Simple Java Calculator Program Using Java Applet

Java calculator application using java applet JAppet and Swing components. how to make Simple java calculator applet. Java program source code for simple calculator applet
Screenshot of Simple calculator applet in java
This post shows a sample Calculator Program using Java Applet. This program uses the JApplet Class and Swing components in the program. The full source code is given below. This is a java Applet program for a simple calculator with operations addition, subtraction, division and multiplication on floating point numbers. It also have the C (clear) button. This Java Calculator applet was created by myself for my practical lab experiment. I think this may be useful for beginners in java.



import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JApplet;
import javax.swing.*;

/*
<applet code="Calculator.class" width=240 height=330></applet>

*/
public class Calculator extends JApplet {

    int KeySize=60;
    String operator="";
    float FirstNum;
    float SecondNum;
    String PressedKey;
    boolean IsResultShown=false;
    public void init() {
        getContentPane().setLayout(new GridLayout(2, 1));
        JTextField lcd=new JTextField();
        lcd.setText("0");
        lcd.setSize(KeySize*4, 30);
        add(lcd);
        JPanel buttonPanel=new JPanel();
        buttonPanel.setSize(4*KeySize,5*KeySize);
        buttonPanel.setLayout(new GridLayout(5, 4));
        JButton btns[]=new JButton[21];
        String keytexts1[]={"C","/","*","-","+"};
        String keytexts2[]={"0",".","="};
        for(int i=1;i<=20;i++)
        {   
            btns[i]=new JButton();
            btns[i].setSize(KeySize, KeySize);
            btns[i].setFont(new Font("Arial", Font.BOLD, 16));
            buttonPanel.add(btns[i]);
            if(i<4)
                {
                btns[i].setText("");
                btns[i].setEnabled(false);
                }
            else if(i>4&&i%4!=0&&i<16)
                btns[i].setText(Integer.toString(i%4+3*((i/4)-1)));
            else if(i%4==0)
                btns[i].setText(keytexts1[(i/4)-1]);
            else
                btns[i].setText(keytexts2[(i%4)-1]);
            if(i>3)
            {
            btns[i].addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    PressedKey=((JButton)e.getSource()).getText();
                    if(PressedKey.equals("C"))
                        {
                        FirstNum=0;
                        SecondNum=0;
                        lcd.setText("0");
                        operator="";
                        }
                    else if(PressedKey.equals("/")||PressedKey.equals("*")||PressedKey.equals("-")||PressedKey.equals("+"))
                        {
                        operator=PressedKey;
                        FirstNum=Float.parseFloat(lcd.getText());
                        lcd.setText("0");
                        }
                    else if(PressedKey.equals("="))
                        {
                        IsResultShown=true;
                        SecondNum=Float.parseFloat(lcd.getText());
                        float result=0.0f;
                        if(operator.equals("+"))
                            result=FirstNum+SecondNum;
                        else if(operator.equals("-"))
                            result=FirstNum-SecondNum;
                        else if(operator.equals("*"))
                            result=FirstNum*SecondNum;
                        else if(operator.equals("/"))
                            result=FirstNum/SecondNum;
                        lcd.setText(Float.toString(result));
                        }
                    else if(PressedKey.equals("."))
                        {
                        if(IsResultShown)
                            {
                                lcd.setText("0");
                                IsResultShown=false;
                            }
                        if(lcd.getText().contains(".")==false)
                            lcd.setText(lcd.getText()+".");
                        }
                    else 
                        {
                        if(IsResultShown||lcd.getText().equals("0"))
                            {
                                lcd.setText("");
                                IsResultShown=false;
                            }
                        lcd.setText(lcd.getText()+PressedKey);
                        }
                }
            });
            }
        }
        add(buttonPanel);   
    }
}

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