drop decimal in java

Question

public class Main {

    public static void main(String[] args) {
        generateRandomNumber();

    }

    public static void generateRandomNumber(){

        double[] insideArray = new double[5];

        for(int i=0; i<insideArray.length; i++) {
            double value = (Math.random()+1)*10;
            insideArray[i] = value;
            String.format("%.2f", insideArray[i]);
        }
        System.out.println("Displaying random generated Array: " + Arrays.toString(insideArray));

    }

}

I am trying to generate 5 random numbers and store to an Array. And I would like to format decimals up to 2 numbers. I tried "String.format()" method but didn't work. Still I am getting double like: 10.xxxxxxxxxxx.

How can I format it such as ex: 10.xx ?

`String.format("%.2f", insideArray[i]);` - this returns a string which you do nothing with. You need to assign it to something. — Amongalen, Jul 06 '20 at 08:11
Not a duplicate, the method used for rounding is good. This is a discard-returned-value issue, not a rounding issue — jhamon, Jul 06 '20 at 08:16
Ok thanks for your attentions. I found the solution : Double.parseDouble() method worked for me. — Sher, Jul 06 '20 at 08:32
@jhamon then [this](https://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value) could be an appropriate duplicate — Lino, Jul 06 '20 at 08:47

score 2 · Answer 1 · answered Jul 06 '20 at 08:29

String.format(String, double); returns the formated String. It doesn't change the object you want to format.

In other words: insideArray[i] is still an unrounded double after calling String.format.

The easiest way to solve your issue would be to store the result of String.formatinside the array. But the result is a String and the array is a double array. Those type don't match.

You can either declare a second array to store the strings, or simply change the type of insideArray, as it seems you don't do anything further with its elements.

Solution A:

double[] insideArray = new double[5];
String[] myStringArray = new String[5];

for(int i=0; i<insideArray.length; i++) {
    double value = (Math.random()+1)*10;
    insideArray[i] = value;
    myStringArray[i] = String.format("%.2f", insideArray[i]);
}
System.out.println("Displaying random generated Array: " + Arrays.toString(myStringArray));

Solution B:

String[] insideArray = new String[5];

for(int i=0; i<insideArray.length; i++) {
    double value = (Math.random()+1)*10;
    insideArray[i] =String.format("%.2f", value);
}
System.out.println("Displaying random generated Array: " + Arrays.toString(insideArray));

score 0 · Answer 2 · answered Jul 06 '20 at 09:35

When you print a double varible it can't be always limit to 2 decimal digits. Either use BigDecimal or store it in the form of string.

 public static void generateRandomNumber(){
        String [] insideArray = new String[5];   // double array to string array    
            for(int i=0; i<insideArray.length; i++) {
                double value = (Math.random()+1)*10;               
                insideArray[i] = String.format("%.2f", value);  // store the converted number in the form of string.            
            }
            System.out.println("Displaying random generated Array: " + Arrays.toString(insideArray));    
        }

drop decimal in java

2 Answers2