Jack Davis Jack Davis - 27 days ago 13
Java Question

Array that Holds JButton Objects

Ok, so I'm attempting to do an exercise from a book I'm using to learn Java. Here is the code that I have so far:

import javax.swing.*;
import java.awt.GridLayout;
import java.awt.BorderLayout;
public class Calculator {
//Declaration of all calculator's components.
JPanel windowContent;
JTextField displayField;
JButton button0;
JButton button1;
JButton button2;
JButton button3;
JButton button4;
JButton button5;
JButton button6;
JButton button7;
JButton button8;
JButton button9;
JButton buttonPoint;
JButton buttonAdd;
JButton buttonEqual;
JPanel pl;

//Constructor creates the components in memory and adds the to the frame using combination of Borderlayout.
Calculator() {
windowContent= new JPanel();

// Set the layout manager for this panel
BorderLayout bl = new BorderLayout();
windowContent.setLayout(bl);

//Create the display field and place it in the North area of the window
displayField = new JTextField(30);
windowContent.add("North",displayField);

//Create button field and place it in the North area of the window
button0=new JButton("0");
button1=new JButton("1");
button2=new JButton("2");
button3=new JButton("3");
button4=new JButton("4");
button5=new JButton("5");
button6=new JButton("6");
button7=new JButton("7");
button8=new JButton("8");
button9=new JButton("9");
buttonAdd=new JButton("+");
buttonPoint = new JButton(".");
buttonEqual=new JButton("=");

//Create the panel with the GridLayout that will contain 12 buttons - 10 numeric ones, and button with the points
//and the equal sign.
pl = new JPanel ();
GridLayout gl =new GridLayout(4,3);
pl.setLayout(gl);
//Add window controls to the panel pl.
pl.add(button1);
pl.add(button2);
pl.add(button3);
pl.add(button4);
pl.add(button5);
pl.add(button6);
pl.add(button7);
pl.add(button8);
pl.add(button9);
pl.add(buttonAdd);
pl.add(buttonPoint);
pl.add(buttonEqual);

//Add the panel pl to the center area of the window
windowContent.add("Center",pl);
//Create the frame and set its content pane
JFrame frame = new JFrame("Calculator");
frame.setContentPane(windowContent);
//set the size of the window to be big enough to accomodate all controls.
frame.pack();
//Finnaly, display the window
frame.setVisible(true);
}

public static void main(String[] args) {
Calculator calc = new Calculator();
}
}


Here is the exercise in exact wording:


Modify the class Calculator.java to keep all numeric buttons in the 10-element array declared as follows:

Buttons[] numButtons= new Buttons[10];


Replace 10 lines that start from

button0=new JButton("0");


with a loop that creates the buttons and store them in this array.


Ok, so I tried declaring the array with the
Buttons[] numbuttons line
, but that just gave me the error:


Multiple markers at this line

-Buttons can not be resolved to a type

-Buttons can not be resolved to a type


I instead tried this:

JButton[] buttons = new JButton[10]


And then added each button to the array like this:

buttons[0] = "button0";


Doing this didn't give me an error when I declared the array, but when I wrote the
buttons[0]
line, I got this error:


Syntax error on token "buttons",delete this token


So, I need help figuring out how to do this. Also, the book can be found here: http://myflex.org/books/java4kids/JavaKid811.pdf and the practice is on page 73.
I apologize if I'm listing to much information. It's just because I'm very new to Java and I'm not sure what is necessary. Help is appreciated. Thanks.

Answer Source

What you are doing is trying to set the array space to a string when you need a JButton.

You should be doing this

buttons[0] = new JButton("0");

instead of

buttons[0] = "button0";

EDIT:

I just did this

import javax.swing.*;

public class test {

    public static void main(String[] args) {
        JButton[] buttons = new JButton[10];

        buttons[0] = new JButton("0");

        System.out.println(buttons[0].getText());
    }

}

and got

0 

for an output so your error isn't in that line.

EDIT: Code

Calculator.java

import javax.swing.*;
import java.awt.GridLayout;
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class Calculator {
    //Declaration of all calculator's components.
    JPanel windowContent;
    JTextField displayField;
    JButton buttons[];
    JButton buttonPoint;
    JButton buttonAdd;
    JButton buttonEqual;
    JPanel pl;

    //Constructor creates the components in memory and adds the to the frame using combination of Borderlayout.
    Calculator() {
        windowContent= new JPanel();
        buttons = new JButton[10];

    // Set the layout manager for this panel
        BorderLayout bl = new BorderLayout();
        windowContent.setLayout(bl);

    //Create the display field and place it in the North area of the window
        displayField = new JTextField(30);
        windowContent.add("North",displayField);

    //Create button field and place it in the North area of the window
        for(int i = 0; i < 10; i++) {
            buttons[i] = new JButton(String.valueOf(i));
        }

        buttonAdd=new JButton("+");
        buttonPoint = new JButton(".");
        buttonEqual=new JButton("=");

    //Create the panel with the GridLayout that will contain 12 buttons - 10 numeric ones, and button with the points
    //and the equal sign.
        pl = new JPanel ();
        GridLayout gl =new GridLayout(4,3);
        pl.setLayout(gl);
    //Add window controls to the panel pl.

        for(int i = 0; i < 10; i++) {
            pl.add(buttons[i]);
        }
        pl.add(buttonAdd);
        pl.add(buttonPoint);
        pl.add(buttonEqual);

    //Add the panel pl to the center area of the window
        windowContent.add("Center",pl);
    //Create the frame and set its content pane
        JFrame frame = new JFrame("Calculator");
        frame.setContentPane(windowContent);
    //set the size of the window to be big enough to accomodate all controls.
        frame.pack();
    //Finnaly, display the window
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        Calculator calc = new Calculator();
    }
}