How to put two input in two seperate textfield with using a button in Java?

Question

Im building a basic calculator using jswing and I have two textfield, one for input #1 and for input #2. The question is, how can I continue putting my input so that when I finished entering my first input it should go to the next textfield for my second input? And also theres seems to be an error when operating the arithmetic formulation, the output displays the wrong answer or the total of two inputs.

import java.awt.event.*;


class Kalkuleytor implements ActionListener
{
    JFrame f;
    JTextField t1, t2, t3;
    JLabel lbl1, lbl2, lbl3, lbl4;
    JButton one,two,three,four,five,six,seven,eight,nine,zero,add,mltply,sbtrct,dvd,equal;

    static double a=0,b=0,c=0,result=0;
    static int operator=0;

    Kalkuleytor()
    {
        f=new JFrame("Calculator");
        t1=new JTextField();
        t2=new JTextField();
        t3=new JTextField();
        lbl1=new JLabel("Number 1");
        lbl2=new JLabel("Number 2");
        lbl3=new JLabel("");
        lbl4=new JLabel("Total");
        one=new JButton("1");
        two=new JButton("2");
        three=new JButton("3");
        four=new JButton("4");
        five=new JButton("5");
        six=new JButton("6");
        seven=new JButton("7");
        eight=new JButton("8");
        nine=new JButton("9");
        zero=new JButton("0");
        dvd=new JButton("/");
        mltply=new JButton("*");
        sbtrct=new JButton("-");
        add=new JButton("+");
        equal=new JButton("=");

        //setBounds and add of buttons

        f.setLayout(null);
        f.setVisible(true);
        f.setSize(517,502);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setResizable(false);

        one.addActionListener(this);
    //ActionListener for all button
    }

    public void actionPerformed(ActionEvent e)
    {
        if(e.getSource()==one)
            t1.setText("1");

        if(e.getSource()==two)
            t1.setText("2");

        if(e.getSource()==three)
            t1.setText("3");

        if(e.getSource()==four)
            t1.setText("4");

        if(e.getSource()==five)
            t1.setText("5");

        if(e.getSource()==six)
            t1.setText("6");

        if(e.getSource()==seven)
            t1.setText("7");

        if(e.getSource()==eight)
            t1.setText("8");

        if(e.getSource()==nine)
            t1.setText("9");

        if(e.getSource()==zero)
            t1.setText("0");

        if(e.getSource()==add)
        {
            a=Double.parseDouble(t1.getText());
            operator=1;
            lbl3.setText("+");
        } 

        if(e.getSource()==sbtrct)
        {
            a=Double.parseDouble(t1.getText());
            operator=2;
            lbl3.setText("-");
        }

        if(e.getSource()==mltply)
        {
            a=Double.parseDouble(t1.getText());
            operator=3;
            lbl3.setText("*");
        }

        if(e.getSource()==dvd)
        {
            a=Double.parseDouble(t1.getText());
            operator=4;
            lbl3.setText("/");
        }

        if(e.getSource()==equal)
        {
            c=Double.parseDouble(t1.getText());

            switch(operator)
            {
                case 1: result=a+b;
                    break;

                case 2: result=a-b;
                    break;

                case 3: result=a*b;
                    break;

                case 4: result=a/b;
                    break;

                default: result=0;
            }

            t3.setText(""+result);
        }       
    }

    public static void main(String[]args)
    {
        new Kalkuleytor();
    }
} 

enter image description here

Answer 1

You have more than one issue in this code.

• When you enter a value greater than 9 (2 buttons before your operator button) only the last digit will remain.
• You have two textfields t1 and and t2. On button 0 to 9 you fill t1 but you never fill t2.
• on the buttons +-*/ you convert the text in t1 to a value in the variable a but never convert the text in t2 to variable b

Textfields are for displaying so you can better use a separate variable of type String to register the input from the buttons 0-9 and concatenate them. Fill t1 of t2 depending on a boolean

Add the variables

String input = "";
boolean firstInput = true;

if(e.getSource()==one)
   t1.setText("1");

will become

if(e.getSource()==one){
    input += "1";
    if (firstInput ) {
        t1.setText(input);
    } 
    else {
        t2.setText(input);
    }
}

On the operators change

if(e.getSource()==add) {
   a=Double.parseDouble(t1.getText());
   operator=1;
   lbl3.setText("+");
} 

if(e.getSource()==add) {
   a=Double.parseDouble(input);
   operator=1;
   lbl3.setText("+");
   firstInput = false;
   input = "";
} 

on the equal sign

        if(e.getSource()==equal)
        {
            c=Double.parseDouble(t1.getText());

            switch(operator)
            {
                case 1: result=a+b;
                    break;

                case 2: result=a-b;
                    break;

                case 3: result=a*b;
                    break;

                case 4: result=a/b;
                    break;

                default: result=0;
            }

            t3.setText(""+result);
        }       
    }

to

if(e.getSource()==equal) {
   b=Double.parseDouble(input);

   switch(operator)
   {
    ....
   }
   t3.setText(""+result);
   firstInput = false;
   input = "";
}

Answer 2

1. To give the focus to an input you may use requestFocusInWindow()

2. The wrong result may come from that you used the wrong variable, in the equal if, you read the text into c and use b in the computations :

   if (e.getSource() == equal) {
       b = Double.parseDouble(t1.getText());
       switch (operator) {
       //...
   

---

Also you may simplify your code, you can easily refactor it:

• use else if when you can, like to get the number from the button, it can be one case only, don't try all, same for operators

  if(e.getSource()==one)
      t1.setText("1");
  else if(e.getSource()==two)
      t1.setText("2");
  

• You may directly read the JButton text from it and use it, don't try all possibilities

  Object source = e.getSource();
  if (source instanceof JButton) {
      JButton btn = (JButton) source;
      String textStr = btn.getText();
      if (textStr.matches("\\d")) {
          t1.setText(textStr);
      } else {
          lbl3.setText(textStr);
          a = Double.parseDouble(t1.getText());
          operator = textStr;
      }
  }
  

• You may also directly use a String to store the operator, don't bother you to pass to an int

  if (e.getSource() == equal) {
      b = Double.parseDouble(t1.getText());
      switch (operator) {
          case "+":
              result = a + b;
              break;
          case "-":
              result = a - b;
              break;
          case "*":
              result = a * b;
              break;
          case "/":
              result = a / b;
              break;
          default:
              result = 0;
      }
      t3.setText("" + result);
  }
  

The full code is here

---

Using more specific features, like BiFunction you could do :

    Map<String, BiFunction<Double, Double, Double>>  operators = new HashMap<>() {{
        put("+", (d1, d2) -> d1 + d2);
        put("-", (d1, d2) -> d1 - d2);
        put("*", (d1, d2) -> d1 * d2);
        put("/", (d1, d2) -> d1 / d2);
    }};

And

        } else {     // For = button
            b = Double.parseDouble(t1.getText());
            result = operators.getOrDefault(operator, (d1, d2) -> 0.0).apply(a, b);
            t3.setText("" + result);
        }

Answer 3

You need to use requestFocusInWindow() after you click on any operator (+,-,*,/,etc).