TestRandom.java

import java.util.*;

class TestRandom {
      // 從 m個整數中隨機抽取 n個整數，條件: m > n
      public static int[] genRandomArray(int m , int n) {
          if(m<=0) return null;
          if(n<=0) return null;
          if(m< n) return null;
          
           int[] intRet = new int[n]; 
           int intRd = 0; // 存放隨機數
           int count = 0; // 記錄生成的隨機數個數
           boolean flag = false;  // 是否已經生成過標誌
           while(count< n){
                Random rdm = new Random(System.currentTimeMillis());
                intRd = Math.abs(rdm.nextInt())%m +1;
                for(int i=0;i<count;i++){
                    if(intRet[i]==intRd){
                        flag = true;
                        break;
                    }else{
                        flag = false;
                    }
                }
                if(flag==false){
                    intRet[count] = intRd;
                    count++;
                }
          }
          return intRet;
      }
       
      public static void main(String[] args) {
          int m=0,n=0;
          if(args.length ==2){
              m = Integer.parseInt(args[0]);
              n = Integer.parseInt(args[1]);
          } else {
              System.out.println(" usage: java TestRandom m n ");
              return;
          }
          int[] ar = genRandomArray(m,n);
          if(ar==null){
              System.out.println(" Error: int array is null ");
              return;
          }
          for(int i=0; i<n; i++){
            System.out.print(" "+ar[i]);
          }
     }
}