Converting string into int to find a result in java android

how to convert some character like this +,-,/,*, from String into an int,
i try to find some result using int, but this character +,-,/,* make it error,
when i am trying to convert from String into int,

normally when you type int i = 12+12 it will display the result of 24,
but when i am trying to convert it from String to int, my app force close, any advice?, thank you

Easy approach should be using ScriptEngine Library -

Go to build.gradle(Module:app).
Add this dependency - implementation 'io.apisense:rhino-android:1.0'

Then To calculate value of any string, do this -

Use same code for all operation(+ - * \ %), just change the string value.

    String s = "12+12";
    ScriptEngine scriptEngine = new ScriptEngineManager().getEngineByName("rhino");
    try {
        Object result = scriptEngine.eval(s);
        System.out.println("Result: "+result); // Result(Output) is: 24
    } catch (ScriptException e) {
        e.printStackTrace();
    }

Example -
When user enters in EditText 12+12 take it into a String s = editText.getText().toString()

Call a method - String result = calculateResult(s);

The method is -

private String calculateResult(String s) {
        ScriptEngine scriptEngine = new ScriptEngineManager().getEngineByName("rhino");
        Object result = null;
        try {
            result = scriptEngine.eval(s);
        } catch (ScriptException e) {
            e.printStackTrace();
        }
        return result.toString();   // returns 24
    }

Instead of Integer.parseInt(getTextView); , you will have to first extract the numbers from the string obtained from the TextView and then convert them to integer separately and then do the arithmetic operation.

Do it as below.

equal.setOnClickListener(new View.OnClickListener() {
    @Override             
    public void onClick(View v) {
        String getTextView = textView.getText().toString();
        String[] numbers = getTextView.split("+");
        int value = Integer.parseInt(numbers[0]) + Integer.parseInt(numbers[1]);
        textView.setText(value);  
    }
}

UPDATE
Replace

String[] numbers = getTextView.split("+");

With

String[] numbers = getTextView.split("\\+");

to prevent the dangling metacharacter error.

Do it as follows:

// Split the string from textView on '+'. In order to specify optional space before/after '+', use \\s*
String[] nums = textView.getText().toString().split("\\s*\\+\\s*");

// Parse each number into an integer, add them and then set the result into textView
textView.setText(Integer.parseInt(nums[0]) + Integer.parseInt(nums[1]));