隨機數存儲在數組列表中，並從中選擇

Question

我想創建一個程序來生成隨機數並存儲到arraylist。 同時獲取存儲的號碼multiply。

我有存儲生成的號碼，但我怎麼才能真正得到我想要的號碼。 對於這個例子，我試圖得到3rd number，我錯過了哪一步？

public class arraylist { 

    public static void main(String[] args) { 

     List<Integer> list = new ArrayList<Integer>(); 
     Random rand = new Random(); 

     int numtogen; 
     int third; 
     Scanner scan = new Scanner(System.in); 
     System.out.println("How many number do you want to generate: "); 
     numtogen = scan.nextInt(); 
     System.out.println("What number do you want to multiply with the third number: "); 
     third = scan.nextInt(); 

     HashSet<Integer> generated = new HashSet<Integer>(); 

     // Prevent repeat 
     for (int x = 1; x <= numtogen; ++x) { 
      while (true) { 
       // generate a range from 0-100 
       int ranNum = rand.nextInt(100); 

       if (generated.contains(ranNum)) { 

        continue; 
       } else { 
        list.add(ranNum); 
        System.out.println("Number " + x + "=" + " = " + ranNum); 
        break; 
       } 

      } 

     } 
     int numinlist; 
     while (!list.isEmpty()) { 

      // Integer[] numlist= numbinlist.hasNextInt; 

      // int answer = numlist[2]*third; 
      // System.out.println("Answer to first number = "+answer); 
     } 
    } 

} 

Answer 1

你可以不重複數字的生成更改爲：

Set<Integer> generated = new LinkedHashSet<Integer>(); 
// Prevent repeat 
while (generated.size() < numtogen) { 
    generated.add(rand.nextInt(100)); 
} 
List<Integer> list = new ArrayList<Integer>(generated); 

我瞭解你的實際問題，並知道答案，我會盡快修改這個答案。

Answer 2

如果你想獲得第三生成的數字試試這個：

int number = list.get(2); 

Answer 3

改變這一點：

for (int x = 1; x <= numtogen; ++x) { 
    while (true) { 
     // generate a range from 0-100 
     int ranNum = rand.nextInt(100); 

     if (generated.contains(ranNum)) { 

      continue; 
     } else { 
      list.add(ranNum); 
      System.out.println("Number " + x + "=" + " = " + ranNum); 
      break; 
     } 
    } 
} 

到：

for (int x = 1; x <= numtogen; ++x) { 
    // generate a range from 0-100 
    int ranNum = rand.nextInt(100); 
    if (generated.contains(ranNum)) { 
     continue; 
    } else { 
     list.add(ranNum); 
     System.out.println("Number " + x + "=" + " = " + ranNum); 
    } 
} 

然後，所有你需要做的訪問第三個號碼是這樣的：

int answer = (list.get(2) * third);