Rounding results from different java calculations

Question

So I've got the following code which makes some calculations depending on user input and then shows the results in a textView.

public class DescentCalculator extends AppCompatActivity {

EditText num1, num2, num3;
TextView resu;
double startdecent;
double feetminute;

@Override
public void onCreate ( Bundle savedInstanceState ) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.descent);

    Toolbar mToolbar = (Toolbar) findViewById(R.id.mtoolbar);
    setSupportActionBar(mToolbar);

    Button add = (Button) findViewById(R.id.button11);
    num1 = (EditText) findViewById(R.id.altitude_fix);
    num2 = (EditText) findViewById(R.id.altitude_cruise);
    num3 = (EditText) findViewById(R.id.mach_speed);
    resu = (TextView) findViewById(R.id.answer);

    add.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick ( View v ) {
            // TODO Auto-generated method stub

            String altfix = num1.getText().toString();
            String altcruise = num2.getText().toString();
            String machspeed = num3.getText().toString();


            startdecent = (Double.parseDouble(altcruise) - Double.parseDouble(altfix)) / 100 / 3;

            feetminute = (3 * Double.parseDouble(machspeed) * 1000);

            resu.setText(Double.toString(startdecent) + Double.toString(feetminute));


        }

    });
}

For example, if the user enters 7000 for the altcruise, 6000 for altfix and 0.30 for machspeed the app calculates the answer as 3.33333333333335899.999999999 which is technically right. I'd like the app to round up the answer and display 3.3 in this case.

Possible duplicate of https://stackoverflow.com/questions/50532/how-do-i-format-a-number-in-java — Dawood ibn Kareem, May 28 '17 at 20:57
Do you have a preference for "round", "ceil", "floor" or just truncate the decimals ? — Simon, May 28 '17 at 21:00
And you said you tried `resu.setText(new DecimalFormat("#0.0").format(startdecent))` but did not work ? Why does it not give you what you want ? — Simon, May 28 '17 at 21:06
Which answer did you try? And it what way did it fail to work? — Dawood ibn Kareem, May 28 '17 at 21:06
@DawoodibnKareem I've tried 1st , 2nd and the 4th one. No errors in android studio but I get the same answer . — D. Popa, May 28 '17 at 21:08
So you used the `format` method of the `DecimalFormat` class to build a `String`, then passed it to the `setText` method of your `TextView`? And it didn't work? I'm finding that a bit hard to believe. Perhaps you can show us the code where you did that, so we can see what you did wrong. — Dawood ibn Kareem, May 28 '17 at 22:01

score 1 · Answer 1 · answered May 28 '17 at 21:33

Look at this answer: Round a double to 2 decimal places

This code snippet takes in a double and reads it into a BigDecimal and rounds it returning a double with n decimalplaces.

public static void main(String[] args){

    double myDouble = 3.2314112;

    System.out.print(round(n,1));

}

public static double round(double value, int places) {
    if (places < 0) throw new IllegalArgumentException();

    BigDecimal bd = new BigDecimal(value);
    bd = bd.setScale(places, RoundingMode.HALF_UP);
    return bd.doubleValue();
}

This returns 3.2

Rounding results from different java calculations

1 Answers1