Collections.sort()方法，字符排序

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

public class CollectionsTest {
    public void testSort3() {
        StringBuilder st = new StringBuilder();//构建StringBuilder类
        List<String> stringlist = new ArrayList<String>();
        String str = "0123456789abcdefghijklmnobqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
        for (int i = 0; i < 10; i++) {//10条字符串
            Random random = new Random();
            do {
                for (int j = 0; j < random.nextInt(9) + 1; j++) {//建立10长度以内的字符串
                    int k = random.nextInt(61);
                    st.append(str.charAt(k));
                }
        //防止字符串重复，并且把st转化为String类，使其满足泛型，被contains方法调用
            } while (stringlist.contains(st.toString()));
            stringlist.add(st.toString());
            st = new StringBuilder();//重新构造st，防止其接着加字符，起到让st字符串"清零"的作用
        }
        System.out.println("------排序前------");
        for (String string : stringlist) {
            System.out.println("元素：" + string);
        }
        Collections.sort(stringlist);
        System.out.println("------排序后------");
        for (String string : stringlist) {
            System.out.println("元素：" + string);
        }
    }
}
public static void main(String[] args) {
        CollectionsTest ct = new CollectionsTest();
        ct.testSort3();
    }