Java Java.util.Random.nextInt()用法及代码示例

生成随机数本身具有良好的实用价值，并且通过使用函数实现随机数可以证明是非常有用的。 Java在其语言中已经将整个库专用于随机数，从而看到了它在日常编程中的重要性。本文讨论了nextInt()。

1. java.util.Random.nextInt()：nextInt()用于从此随机数生成器的序列中获取下一个随机整数值。

   Declaration:
   public int nextInt()
   参数：
   NA
   返回值：
   The method call returns the next integer number from the sequence
   Exception:
   NA
   

   以下示例显示了java.util.Random.nextInt()的用法

   
   

   // Java code to demonstrate the working 
   // of nextInt() 
   import java.util.*; 
   public class NextInt1 { 
       public static void main(String[] args) 
       { 
     
           // create random object 
           Random ran = new Random(); 
     
           // generating integer 
           int nxt = ran.nextInt(); 
     
           // Printing the random Number 
           System.out.println 
           ("The Randomly generated integer is:" + nxt); 
       } 
   }

   输出：

   The Randomly generated integer is:-2052834321
   

2. java.util.Random.nextInt(int n)：nextInt(int n)用于获取介于0(含)和此参数(n)中所传递的数字(不包括)之间的随机数。

   Declaration:
   public int nextInt(int n)
   参数：
   n: This is the bound on the random number to be returned. Must be positive.
   返回值：
   Returns a random number.
   between 0 (inclusive) and n (exclusive).
   Exception:
   IllegalArgumentException: This is thrown if n is not positive.
   

   下面的示例显示java.util.Random.nextInt(int n)的用法

   // Java code to demonstrate the working 
   // of nextInt(n) 
   import java.util.*; 
   public class NextInt2 { 
       public static void main(String args[]) 
       { 
     
           // create random object 
           Random ran = new Random(); 
     
           // Print next int value 
           // Returns number between 0-9 
           int nxt = ran.nextInt(10); 
     
           // Printing the random number  
           // between 0 and 9 
           System.out.println 
           ("Random number between 0 and 10 is:" + nxt); 
       } 
   }

   输出：

   Random number between 0 and 9 is:4
   

IllegalArgumentException：当传递的参数不是正数时，会发生这种情况。
一个示例说明当n不是正数时生成的异常：

// Java code to demonstrate the Exception 
// of nextInt(n) 
import java.util.*; 
public class NextInt2 { 
    public static void main(String[] args) 
    { 
  
        // create random object 
        Random ran = new Random(); 
  
        // generating number between 0 and -12345 
        // Raises Runtime error, as n is negative. 
        int nxt = ran.nextInt(-12345); 
  
        System.out.println 
        ("Generated Random number is:" + nxt); 
    } 
}

运行时错误：

Exception in thread "main" java.lang.IllegalArgumentException:bound must be positive
    at java.util.Random.nextInt(Random.java:388)
    at NextInt2.main(NextInt2.java:14)

Practical Applications

产生随机数有许多应用，无论是彩票，赌博还是小规模游戏。下面展示了一个小型骰子游戏，其中2名玩家掷出6分骰子，第一人获得30分，获胜。

// Java code to demonstrate the Application 
// of nextInt(n) 
import java.util.*; 
public class NextIntAppli { 
    public static void main(String[] args) 
    { 
  
        int sum = 0, sum1 = 0, count = 0, count1 = 0; 
        int turn = 0; 
  
        // creating random object 
        Random ran = new Random(); 
        int flag = 0; 
  
        while (true) { 
            if (turn % 2 == 0) { 
  
                int p1 = ran.nextInt(6); 
                sum += p1; 
                System.out.printf 
                ("Player 1 after turn %d is:%d\n", turn, sum); 
            } 
            else { 
  
                int p2 = ran.nextInt(6); 
                sum1 += p2; 
                System.out.printf 
                ("Player 2 after turn %d is:%d\n", turn, sum1); 
            } 
            if (sum >= 30) { 
                flag = 1; 
                break; 
            } 
            if (sum1 >= 30) { 
                flag = 2; 
                break; 
            } 
            turn++; 
        } 
        if (flag == 1) 
            System.out.println("\nPlayer 1 WON!!"); 
        else
            System.out.println("\nPlayer 2 WON!!"); 
    } 
}

输出：

Player 1 after turn 0 is:0
Player 2 after turn 1 is:4
Player 1 after turn 2 is:2
Player 2 after turn 3 is:9
Player 1 after turn 4 is:5
Player 2 after turn 5 is:9
Player 1 after turn 6 is:6
Player 2 after turn 7 is:14
Player 1 after turn 8 is:8
Player 2 after turn 9 is:18
Player 1 after turn 10 is:12
Player 2 after turn 11 is:21
Player 1 after turn 12 is:13
Player 2 after turn 13 is:26
Player 1 after turn 14 is:18
Player 2 after turn 15 is:29
Player 1 after turn 16 is:18
Player 2 after turn 17 is:34
Player 2 WON!!