Two ways in which Java produces random numbers

In Java, there are two ways to get random numbers (generating a random number) is a familiar java.lang.Math.Random () static method, and the other is to create Java.util.Random objects. The following are the procedures used for two methods:

I. Java.lang.Math.random ()

When using this static method, we do not need to import any packages, because the java.lang.* package is loaded by default, and the following example uses the method:

public class RandomTest{
　　public static void main(String[] args){
　　　　int i=Math.random();//random()会自动产生一个0.0-1.0的双精度随机数
　　　　System.out.println(i);//输出
　　　　i=Math.random()*1000;//产生0-1000的双精度随机数　
　　　　System.out.println(i);
　　　　int b=(int)(Math.random()*1000);//产生0-1000的整数随机数　
　　　　System.out.println(b);
　　}
}

Two. Create a Java.util.Random object

import java.util.random
public class RandomTest{
　　public static void main(String[] args){
　　　　Random random=new Random();//创建random对象
　　　　int intNumber=random.nextInt();//获取一个整型数
　　　　float floatNumber=random.nextFloat();//获取一个浮点数(0-1)
　　　　double doubleNumber=random.nextDouble();//获取双精度数(0-1)
　　　　boolean booleanNumber=random.nextBoolean();//获取boolean数
　　　　System.out.println("intNumber:"+intNumber);
　　　　System.out.println("floatNumber:"+floatNumber);
　　　　System.out.println("doubleNumber:"+doubleNumber);
　　　　System.out.println("booleanNumber:"+booleanNumber);
　　}
}

Random use the current time as the cardinality when generating random numbers, we can system.currenttimemillis () to get the cardinality. Of course we can also specify the cardinality:

Random random=new Random (100);

The sequence of random numbers produced by the same cardinality is the same, which can be verified by the following procedure:

import java.util.random
public class RandomTest{
　　public static void main(String[] args){
　　　　Random random1=new Random(100);
　　　　Random random2=new Random(100);
　　　　for(int i=0;i<5;i++){
　　　　　　System.out.print(random1.nextInt()+"\t");
　　　　　　System.out.println(random2.nextInt()+"\t");
　　　　　　System.out.println("---------------------------------");
　　　　}
　　}
}

We can see that the random numbers produced by RANDOM1 and Random2 are the same.