SE450: Simulation: Random numbers [9/13] Previous pageContentsNext page

To get predictable numbers, use Random(long seed). If you use the seed every time, you get the same series of random numbers.

java.util.Random

file:random/Util.java [source] [doc-public] [doc-private]
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package random;
import java.util.Random;

public class Util {
  private Util() {}
  static private Random RANDOM = new Random();

  /** doubles that differ by less than EPSILON should be considered equals */
  static public final double EPSILON = 1e-9;
  static public boolean isEquals(double x, double y) {
    return Math.abs(x-y) <= EPSILON;
  }
  static public boolean isLessOrEquals(double x, double y) {
    return (x-y) <= EPSILON;
  }
  static public boolean isLess(double x, double y) {
    return (x-y) < -EPSILON;
  }

  static public void setRandomSeed(long seed) {
    RANDOM.setSeed(seed);
  }
  static public double nextRandom(double min, double max) {
    if (Util.isLess(max,min))
      throw new IllegalArgumentException(max + " is smaller than " + min);
    return min + ((RANDOM.nextDouble()) * (max - min));
  }
}

file:random/UtilTEST.java [source] [doc-public] [doc-private]
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package random;

import static org.junit.Assert.*;
import org.junit.Test;

public class UtilTEST {

  @Test
  public void testEquals() {
    assertTrue (Util.isEquals(0.3, 0.3+0.5*Util.EPSILON));
    assertFalse(Util.isEquals(0.3, 0.3+2.0*Util.EPSILON));
    assertFalse(Util.isLess(0.3, 0.3+0.5*Util.EPSILON));
    assertTrue (Util.isLess(0.3, 0.3+2.0*Util.EPSILON));
    assertTrue (Util.isLessOrEquals(0.3, 0.3+0.5*Util.EPSILON));
    assertTrue (Util.isLessOrEquals(0.3, 0.3+2.0*Util.EPSILON));

    assertTrue (Util.isEquals(0.3+0.5*Util.EPSILON, 0.3));
    assertFalse(Util.isEquals(0.3+2.0*Util.EPSILON, 0.3));
    assertFalse(Util.isLess(0.3+0.5*Util.EPSILON, 0.3));
    assertFalse(Util.isLess(0.3+2.0*Util.EPSILON, 0.3));
    assertTrue (Util.isLessOrEquals(0.3+0.5*Util.EPSILON, 0.3));
    assertFalse(Util.isLessOrEquals(0.3+2.0*Util.EPSILON, 0.3));
  }
  @Test
  public void testRandom() {
    for (int i=0; i<100; i++) {
      double x=Util.nextRandom(i,i*i);
      assertTrue (Util.isLessOrEquals(i,x));
      assertTrue (Util.isLessOrEquals(x,i*i));
    }
  }
}

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