1.11 Math Class

1. Exam Points

• Methods of the Math class:
  • static int abs(int x) : returns the absolute value of an int value.
  • static double abs(double x) : returns the absolute value of a double value.
  • static double pow(double base, double exponent) : returns the value of the first parameter raised to the power of the second parameter.
  • static double sqrt(double x) : returns the nonnegative square root of a double value.
  • static double random() : returns a double value greater than or equal to 0.0 and less than 1.0 (0.0 ≤ x < 1.0).
• Generate double or int random values using the Math.random() method.

2. Knowledge Points

(1) Math Class

• The Math class is part of the java.lang package.
• Classes in the java.lang package are available by default.
• The Math class contains only class methods.
• Methods in the Math class:
  • static int abs(int x) : returns the absolute value of an int value.
  • static double abs(double x) : returns the absolute value of a double value.
  • static double pow(double base, double exponent) : returns the value of the first parameter raised to the power of the second parameter.
  • static double sqrt(double x) : returns the nonnegative square root of a double value.
  • static double random() : returns a double value greater than or equal to 0.0 and less than 1.0 (0.0 ≤ x < 1.0).
• Example:
  

     // 1. int Math.abs(int x) and double Math.abs(double x) (绝对值)
     int result1 = Math.abs(-10); // result1: 10
     double result2 = Math.abs(-20.3); //result2: 20.3
     
     // 2. double Math.pow(double x, double y) x^y (x的y次方)
     double result3 = Math.pow(3.0, 4.0); //result3: 3 to the power of 4
  
     // 3. double Math.sqrt(double x): get the square root of x
     double result4 = Math.sqrt(16.0); // result4: 4.0
  
     // 4. double Math.random() (生成随机数)
     // 0.0 <= x < 1.0, generate a double value between [0,1)
     double result5 = Math.random(); // 0.0 <= result5 < 1.0
  
     // generate a double value between [0,10)
     double result6 = Math.random() * 10; // 0.0 <= result6 < 10.0
  
     // generate an integer value between [0,10)
     int result7 = (int) (Math.random() * 10); // 0 <= result7 <= 9
  
     // generate an integer value between [1,10]
     int result8 = (int) (Math.random() * 10) + 1; // 1 <= result8 <= 10
  
     // generate an integer value between [m,n] (m <= x <= n)
     int m = 3;
     int n = 15;
     int result9 = (int) (Math.random() * (n - m + 1)) + m;
     
  

• The values returned from Math.random() can be manipulated using arithmetic and casting operators to produce a random int or double in a defined range based on specified criteria.
• Example:
  

3. Exercises

• Practice
• Solution