java入门第三季——随机字符串排序

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package com.project4;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class CollectionsTest {
    private static Random randGen = null;
    private static char[] numbersAndLetters = null;
    public void testSort(){
        List<Integer> integerList = new ArrayList<Integer>();
        Random random = new Random();
        Integer k;
        for(int i = 0;i<10;i++){
            do{
                k=random.nextInt(100);
            }while(integerList.contains(k));
            integerList.add(k);
        }
        System.out.println("-----------------排序前----------------");
        for (Integer integer : integerList) {
            System.out.println("元素"+integer);
        }
        Collections.sort(integerList);
        System.out.println("-----------------排序后----------------");
        for (Integer integer : integerList) {
            System.out.println("元素"+integer);
        }
    }
    public void testSort2(){
        List<String> stringList = new ArrayList<String>();
        String k = null;
        Random random = new Random();
        for(int i = 0;i<10;i++){
            int l = random.nextInt(10);
            if(l==0){
                i--;
                continue;
            }
            do{     
                    k=randomString(l);
            }while(stringList.contains(k));
            stringList.add(k);
        }
        System.out.println("-----------------排序前----------------");
        for (String integer : stringList) {
            System.out.println("元素"+integer);
        }
        Collections.sort(stringList);
        System.out.println("-----------------排序后----------------");
        for (String integer : stringList) {
            System.out.println("元素"+integer);
        }
    }
    public static final String randomString(int length) {
        if (length < 1) {
            return null;
        }
        if (randGen == null) {
               randGen = new Random();
               numbersAndLetters = ("0123456789abcdefghijklmnopqrstuvwxyz" +
                  "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ").toCharArray();
                 //numbersAndLetters = ("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ").toCharArray();
                }
        char [] randBuffer = new char[length];
        for (int i=0; i<randBuffer.length; i++) {
            randBuffer[i] = numbersAndLetters[randGen.nextInt(71)];
         //randBuffer[i] = numbersAndLetters[randGen.nextInt(35)];
        }
        return new String(randBuffer);
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        CollectionsTest ak47 = new CollectionsTest();
        //ak47.testSort();
        ak47.testSort2();
    }

}