How to divide two ints and return a double in Java

Question

I'm new to Android and I'm having trouble with a maths app I am creating.

The basic premise is to present the user with 2 numbers between 0 and 20 (questionTextView) then show the user a grid containing 3 incorrect answers and 1 correct answer. The user then clicks on the correct answer.

The issue I'm having is that the correct answer is not displaying to 2 decimal points.

E.g. Question: 4 / 7

Answer 1: 12.59

Answer 2: 15.99

Answer 3: 9.93

Answer 4: 0 (Should be 0.57)

I don't understand why the correct answer is not displaying properly as I have cast both ints to doubles and included decimal formatting.

I've tried Math.round(), but I couldn't get this to work - perhaps due to the way I have generated the questions within a for loop????

The incorrect answers display properly.

Any assistance would be greatly appreciated.

Here is my code:

private static DecimalFormat df2 = new DecimalFormat("#.##");

public void generateQuestion(){

    //Create 2 random numbers between 0 and 20.
    Random rand = new Random();

    int a = rand.nextInt(21);
    int b = rand.nextInt(21);

    if (a==b){
        b = rand.nextInt(21);
    }

    questionTextView.setText(Integer.toString(a) + " / " + Integer.toString(b));

/*Create a random number between 0 and 3 to determine the grid square of 
the correct answer */
    locationOfCorrectAnswer = rand.nextInt(4);

    //Calculate the correct answer.
    double correctAnswer = (int)(((double)a/(double)b));

  //Generate an incorrect answer in case the correct answer is 
   randomly generated.
   double inCorrectAnswer;

    /*Loop through each square and assign either the correct answer or
    a randomly generated number. */
    for (int i=0; i<4; i++){
        if (i == locationOfCorrectAnswer){ 
            answers.add(df2.format(correctAnswer).toString());
        } else {
            inCorrectAnswer = 0.05 + rand.nextDouble() *20.0;

            while (inCorrectAnswer == correctAnswer){
                inCorrectAnswer = 0.05 + rand.nextDouble() *20.0;
            }
            answers.add(df2.format(inCorrectAnswer).toString());
        }
    }

    //Assign an answer to each of the buttons.
    button0.setText((answers.get(0)));
    button1.setText((answers.get(1)));
    button2.setText((answers.get(2)));
    button3.setText((answers.get(3)));

Answer 1

Choose one of:

double correctAnswer = (double)a/b;

or

double correctAnswer = a/(double)b;

or

double correctAnswer = (double)a/(double)b;

Answer 2

(((double)a/(double)b)) This will give you = 0.57 and then this (int) this will convert 0.57 to 0 here (int)(((double)a/(double)b)); because integer can only hold whole numbers hence decimal values will be truncated.

use this to keep decimal values

double correctAnswer = (((double)a/(double)b));

Update : To achieve the decimal result, only one operand need to be cast as double and the optimizations for second parameter will be done by compiler.

Update Credits : @stackoverflowuser2010 and @cricket_007.

double correctAnswer = (double)a/b; 

or

This can also be done without explicit casting with Type Conversion or Type Casting which is done by the compiler.

Example Credits : @Andreas

double correctAnswer = a;  // a , will automatically converted to double 
correctAnswer /= b;

Answer 3

You need to remove the cast to int before the division:

This line:

double correctAnswer = (int)(((double)a/(double)b));

Should look like this:

double correctAnswer = (((double)a/(double)b));