Java Simple Calculator

java swing jbutton actionlistener calculator
Lahiru Kavinda picture Lahiru Kavinda · Jun 30, 2013 · Viewed 19.1k times · Source

I have made this calculator program in Java. This works well only when two numbers are calculated at one time. That means to get the sum of 1+2+3 you have to go this way : press 1 press + press 2 press = press + press 3 press =

and it calculates it as 6.

But I want to program this so that I can get the answer by: press 1 press + press 2 press + press 3 press =

but this gives the answer 5!!! How to code this so that it works like an ordinary calculator?

Here is my code:

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

public class cal1 extends JFrame {

double op1 = 0d, op2 = 0d;
double result = 0d;
char action;
boolean b = false;
boolean pressequal = false;

public cal1() {
    makeUI();
}

private void makeUI() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(400, 400);

    b0 = new JButton("0");
    b1 = new JButton("1");
    b2 = new JButton("2");
    b3 = new JButton("3");
    b4 = new JButton("4");
    b5 = new JButton("5");
    b6 = new JButton("6");
    b7 = new JButton("7");
    b8 = new JButton("8");
    b9 = new JButton("9");
    bDot = new JButton(".");
    bMul = new JButton("*");
    bDiv = new JButton("/");
    bPlus = new JButton("+");
    bMinus = new JButton("-");
    bEq = new JButton("=");

    t = new JTextField(12);
    t.setFont(new Font("Tahoma", Font.PLAIN, 24));
    t.setHorizontalAlignment(JTextField.RIGHT);

    numpad = new JPanel();
    display = new JPanel();

    numpad.add(b7);
    numpad.add(b8);
    numpad.add(b9);
    numpad.add(bMul);
    numpad.add(b4);
    numpad.add(b5);
    numpad.add(b6);
    numpad.add(bDiv);
    numpad.add(b1);
    numpad.add(b2);
    numpad.add(b3);
    numpad.add(bMinus);
    numpad.add(bDot);
    numpad.add(b0);
    numpad.add(bEq);
    numpad.add(bPlus);

    numpad.setLayout(new GridLayout(4, 5, 5, 4));

    display.add(t);
    add(display, BorderLayout.NORTH);
    add(numpad, BorderLayout.CENTER);

    t.addKeyListener(new KeyAdapter() {
        @Override
        public void keyTyped(KeyEvent e) {
            typeOnt(e);
        }
    });

    b0.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            b0pressed(e);
        }
    });

    b1.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            b1pressed(e);
        }
    });

    b2.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            b2pressed(e);
        }
    });

    b3.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            b3pressed(e);
        }
    });

    b4.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            b4pressed(e);
        }
    });

    b5.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            b5pressed(e);
        }
    });

    b6.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            b6pressed(e);
        }
    });

    b7.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            b7pressed(e);
        }
    });

    b8.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            b8pressed(e);
        }
    });

    b9.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            b9pressed(e);
        }
    });

    bDot.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            bDotpressed(e);
        }
    });

    bPlus.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            bPlusPressed(e);
        }
    });

    bMinus.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            bMinusPressed(e);
        }
    });

    bMul.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            bMulPressed(e);
        }
    });

    bDiv.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            bDivPressed(e);
        }
    });

    bEq.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            bEqpressed(e);
        }
    });

}

void typeOnt(KeyEvent e) {
    e.consume();
}

void b0pressed(ActionEvent e) {
    if (b) {
        t.setText(null);
        b = false;
        t.setText(t.getText() + "0");
    } else {
        t.setText(t.getText() + "0");
    }
}

void b1pressed(ActionEvent e) {
    if (b) {
        t.setText(null);
        b = false;
        t.setText(t.getText() + "1");
    } else {
        t.setText(t.getText() + "1");
    }
}

void b2pressed(ActionEvent e) {
    if (b) {
        t.setText(null);
        b = false;
        t.setText(t.getText() + "2");
    } else {
        t.setText(t.getText() + "2");
    }
}

void b3pressed(ActionEvent e) {
    if (b) {
        t.setText(null);
        b = false;
        t.setText(t.getText() + "3");
    } else {
        t.setText(t.getText() + "3");
    }
}

void b4pressed(ActionEvent e) {
    if (b) {
        t.setText(null);
        b = false;
        t.setText(t.getText() + "4");
    } else {
        t.setText(t.getText() + "4");
    }
}

void b5pressed(ActionEvent e) {
    if (b) {
        t.setText(null);
        b = false;
        t.setText(t.getText() + "5");
    } else {
        t.setText(t.getText() + "5");
    }
}

void b6pressed(ActionEvent e) {
    if (b) {
        t.setText(null);
        b = false;
        t.setText(t.getText() + "6");
    } else {
        t.setText(t.getText() + "6");
    }
}

void b7pressed(ActionEvent e) {
    if (b) {
        t.setText(null);
        b = false;
        t.setText(t.getText() + "7");
    } else {
        t.setText(t.getText() + "7");
    }
}

void b8pressed(ActionEvent e) {
    if (b) {
        t.setText(null);
        b = false;
        t.setText(t.getText() + "8");
    } else {
        t.setText(t.getText() + "8");
    }
}

void b9pressed(ActionEvent e) {
    if (b) {
        t.setText(null);
        b = false;
        t.setText(t.getText() + "9");
    } else {
        t.setText(t.getText() + "9");
    }
}

void bDotpressed(ActionEvent e) {
    if (!t.getText().contains(".")) {
        if (b) {
            t.setText(null);
            b = false;
            t.setText(t.getText() + "0.");
        } else if (t.getText().isEmpty()) {
            t.setText("0.");
        } else {
            t.setText(t.getText() + ".");
        }
    }
}

void bPlusPressed(ActionEvent e) {
    b = true;
    action = '+';
    op1 = Double.parseDouble(t.getText());

}

void bMinusPressed(ActionEvent e) {
    b = true;
    action = '-';
    op1 = Double.parseDouble(t.getText());
}

void bMulPressed(ActionEvent e) {
    b = true;
    action = '*';
    op1 = Double.parseDouble(t.getText());
}

void bDivPressed(ActionEvent e) {
    b = true;
    action = '/';
    op1 = Double.parseDouble(t.getText());
}

void bEqpressed(ActionEvent e) {
    op2 = Double.parseDouble(t.getText());
    doCal();
}

void doCal() {
    switch (action) {
        case '+': result = op1 + op2; break;
        case '-': result = op1 - op2; break;
        case '*': result = op1 * op2; break;
        case '/': result = op1 / op2; break;
    }      
    t.setText(String.valueOf(result));
}

public static void main(String[] args) {
    new cal1().setVisible(true);
}

JButton b0;
JButton b1;
JButton b2;
JButton b3;
JButton b4;
JButton b5;
JButton b6;
JButton b7;
JButton b8;
JButton b9;
JButton bDot;
JButton bPlus;
JButton bMinus;
JButton bMul;
JButton bDiv;
JButton bEq;
JPanel display;
JPanel numpad;
JTextField t;
}

Answer

nachokk picture nachokk · Jun 30, 2013

First in Java classes should be start with first letter UpperCase Java Code Conventions

Second instead of creating a method for each number

void bpressed(ActionEvent e, Integer number) {
    if (b) {
        t.setText(null);
        b = false;
        t.setText(t.getText() + number);
    } else {
        t.setText(t.getText() + number);
    }
}

Use declarative names for things, what is b? it is not intuitive, class name should be Calculator or something like this, code must be readable for humans.

Related to your question you can have a partialResult when some operation is in progress. For example:

you declare 

private double partialResult=0D;

and a method something like this 

private void calculatePartialResult(Integer numberSelected){
      //choose depends on action
      partialResult op= numberSelected;  (where op in + - * /)    
  }

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