Overview: 2.9.0

  • Random numbers are generated with Math.random()
  • Math.abs(int) returns the absolute value of an integer
  • These methods are defined in java.lang.Math
    • These are static methods which means they can be called without creating an object
      • Math.abs(-33) would work even though you didn’t create a Math object
      • Called using the class name and the dot operator
        • ClassName.methodName()
        • just methodName() if called from within the same class

Math.random

  • returns a number between 0.0 and 0.99

  • Use Math.random and cast to int to create a random integer

  • A random number between min and max is defined by the formula (int)(Math.random() * (max-min+1))+min
import java.lang.Math;

public class MyUtilityClass {
    /**
    Generates a random number between min and max
    @param min is the minimum integer value which can be returned
    @param max is the maximum integer value which can be returned
    @return a random int from min -> max
    */
    public static int randInt(int min, int max) {
        int range = max - min + 1;
        return (int)(Math.random() * range) + min;
    }
}

Other functions

  • Math.abs(int)
    • Returns the absolute value of an int input
    • int return type
    • Math.abs(double) also works
      • double return type
  • Math.pow(double, double)
    • Returns the first parameter raised to the power of the second power
    • double return type
  • Math.sqrt(double)
    • Returns the positive square root of the input
    • double return type
  • Math.random()
    • Returns a value within the range [0.0, 1.0)

These methods are on the quick reference sheet!

Summary: 2.9.2

  • Static Math methods can be called using Math.methodName()
  • Values from Math.random can be manipulated to produce a random int or double in a set range
    • (int)(Math.random() * (max-min+1))+min creates a random int from min to max
      • (int)(Math.random() * (10-5+1))+5 creates a random number between 5 and 10