从命令行中输入一个字符串，要求从中随机选择6个字符

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从命令行中输入一个字符串，要求从中随机选择6个字符

import java.io.PrintStream;import java.util.Random;import java.util.Scanner;//从命令行中输入一个字符串，要求从中随机选择6个字符public class RandomDemo {public static void main(String args[]){System.out.print("请输入一行字符串： ");Scanner sc = new Scanner(System.in);String str = sc.next();int sourceLength = str.length();int randomLength = 6;if(sourceLength <0){return;}Random r = new Random();StringBuffer sb = new StringBuffer();for (int i = 0; i<6;){       int randomNum = r.nextInt(randomLength);       if(randomLength >= sourceLength){      continue;        }       i++;      // System.out.print(randomNum);       sb.append(str.charAt(randomNum));    }System.out.println(("随机的6个字符为："+sb));}}

方法二：

避免出现重复的随机数

import java.util.HashSet;import java.util.Random;import java.util.Scanner;import java.util.Set;public class RandomTest {public static void main(String[] args) {// TODO Auto-generated method stubSystem.out.println("请输入字符串：");Scanner scan = new Scanner(System.in);String source = scan.next();int sourceLength = source.length();int randomLength = 6;if(sourceLength < 0){return;}Random rand = new Random();StringBuilder result = new StringBuilder();//存储不重复的随机数Set<Integer> set =new HashSet<Integer>();for(int i=0;i<randomLength;){int randomNum = rand.nextInt(randomLength);System.out.println("随机数为："+randomNum);if(randomNum >= sourceLength || set.contains(randomNum)){System.out.println("set存在随机数:"+randomNum);continue;}i++;set.add(randomNum);System.out.println(randomNum);result.append(source.charAt(randomNum));}System.out.println("随机的6个字符为："+result);}}

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