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Round a doubleTag(s): String/Number


JDK1.1
import java.math.*;
public class TestRound11 {
  public static void main(String args[]){
    double d = 3.1537;
    BigDecimal bd = new BigDecimal(d);
    bd = bd.setScale(2,BigDecimal.ROUND_HALF_UP);
    // output is 3.15
    System.out.println(d + " : " + round(d, 2));
    // output is 3.154
    System.out.println(d + " : " + round(d, 3));
  }

  public static double round(double d, int decimalPlace){
    // see the Javadoc about why we use a String in the constructor
    // http://java.sun.com/j2se/1.5.0/docs/api/java/math/BigDecimal.html#BigDecimal(double)
    BigDecimal bd = new BigDecimal(Double.toString(d));
    bd = bd.setScale(decimalPlace,BigDecimal.ROUND_HALF_UP);
    return bd.doubleValue();
  }
}

JDK1.0.2

public class TestRound102 {
    public static void main(String args[]){
      double d = 3.1537;
      // output is 3.2
      System.out.println(d + " : " + round(d, 1));
      // output is 3.15
      System.out.println(d + " : " + round(d, 2));
      // output is 3.154
      System.out.println(d + " : " + round(d, 3));
      d= 9.155;
      // output is 9.2
      System.out.println(d + " : " + round(d, 1));
      // output is 9.16
      System.out.println(d + " : " + round(d, 2));
      // output is 3.155
      System.out.println(d + " : " + round(d, 3));
      d= 1234.156789;
      // output is 1234.2
      System.out.println(d + " : " + round(d, 1));
      // output is 1234.16
      System.out.println(d + " : " + round(d, 2));
      // output is 1234.157
      System.out.println(d + " : " + round(d, 3));
      // output is 1234.1568
      System.out.println(d + " : " + round(d, 4));
      d= 1.5;
      // output is 2
      System.out.println(d + " : " + round(d, 0));
    }

    // positive value only.
    public static double round(double value, int decimalPlace)
    {
      double power_of_ten = 1;
      // floating point arithmetic can be very tricky.
      // that's why I introduce a "fudge factor"
      double fudge_factor = 0.05;
      while (decimalPlace-- > 0) {
         power_of_ten *= 10.0d;
         fudge_factor /= 10.0d;
      }
      return Math.round((value + fudge_factor)* power_of_ten)  / power_of_ten;
    }
}

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