Result of String.Format() is ignored but why?

Question

So I wanted to round my double values into numbers that contain only 2 decimals but cant figure out how to do it. How can I change my code in order to get 2 values that are rounded for 2 decimals? Any help with this would be appreciated.

btnAdd.setOnClickListener(new View.OnClickListener() {

    public void onClick(View v) {
        num1 = Double.parseDouble(numBase.getText().toString());
        num2 = Double.parseDouble(numNikotin.getText().toString());
        sum = num1 / 20 * num2;
        String resultN = Double.toString(sum);
        String.format("%.2f", resultN);
        addResult.setText(resultN);
        sum = num1 - sum;
        String resultB = Double.toString(sum);
        String.format("%.2f", resultB);
        addResult2.setText(resultB);
    }
});

Second sentence of the [documentation for String](https://docs.oracle.com/javase/8/docs/api/java/lang/String.html): *Strings are constant; their values cannot be changed after they are created.* — OH GOD SPIDERS, Oct 16 '17 at 10:27
Possible duplicate of [Immutability of Strings in Java](https://stackoverflow.com/questions/1552301/immutability-of-strings-in-java) — Alessandro Da Rugna, Oct 16 '17 at 10:59

Jens · Answer 1 · 2017-10-16T11:34:56.250

4

String.format(...); returns a new String. You have to assign it to a variable:

resultN= String.format("%.2f", sum );

Also the parameter must be numeric.

See the javadoc for more details

edited Oct 16 '17 at 11:34

answered Oct 16 '17 at 10:19

Jens

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Thanks I will try to assign it. I will come back with more information about my progress in a minute hold on. – tegabyte Oct 16 '17 at 10:22
So I tried it like this, but it crashes the app when I try to run it. What do I do now? – tegabyte Oct 16 '17 at 11:28

score 0 · Answer 2 · answered Oct 16 '17 at 10:21

0

Please check the below post: round up to 2 decimal places in java?

double roundOff = Math.round(a * 100.0) / 100.0;

or

String roundOffTo2DecPlaces(float val)
{
    return String.format("%.2f", val);
}

answered Oct 16 '17 at 10:21

Amit

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score 0 · Answer 3 · answered Oct 16 '17 at 10:23

0

use this

String resultN = String.format("%.2f", sum);

why cast to string ????????

String resultN = Double.toString(sum);
String.format("%.2f", resultN);

answered Oct 16 '17 at 10:23

saman.firouzi

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Because I need it to calculate something. sum = num1 - sum; – tegabyte Oct 16 '17 at 11:28
you don't need cast to string. String resultN = String.format("%.2f", sum); is enough – saman.firouzi Oct 16 '17 at 12:06

Result of String.Format() is ignored but why?

3 Answers3