How to make a Calculator in java

In this tutorials will teach how to make a calculator in java step by step. How to create the calculator in java swing application in best coding practice.

First Step

Declare the variables

String CalTotal;
int num1;
int num2;
String option;
int result;

You have to paste the below Codes 1 to 0 buttons

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         

        CalTotal = txtTotal.getText();
        txtTotal.setText(CalTotal + "1"); 
    }                                        

    private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    
          CalTotal = txtTotal.getText();
        txtTotal.setText(CalTotal + "2");
    }                                        

    private void jButton3ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        
          CalTotal = txtTotal.getText();
        txtTotal.setText(CalTotal + "3");
    }                                        

    private void jButton4ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
          CalTotal = txtTotal.getText();
        txtTotal.setText(CalTotal + "4");
    }                                        

    private void jButton5ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
          CalTotal = txtTotal.getText();
        txtTotal.setText(CalTotal + "5");
    }                                        

    private void jButton6ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
          CalTotal = txtTotal.getText();
        txtTotal.setText(CalTotal + "6");
    }                                        

    private void jButton7ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
          CalTotal = txtTotal.getText();
        txtTotal.setText(CalTotal + "7");
    }                                        

    private void jButton8ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
          CalTotal = txtTotal.getText();
        txtTotal.setText(CalTotal + "8");
    }                                        

    private void jButton9ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
          CalTotal = txtTotal.getText();
        txtTotal.setText(CalTotal + "9");
    }                                        

    private void jButton10ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
          CalTotal = txtTotal.getText();
        txtTotal.setText(CalTotal + "0");
    }

Paste the following codes to **+,-,*,/ button**

    private void jButton11ActionPerformed(java.awt.event.ActionEvent evt) {                                          
 
        option = "+";
        num1 = Integer.parseInt(txtTotal.getText());
        
        txtTotal.setText("");
        
    }                                         

    private void jButton12ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
         option = "-";
        num1 = Integer.parseInt(txtTotal.getText());
        
        txtTotal.setText("");
        
    }                                         

    private void jButton13ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
           option = "*";
        num1 = Integer.parseInt(txtTotal.getText());
        
        txtTotal.setText("");
        
    }                                         

    private void jButton14ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
           option = "/";
        num1 = Integer.parseInt(txtTotal.getText());
        
        txtTotal.setText("");
        
    }

Paste the following codes inside the = Button

    private void jButton15ActionPerformed(java.awt.event.ActionEvent evt) {                                          
 
        num2 =  Integer.parseInt(txtTotal.getText());
        
        if(option.equals("+"))
            result = num1 + num2;
        
         if(option.equals("-"))
            result = num1 - num2;
         
         if(option.equals("*"))
            result = num1 * num2;
        
          if(option.equals("/"))
            result = num1 / num2;
          
          txtTotal.setText(result + ""); 
    }

Paste the following codes inside the Clear Button

 private void jButton16ActionPerformed(java.awt.event.ActionEvent evt) {                                          
     
        txtTotal.setText("");
        result = (0);
        num1 = (0);
        num2 = (0);
        
    }