My calculator program only takes single digit in he textfield when a button is pressed

Question

My calculator program only takes single digit in the textfield when a button is pressed. How can I make it take multiple digits when buttons are pressed? It replaces the original number that I pressed with the new number.

This is my code:

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

class cal  implements ActionListener
{
JFrame frame;
JPanel grid,flow;
JButton one,two,three,four,five,six,seven,eight,nine,zero,plus,sub,mul,div,equal,clear;
JTextField text;
JLabel em,em1,em2;
int b,c;

public cal()
{
frame=new JFrame("Calculator");     //frame
frame.setVisible(true);
frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
frame.setSize(600,600);

flow=new JPanel();          //panel
grid=new JPanel(new GridLayout(5,4));

one=new JButton("1");           //button
one.addActionListener(this);
two=new JButton("2");           //button
two.addActionListener(this);
three=new JButton("3");         //button
three.addActionListener(this);
four=new JButton("4");          //button
four.addActionListener(this);
five=new JButton("5");          //button
five.addActionListener(this);
six=new JButton("6");           //button
six.addActionListener(this);
seven=new JButton("7");         //button
seven.addActionListener(this);
eight=new JButton("8");         //button
eight.addActionListener(this);
nine=new JButton("9");          //button
nine.addActionListener(this);
zero=new JButton("0");          //button
zero.addActionListener(this);
plus=new JButton("+");          //button
plus.addActionListener(this);
sub=new JButton("-");           //button
sub.addActionListener(this);
mul=new JButton("*");           //button
mul.addActionListener(this);
div=new JButton("/");           //button
div.addActionListener(this);
equal=new JButton("=");         //button
equal.addActionListener(this);
clear=new JButton("Clear");         //button
clear.addActionListener(this);

text=new JTextField();      //textfield

em=new JLabel("");          //empty label
em1=new JLabel("");
em2=new JLabel("");

grid.add(text);
grid.add(em);
grid.add(em1);
grid.add(em2);
grid.add(one);
grid.add(two);
grid.add(three);
grid.add(plus);
grid.add(four);
grid.add(five);
grid.add(six);
grid.add(sub);
grid.add(seven);
grid.add(eight);
grid.add(nine);
grid.add(mul);
grid.add(clear);
grid.add(zero);
grid.add(equal);
grid.add(div);

flow.add(grid);
frame.add(flow);
}

public void actionPerformed(ActionEvent a)
{
if(a.getSource()==one)
text.setText("1");

if(a.getSource()==two)
text.setText("2");

if(a.getSource()==three)
text.setText("3");

if(a.getSource()==four)
text.setText("4");

if(a.getSource()==five)
text.setText("5");

if(a.getSource()==six)
text.setText("6");

if(a.getSource()==seven)
text.setText("7");

if(a.getSource()==eight)
text.setText("8");

if(a.getSource()==nine)
text.setText("9");

if(a.getSource()==zero)
text.setText("0");

if(a.getSource()==plus)
{
b=Integer.parseInt(text.getText());
c=1;
text.setText("");
}

if(a.getSource()==sub)
{
b=Integer.parseInt(text.getText());
c=2;
text.setText("");
}

if(a.getSource()==mul)
{
b=Integer.parseInt(text.getText());
c=3;
text.setText("");
}

if(a.getSource()==div)
{
b=Integer.parseInt(text.getText());
c=4;
text.setText("");
}

if(a.getSource()==equal)
{
if(c==1)
{
int x=Integer.parseInt(text.getText());
int y=b+x;
text.setText(Integer.toString(y));
}

if(c==2)
{
int x=Integer.parseInt(text.getText());
int y=b-x;
text.setText(Integer.toString(y));
}

if(c==3)
{
int x=Integer.parseInt(text.getText());
int y=b*x;
text.setText(Integer.toString(y));
}

if(c==4)
{
int x=Integer.parseInt(text.getText());
int y=b/x;
text.setText(Integer.toString(y));
}
}

if(a.getSource()==clear)
{
text.setText("");
b=0;
}
}
public static void main(String[] args)
{
cal a =new cal();
}
}

Works fine with a single digit, but not with multiple digits.

Answer 1

For multiple digits you need to append the current text with existing one. Code sample below

    String valueText=text.getText();

    if (a.getSource() == one)
        valueText=valueText.concat("1");

    if (a.getSource() == two)
        valueText=valueText.concat("2");

    if (a.getSource() == three)
        valueText=valueText.concat("3");

    if (a.getSource() == four)
        valueText=valueText.concat("4");

    if (a.getSource() == five)
        valueText=valueText.concat("5");

    if (a.getSource() == six)
        valueText=valueText.concat("6");

    if (a.getSource() == seven)
        valueText=valueText.concat("7");

    if (a.getSource() == eight)
        valueText=valueText.concat("8");

    if (a.getSource() == nine)
        valueText=valueText.concat("9");

    if (a.getSource() == zero)
        valueText=valueText.concat("0");

    text.setText(valueText);

Answer 2

The setText(...) method replaces the existing text with the new text.

Here is an example that shows how you can use the replaceSelection(...) method of the JTextField.

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

public class CalculatorPanel extends JPanel
{
    private JTextField display;

    public CalculatorPanel()
    {
        Action numberAction = new AbstractAction()
        {
            @Override
            public void actionPerformed(ActionEvent e)
            {
                display.setCaretPosition( display.getDocument().getLength() );
                display.replaceSelection(e.getActionCommand());
            }
        };

        setLayout( new BorderLayout() );

        display = new JTextField();
        display.setEditable( false );
        display.setHorizontalAlignment(JTextField.RIGHT);
        add(display, BorderLayout.NORTH);

        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout( new GridLayout(0, 5) );
        add(buttonPanel, BorderLayout.CENTER);

        for (int i = 0; i < 10; i++)
        {
            String text = String.valueOf(i);
            JButton button = new JButton( text );
            button.addActionListener( numberAction );
            button.setBorder( new LineBorder(Color.BLACK) );
            button.setPreferredSize( new Dimension(50, 50) );
            buttonPanel.add( button );

            InputMap inputMap = button.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
            inputMap.put(KeyStroke.getKeyStroke(text), text);
            inputMap.put(KeyStroke.getKeyStroke("NUMPAD" + text), text);
            button.getActionMap().put(text, numberAction);
        }
    }

    private static void createAndShowUI()
    {
//      UIManager.put("Button.margin", new Insets(10, 10, 10, 10) );

        JFrame frame = new JFrame("Calculator Panel");
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        frame.add( new CalculatorPanel() );
        frame.pack();
        frame.setLocationRelativeTo( null );
        frame.setVisible(true);
    }

    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowUI();
            }
        });
    }
}

The example also shows how to use a common ActionListener for all the buttons without using nested if/else statements.

Answer 3

if(a.getSource()==one)
    text.setText(text.getText()+"1");
if(a.getSource()==two)
    text.setText(text.getText()+"2");
......