.CENTER);

number.setFont(new java.awt.Font("Tahoma", 0, 36));
number.setText("0");

roll.setText("Roll!");
roll.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
rollActionPerformed(evt);
}
});

First of all, what is that parenthesis at the end? It shouldn't be there, neither should the semicolon, they will probably give you problems later. ALSO make sure you replace it with a bracket ( } ), you are one short.

EDIT: I'm sorry, that parenthesis and semi-colon are required, my apologies.

And for the dereferencing, you tried to use toString() on an int, and not on an Integer object. You see, int is a primitive data type, like boolean, or double, or byte.
Integer is a class file, like String, or JFrame, or virtualDice (btw, you should rename it to VirtualDice, class names are just supposed to start with a capital, you named everything else right).
Integer actually has a method called toString() for you to use, not the int data type. So you need to do this

private void rollActionPerformed(java.awt.event.ActionEvent evt) { 
Random dice = new Random();
Integer numb = new Integer(dice.nextInt(6) + 1);
number.setText(numb.toString());
}

That part should work perfectly :)

[byron]

Okay, I decided to give up on the above pregenerated code. I learned a little swing, and made a new code.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;

  public class diceGUI {
    public static void main(String[] args) {
	JFrame frame = new JFrame("Virtual Dice");
	frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	Box f = Box.createVerticalBox();

	
	Random generator = new Random(); //initiates the random generator
	
  	//titleLabel
	JLabel titleLabel = new JLabel("<html><big>Virtual Dice</big></html>");
	f.add(titleLabel);
	f.add(Box.createVerticalStrut(25));

  	//resultLabel
	JLabel resultLabel = new JLabel("Roll: --");
	f.add(resultLabel);
	f.add(Box.createVerticalStrut(25));
  	
	// rollButton
	JButton rollButton = new JButton("Roll!");
	rollButton.addActionListener(new ActionListener() {
		public void actionPerformed (ActionEvent event) {
			int diceThrow = generator.nextInt(6) + 1;  \\[b]javac says:  "local variable generator is accessed from within inner class.  Needs to be declared final."[/b]
			resultLabel.setText("Roll: " +diceThrow);  \\[b]javac says:  ""local variable resultLabel is accessed from within inner class.  Needs to be declared final."[/b]

		}
	});
	f.add(rollButton);

	frame.add(f, BorderLayout.CENTER);
	frame.setSize(150,200);
	frame.setVisible(true);
    }
  }

My problem,as I noted in the code as comments, is that I need to declare local variables as final. So a few questions arise:

What is a local variable?
what does it mean to declare a variable as final.
Why is it necessary to declare it as final?

Thanks, and peace to all!
Byron

[Bluefox815]

javac is saying that because your local variables resultLabel and generator, are trying to be used inside of your actionListener, this compiles and runs perfectly:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;

  public class DiceGUI {

    private static JLabel resultLabel;
    private static Random generator;

    public static void main(String[] args) {

	JFrame frame = new JFrame("Virtual Dice");
	frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	Box f = Box.createVerticalBox();

	
	generator = new Random(); //initiates the random generator
	
  	//titleLabel
	JLabel titleLabel = new JLabel("<html><big>Virtual Dice</big></html>");
	f.add(titleLabel);
	f.add(Box.createVerticalStrut(25));

  	//resultLabel
	resultLabel = new JLabel("Roll: --");
	f.add(resultLabel);
	f.add(Box.createVerticalStrut(25));
  	
	// rollButton
	JButton rollButton = new JButton("Roll!");
	rollButton.addActionListener(new ActionListener() {
		public void actionPerformed (ActionEvent event) {
			int diceThrow = generator.nextInt(6) + 1;
			resultLabel.setText("Roll: " +diceThrow);

		}
	});
	f.add(rollButton);

	frame.add(f, BorderLayout.CENTER);
	frame.setSize(150,200);
	frame.setVisible(true);
    }
  }

By the way, nice work on doing your own hardcode :) you only had one problem.

[byron]

javac is saying that because your local variables resultLabel and generator, are trying to be used inside of your actionListener, this compiles and runs perfectly:

Thanks, it does work. I'll go through the code a little later, and disect the differences and try to understand why.

By the way, nice work on doing your own hardcode :) you only had one problem.

Thanks. At least i know my studying paid off! One question, how can I center the button and JLabels? I can't figure out how to do that.

Well, anyways, thanks!!! I really appreciate it!!!

[King8654]

To center the JLabel, just need:

Example from code actually working on:

this.add(_aLabel, java.awt.BorderLayout.NORTH);
_aLabel.setHorizontalAlignment(JLabel.CENTER);

[Bluefox815]

if you invoke setAlignmentX(0.5f) for ALL components AND you use a JPanel with a BoxLayout, they will all be centered. I decided to rewrite the DiceGUI class so it uses this. Also, I rewrote the code to help you understand why the label had to be global (added comments explaining this)
NOTE: This WILL NOT compile! You cannot use the keyword "this" inside of a static method.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;

  public class DiceGUI implements ActionListener { // make DiceGUI an ActionListener object (DiceGUI now needs to have the method actionPerformed(ActionEvent)

    private static JLabel resultLabel;
    private static Random generator;

    // You see, actionPerformed is a separate method, and initializing resultLabel in main means this
    // method cannot see the variable because it is destroyed as soon as main ends

    public void actionPerformed (ActionEvent event) {
	int diceThrow = generator.nextInt(6) + 1;
	resultLabel.setText("Roll: " +diceThrow);
    }

    public static void main(String[] args) {

	JFrame frame = new JFrame("Virtual Dice");
	frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	JPanel f = new JPanel();
	f.setLayout(new BoxLayout(f, BoxLayout.Y_AXIS)); // BoxLayout.Y_AXIS makes the components go top to bottom

	
	generator = new Random(); //initiates the random generator
	
  	//titleLabel
	JLabel titleLabel = new JLabel("<html><big>Virtual Dice</big></html>");
	titleLabel.setAlignmentX(0.5f);
	f.add(titleLabel);
	f.add(Box.createVerticalStrut(25));

  	//resultLabel
	resultLabel = new JLabel("Roll: --");
	resultLabel.setAlignmentX(0.5f);
	f.add(resultLabel);
	f.add(Box.createVerticalStrut(25));
  	
	// rollButton
	JButton rollButton = new JButton("Roll!");
	rollButton.setAlignmentX(0.5f);
	rollButton.addActionListener(this); // this (DiceGUI) implements ActionListener and is now an ActionListener object (this is were the keyword 'this' is used inside static method main(String[]))
	f.add(rollButton);

	frame.add(f, BorderLayout.CENTER);
	frame.setSize(150,200);
	frame.setVisible(true);
    }
  }

However, this WILL compile (I gave you the code with errors to make it easier to understand the important concepts).

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;

  public class DiceGUI implements ActionListener {

    private static JLabel resultLabel;
    private static Random generator;

    public void actionPerformed (ActionEvent event) {
	int diceThrow = generator.nextInt(6) + 1;
	resultLabel.setText("Roll: " +diceThrow);
    }

    public void createGUI() {

	JFrame frame = new JFrame("Virtual Dice");
	frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	JPanel f = new JPanel();
	f.setLayout(new BoxLayout(f, BoxLayout.Y_AXIS));
	
	generator = new Random(); //initiates the random generator
	
  	//titleLabel
	JLabel titleLabel = new JLabel("<html><big>Virtual Dice</big></html>");
	titleLabel.setAlignmentX(0.5f);
	f.add(titleLabel);
	f.add(Box.createVerticalStrut(25));

  	//resultLabel
	resultLabel = new JLabel("Roll: --");
	resultLabel.setAlignmentX(0.5f);
	f.add(resultLabel);
	f.add(Box.createVerticalStrut(25));
  	
	// rollButton
	JButton rollButton = new JButton("Roll!");
	rollButton.setAlignmentX(0.5f);
	rollButton.addActionListener(this);
	f.add(rollButton);

	frame.add(f, BorderLayout.CENTER);
	frame.setSize(150,200);
	frame.setVisible(true);
    }

    public static void main(String[] args) {
	SwingUtilities.invokeLater(new Runnable() {
		public void run() {
			new DiceGUI().createGUI();
		}
	});
    }

  }