i need calculator buttons to be able to work.

Question

hi.

i'm making a calculator and need to get my buttons to work but i don't know what to do.

i have 2 ways of inserting numbers. 1) physically write the number in the field 2) push a button and the corresponding number should appear in the field.

i don't need the +-*/ and only 1 input is needed. when = is clicked my formula (number -1 *1.20 +2.80) is executed.

i've got everything else to work. i can type in a number and get an answer but i can't figure out how to get the buttons to do their job.

any help would be appreciated.

thanks

Answer 1

Your "formula", e.g. 1*1.20+2.80 is called an expression. It's most likely a String that you input somehow.

The "classic" way to do this is to parse the String into tokens, which in your case will be either numbers or operators. Then an expression evaluator chews on the stream of tokens and comes up with a result you can display.

This is a fair bit of work. Other people have already done it, fortunately. One example I found by Googling for "java expression evaluator" is this: http://lts.online.fr/dev/java/math.evaluator/

It does a lot more than you need. You can either use it as is or fiddle with it first.

---

Update: Getting number buttons to work.

String fieldContents = "";

JTextField field = new JTextField;

ActionListener acLi = new ActionListener() {
  public void actionPerformed(ActionEvent ae) {
    JButton btn = (JButton) ae.getSource();
    fieldContents += btn.getText();
    field.setText(fieldContents);
  }
};

JButton button0 = new JButton("0");
button0.addActionListener(acLi);
...
JButton button9 = new JButton("9");
button9.addActionListener(acLi);

That should mostly do it. Enjoy!

Answer 2

thanks for the help.

i finally figured out a way how to do it, all i did was add a set and get text