Is there a way to split JTextField with substrings into a double?

Question

Is there a way you can split up a JTextField using substrings and return it has a double. The problem is i will recieve an input from the user i.e 3+x+5*7+y or 5*y-x/4 in a JTextField and this will be a String. But in order to use it in my calculation, i believe it must be splitted or parsed into a variable which is double.

I believe you can take the index of the text, and check for everytime an -, +, *, /, x or y appears, and set the substrings together, but i can not figure out how this can be done.

It will avariable which is named double i and used in the following context:

public void solve(double y, double h, int j, double i){      
xArray = new double[j];
yArray = new double[j];
for(int dex = 0; dex < j; dex++){
    F1 = h*f(x,y,i);
    F2 = h*f(x+h/2,y+F1/2,i);
    F3 = h*f(x+h/2,y+F2/2,i);
    F4 = h*f(x+h,y+F3,i);

    y = y + 1.0/6.0*(F1+2*F2+2*F3+F4);

    xArray[dex] = x;
    yArray[dex] = y;

    x = x + h;
   }   
 } 
private double f(double x, double y, double i){
 return i; 
}

What have you tried for splitting the string? You could use a regex with split — phflack, Apr 27 '19 at 08:56
By any chance you could give me an example of how you think it can be done using regex? — Aagaard, Apr 27 '19 at 10:14
Possible duplicate of [How to evaluate a math expression given in string form?](https://stackoverflow.com/questions/3422673/how-to-evaluate-a-math-expression-given-in-string-form) — Samuel Philipp, Apr 27 '19 at 11:14

score 0 · Answer 1 · edited Apr 27 '19 at 20:20

I believe you can take the index of the text, and check for every time an -, +, *, /, x or y appears and set the substrings together, but I can not figure out how this can be done.

this can be done with KeyListener interface which it provides 3 methods that can help you keyPressed, keyReleased and keyTyped each one of them has it's own functionality (although them names checks them out but their time of execution varies, a lot.)

here is an example

public class MyListener implements KeyListener {

        @Override
        public void keyTyped(KeyEvent e) {
            //empty implemntation , we are not using it 
        }

        @Override
        public void keyPressed(KeyEvent e) {
            //here we are implementing what we want for the app
            //using the KeyEvent method getKeyChar() to get the key that activated the event.
            char c = e.getKeyChar();
            //let's check it out !
            System.out.println(c);
            //now we got it we can do what we want 
            if (c == '+'
                    || c == '-'
                    || c == '*'
                    || c == '/') {
                // the rest is your's to handle as your app needs
            }
        }

        @Override
        public void keyReleased(KeyEvent e) {
            //empty implemntation , we are not using it 
        }

    }

so to get the key that the users hit we get it from the KeyEvent object.

when coming to the component part we add it like this

JTextComponent jtc = //create it whether it's text field , area , etc...
MyListener ml = new MyListener();
jtc.addKeyListener(ml);

the rest depends on how you are going to use the text String and remember this answer's how to know what the users just typed (char by char) but as an approach it's very bad !! imagine that the users decides to remove a digit or to change the caret location ,how would you handle it ?? so as our friend @phflack said I would recommend using Regex or String.split something like this:-

String toSplit = "5-5*5+5";
        String regex = "(?=[-+*/()])";
        String[] splited = toSplit.split(regex);
        for (String s : splited) {
            System.out.print(s + ",");
        }

and the output of this

5,-5,*5,+5,

but this is hardly a Regex I just showed you a sample for more information about the Regex read this and for the KeyListener you can read about it here and I hope this solved your problem.

Is there a way to split JTextField with substrings into a double?

1 Answers1