Calculator in Swing Java

Question

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class calc implements ActionListener
{
    JFrame f;
    JPanel p;
    JTextField jt1,jt2,jt3;
    JButton j1,j2;
    static double a=0,b=0,result=0;
    static int operator=0;

  calc() 
  {
      f = new JFrame();
      p = new JPanel();
      jt1 = new JTextField(20);
      jt2 = new JTextField(20);
      j1 = new JButton("+");
      j2 = new JButton("-");
      jt3 = new JTextField();

      f.add(p);
      p.add(jt1);
      p.add(jt2);
      p.add(j1);
      p.add(j2);
      j1.addActionListener(this);
      j2.addActionListener(this);

      f.setVisible(true);
      f.pack();
      f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }
  public void actionPerformed(ActionEvent ae)
  {
      if(ae.getSource()=="+")
      {
          a=Double.parseDouble(jt1.getText());
          operator = 1;
          b=Double.parseDouble(jt2.getText());
          switch(operator)
          {
              case 1: result=(a+b);

          }

          jt3.setText(result);

      }
  }
  public static void main(String [] args)
  {
      calc obj = new calc();
  }
}

i'm making a calculator using java swing, the output of this code is:

calc.java:48 error: incompatible types: double cannot be converted to String 
     jt3.setText(result);

i think this is not a big error, well help me to get rid of this, i just want to sum didn't add more functions like multiply or minus or etc, i just want to run as small code first then i'll add more functions to it well help will be appreciated thanks.

Can you explain which part of the error is not clear to you? — takendarkk, Dec 11 '17 at 15:45
You're trying to set the text field to a double. Text fields take in a string value. Convert result to a string first then assign it. — benjiiiii, Dec 11 '17 at 15:46
Java has a class `Double` with a static method `toString` which needs a `double` as parametre: https://docs.oracle.com/javase/7/docs/api/java/lang/Double.html#toString(double) — AntonH, Dec 11 '17 at 15:46
Side note:`ae.getSource()=="+"` will not work, use "equals" for strings — , Dec 11 '17 at 15:48
See also this [calculator example](http://stackoverflow.com/a/7441804/418556). It uses `ScriptEngine` to evaluate the expression in the text field. — Andrew Thompson, Dec 11 '17 at 15:51

score 1 · Answer 1 · answered Dec 11 '17 at 15:47

1

Easy way is:

//jt3.setText(result);
jt3.setText("" + result);

This will force the compiler to create a String of the two values.

answered Dec 11 '17 at 15:47

camickr

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thanks it is running but it is not adding two numbers in 3rd textfield, what's problem in this code? – AbHi TheNua Dec 12 '17 at 06:04
@AbHiTheNua, so the answer to the original question has been given. Glad it helped. Don't forget to "accept" the answer so people know the problem has been solved. – camickr Dec 12 '17 at 15:37
`it is not adding two numbers` - is the code being executed. Did you add debug code to the if statement. Did you read the comments about not using "==" for string comparison. If you still have problems, after following all the advice given then post a proper [mcve] in another question. And don't forget to name your class properly. Class names should start with an upper case character. – camickr Dec 12 '17 at 15:39

score 1 · Answer 2 · answered Dec 11 '17 at 15:47

1

Use jt3.setText(String.valueOf(result));.
.setText() only accept String type.
You can see it in Class TextField.

answered Dec 11 '17 at 15:47

KL_

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score 1 · Answer 3 · answered Dec 11 '17 at 15:51

1

Class text can accept only string values.
where the result you provided as an argument is Double

You can use this to convert it as a string

string converted = Double.toString(result);

answered Dec 11 '17 at 15:51

Rahul

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If you find the answer you wanted, Press the tick mark on the side, or if you have further questions, comment. – Rahul Dec 11 '17 at 15:57

score 0 · Answer 4 · answered Dec 11 '17 at 15:53

This error is because JTextField is expecting a String to set the text to it, not a double, so, you need to either:

jt3.setText(String.valueOf(result));

Or

jt3.setText("" + result);

The first one will convert result to a String value, while the second one will concatenate an empty String to result, and return a String as well.

However one last suggestion I want you to take note of is, don't use single letter variables, make them more descriptive, for example:

JFrame f; //This should be JFrame frame;

The same for the JPanel and the rest of your variables, since in larger programs it could be hard to remember that f means a JFrame and not the conversion to Fahrenheit from Celsius or a formula like F = m * a, it may be confusing and really hard to debug / understand later on.

And also as has been said in the comments above, use .equals to compare String in Java, see How do I compare strings in Java? for more on this

Calculator in Swing Java

4 Answers4