Java GUI Calculator

My JTextArea does not display and no errors or problems shows up. It’s a Java GUI Calculator.

Main class code:

    import javax.swing.JFrame;


    public class calulator_main{

        public static void main(String[] args) {
            // TODO Auto-generated method stub
            calulator_ui frame = new calulator_ui();
            frame.frame.setVisible(true);
        }

    }

Calculator code:

import java.awt.BorderLayout;
import java.awt.FlowLayout;        
import javax.swing.*;        
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class calulator_ui extends calulator_main {

    JFrame frame = new JFrame("cal");

    JPanel panel = new JPanel(new FlowLayout());
    JPanel screen = new JPanel(new BorderLayout());
    JTextArea text = new JTextArea(1,20);
    JButton button1 = new JButton("1");
    JButton button2 = new JButton("2");
    JButton button3 = new JButton("3");
    JButton button4 = new JButton("4");
    JButton button5 = new JButton("5");
    JButton button6 = new JButton("6");
    JButton button7 = new JButton("7");

    JButton button8 = new JButton("8");
    JButton button9 = new JButton("9");
    JButton button0 = new JButton("0");

    JButton add = new JButton("+");
    JButton subtract = new JButton("-");
    JButton mutliple = new JButton("*");
    JButton divide = new JButton("/");
    JButton equals = new JButton("=");

    JButton clear = new JButton("C");

    JLabel label = new JLabel();



    double numberone,numbertwo,result;


    int addc=0, subc=0,mutlic=0,divc=0;






    public calulator_ui() {
        ui();
        placeComponets();
        createListeners();



    }




    public void placeComponets(){

        screen.add(text, BorderLayout.NORTH);
        panel.add(button0);
        panel.add(button1);
        panel.add(button2);
        panel.add(button3);
        panel.add(button4);
        panel.add(button5);
        panel.add(button6);
        panel.add(button7);
        panel.add(button8);
        panel.add(button9);
        panel.add(add);
        panel.add(mutliple);
        panel.add(subtract);
        panel.add(divide);
        panel.add(clear);
        panel.add(equals);
        panel.add(label);
    }


    public void ui(){

        frame.setVisible(true); 
        frame.setSize(250,200);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(panel);

    }




    public void createListeners(){

        this.button0.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.button1.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.button2.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.button3.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.button4.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.button5.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.button6.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.button7.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.button8.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.button9.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.add.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.subtract.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.mutliple.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.divide.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });
        this.equals.addActionListener(
                new ActionListener(){
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        onCutClicked(ae);
                    }
                });



    }

    void onCutClicked(ActionEvent ae){

        Object source = ae.getSource();

        if(source==button0)
        {
            text.append("0");

        }   

        if(source==button1)
        {
            text.append("1");

        }   

        if(source==button2)
        {
            text.append("2");

        }   

        if(source==button3)
        {
            text.append("3");

        }   

        if(source==button4)
        {
            text.append("4");

        }   

        if(source==button5)
        {
            text.append("5");

        }   

        if(source==button6)
        {
            text.append("6");

        }   

        if(source==button7)
        {
            text.append("7");

        }   

        if(source==button8)
        {
            text.append("8");

        }   

        if(source==button9)
        {
            text.append("9");


        }

        if (source==add)
        {
            numberone=number_reader();
            text.setText("");
            addc=1;
            subc=0;
            mutlic=0;
            divc=0;
        }

        if (source==subtract)
        {
            numberone=number_reader();
            text.setText("");
            addc=0;
            subc=1;
            mutlic=0;
            divc=0;
        }

        if (source==mutliple)
        {
            numberone=number_reader();
            text.setText("");
            addc=0;
            subc=0;
            mutlic=1;
            divc=0;
        }

        if (source==divide)
        {
            numberone=number_reader();
            text.setText("");
            addc=0;
            subc=0;
            mutlic=0;
            divc=1;
        }



        if (source==equals)
        {
            numbertwo=number_reader();
            if (addc>0)
            {
                result=numberone+numbertwo;
                text.setText(Double.toString(result));
            }

            if (subc>0)
            {
                result=numberone-numbertwo;
                text.setText(Double.toString(result));
            }

            if (divc>0)
            {
                result=numberone/numbertwo;
                text.setText(Double.toString(result));
            }

            if (mutlic>0)
            {
                result=numberone*numbertwo;
                text.setText(Double.toString(result));
            }

        }
    }









    public double number_reader()

    {

        double returnnumber;
        String numberstring;
        numberstring=text.getText();
        returnnumber=Double.valueOf(numberstring);

        return returnnumber;


    }


}

Any suggestions on improvements to the code?

Answer

You’re adding your JTextArea, text, to your screen JPanel,

screen.add(text, BorderLayout.NORTH);

but you’re adding screen to nothing, and so it makes complete sense that the JTextArea won’t show. You should add the JTextArea to a container that somehow is either directly or indirectly added to your JFrame, else it’s not going to show. There’s no magic here — the GUI will only show what you add to it.

Note that since your JTextArea is written to be a single row, why not just use a JTextField instead? But regardless, the container hierarchy of this component must reach the top level window.

As an aside, read up on and learn about arrays and ArrayLists as you can use this and for loops to shorten your program considerably, making it much easier to read, understand and debug.

Please have a look at the code in this example to see what I mean. It will produce this GUI: