Question

JAVA中，从命令行中输入一个字符串，要求从中随机选择6个字符

Answer 1

package com.test;

import java.util.Random;
import java.util.Scanner;

public class RandomTest {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
System.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();
for(int i=0;i<randomLength;){
int randomNum = rand.nextInt(randomLength);
if(randomNum >= sourceLength){
continue;
}
i++;
System.out.println(randomNum);
result.append(source.charAt(randomNum));
}
System.out.println("随机的6个字符为："+result);
}

}
直接复制可以运行

追问

为什么经常出现一样的随机数呢？

追答

package com.test;

import java.util.HashSet;
import java.util.Random;
import java.util.Scanner;
import java.util.Set;

public class RandomTest {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
System.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 set =new HashSet();
for(int i=0;i= 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);
}

}
这样就可以了。

Answer 2

private static Random randGen = null;
private static char[] numbersAndLetters = null;
public static final String randomString(int length,string TestString) {
        if (length < 1) {
            return null;
        }
        if (randGen == null) {
               randGen = new Random();
               numbersAndLetters = TestString.toCharArray();
                }
        char [] randBuffer = new char[length];
        for (int i=0; i<randBuffer.length; i++) {
            randBuffer[i] = numbersAndLetters[randGen.nextInt(TestString.length-1)];
        }
        return new String(randBuffer);
}

Answer 3

先看看这串字符长度

然后产生6个 这个长度之内的随机数,不重复的

然后用substring输出

Answer 4

x=random
char=charAt（x）