Java Java.util.Random.nextInt()用法及代碼示例

生成隨機數本身具有良好的實用價值，並且通過使用函數實現隨機數可以證明是非常有用的。 Java在其語言中已經將整個庫專用於隨機數，從而看到了它在日常編程中的重要性。本文討論了nextInt()。

1. java.util.Random.nextInt()：nextInt()用於從此隨機數生成器的序列中獲取下一個隨機整數值。

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

   以下示例顯示了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); 
       } 
   }

   輸出：

   The Randomly generated integer is:-2052834321
   

2. java.util.Random.nextInt(int n)：nextInt(int n)用於獲取介於0(含)和此參數(n)中所傳遞的數字(不包括)之間的隨機數。

   Declaration:
   public int nextInt(int n)
   參數：
   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.
   

   下麵的示例顯示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); 
       } 
   }

   輸出：

   Random number between 0 and 9 is:4
   

IllegalArgumentException：當傳遞的參數不是正數時，會發生這種情況。
一個示例說明當n不是正數時生成的異常：

// 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); 
    } 
}

運行時錯誤：

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

產生隨機數有許多應用，無論是彩票，賭博還是小規模遊戲。下麵展示了一個小型骰子遊戲，其中2名玩家擲出6分骰子，第一人獲得30分，獲勝。

// 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!!"); 
    } 
}

輸出：

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!!