A detailed introduction to the Java Random class (Java generates random numbers)

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One, the use of Random class

Random class function, generate a random number

1. The basic syntax of Random class to generate random numbers (int):

(1) int取值范围Any number generated

Random r = new Random();
int num = r.nextInt();

(2) 指定范围Any number generated

Random r = new Random();
int num = r.nextInt(n);
//参数 n 代表指定范围的数字[0,n)

2. Several commonly used random number generation

method	parameter	Random number value range	Return value type	Instance
nextBoolean()	no	true、false	boolean	1
nextDouble()	no	[0.0，1.0)	double	2
nextFloat()	no	[0.0，1.0)	float	3
nextInt ()	no	The value range of int	int	4
nextInt(int bound)	Have	The parameter represents the number of the specified range [0, bound)	int	5
nextLong()	no	long value range	long	6
nextBytes(byte[] bytes)	Have	Generate byte.length numbers into byte[]	void	7

Code example-1

//生成Boolean随机数
Random r = new Random();
boolean b = r.nextBoolean();
System.out.println("生成的Boolean随机数是:"+b);

Code example-2

//生成double随机数
Random r = new Random();
double d = r.nextDouble();
System.out.println("生成的Double随机数是:"+d);

Code example-3

//生成Float随机数
Random r = new Random();
double f = r.nextFloat();
System.out.println("生成的Float随机数是:"+f);

Code example-4

//生成int随机数
Random r = new Random();
int i = r.nextInt();
System.out.println("生成的Int随机数是:"+i);

Code example-5

//生成[0,5)int随机数
Random r = new Random();
int i = r.nextInt(5);
System.out.println("生成[0,5)的]Int随机数是:"+i);

Code example-6

//生成Long随机数
Random r = new Random();
long l = r.nextLong();
System.out.println("生成的Long随机数是:"+l);

Code example-7

//将随机数字放入数组中
Random r = new Random();
byte[] arr = new byte[5];
r.nextBytes(arr);
for (int i = 0; i < arr.length; i++) {
    
    
    System.out.print(arr[i]+",");
}

Second, a detailed introduction to the Random class

1. Generate a specified range of numbers

左闭右闭 [a,b]：r.nextInt(b-a+1)+a

Random r = new Random();
int a = 5;
int b = 10;
int res = r.nextInt(b-a+1)+a;
System.out.println(res);

左闭右开 [a,b)：r.nextInt(b-a)+a

Random r = new Random();
int a = 5;
int b = 10;
int res = r.nextInt(b-a)+a;
System.out.println(res);

左开右闭 (a,b]：r.nextInt(b-a)+a+1

Random r = new Random();
int a = 5;
int b = 10;
int res = r.nextInt(b-a)+a+1;
System.out.println(res);

左开右开 (a,b)：r.nextInt(b-a-1)+a+1

Random r = new Random();
int a = 5;
int b = 10;
int res = r.nextInt(b-a-1)+a+1;
System.out.println(res);

2. The difference between Random.nextInt() and Math.random()

(1) Source ¹

• random.nextInt() is a method in the java.util.Random class;
• Math.random() is a static method in the java.lang.Math class.

(2) Usage ¹
Generate random numbers of [0,n)

//Random.nextInt()
Random r = new Random();
int r = random.nextInt(n);

//Math.random()
int res = (int)(Math.random() * n);

(3) Summary ¹

• The Math.random() method generates a double type random number in the range [0, 1); the nextXxxx series methods in the Random class generate a random number from 0 to n;
• Math.random() is thread-safe and can be called in a multi-threaded environment;
• If there is no special requirement, use (int)(Math.random()*n) to generate random numbers.

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1. csdn-basic usage of random.nextInt and Math.random ↩︎ ↩︎ ↩︎