1向ListString ls中放入50个随机的大写英文字母2按照从小到大排序打印排序结果3按照从大道小排序打印排序结果4操作排序后的ls去掉重复的字母打印去重后的结果5去重后判断是否包含全部的26个字母缺少哪几个

1）将50个随机的大写英文字母放入List ls中：

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

public class Main {
    public static void main(String[] args) {
        List<String> ls = new ArrayList<>();
        Random random = new Random();
        for (int i = 0; i < 50; i++) {
            char c = (char) (random.nextInt(26) + 'A');
            ls.add(String.valueOf(c));
        }
    }
}

2）按照从小到大排序，打印排序结果：

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

public class Main {
    public static void main(String[] args) {
        List<String> ls = new ArrayList<>();
        Random random = new Random();
        for (int i = 0; i < 50; i++) {
            char c = (char) (random.nextInt(26) + 'A');
            ls.add(String.valueOf(c));
        }

        Collections.sort(ls);
        for (String s : ls) {
            System.out.println(s);
        }
    }
}

3）按照从大到小排序，打印排序结果：

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

public class Main {
    public static void main(String[] args) {
        List<String> ls = new ArrayList<>();
        Random random = new Random();
        for (int i = 0; i < 50; i++) {
            char c = (char) (random.nextInt(26) + 'A');
            ls.add(String.valueOf(c));
        }

        Collections.sort(ls, Collections.reverseOrder());
        for (String s : ls) {
            System.out.println(s);
        }
    }
}

4）去掉重复的字母，打印去重后的结果：

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

public class Main {
    public static void main(String[] args) {
        List<String> ls = new ArrayList<>();
        Random random = new Random();
        for (int i = 0; i < 50; i++) {
            char c = (char) (random.nextInt(26) + 'A');
            ls.add(String.valueOf(c));
        }

        Collections.sort(ls);
        for (String s : ls) {
            System.out.println(s);
        }

        Set<String> set = new HashSet<>(ls);
        ls.clear();
        ls.addAll(set);
        System.out.println("去重后的结果：");
        for (String s : ls) {
            System.out.println(s);
        }
    }
}

5）去重后，判断是否包含全部的26个字母，缺少哪几个：

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

public class Main {
    public static void main(String[] args) {
        List<String> ls = new ArrayList<>();
        Random random = new Random();
        for (int i = 0; i < 50; i++) {
            char c = (char) (random.nextInt(26) + 'A');
            ls.add(String.valueOf(c));
        }

        Collections.sort(ls);
        for (String s : ls) {
            System.out.println(s);
        }

        Set<String> set = new HashSet<>(ls);
        ls.clear();
        ls.addAll(set);
        System.out.println("去重后的结果：");
        for (String s : ls) {
            System.out.println(s);
        }

        String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        for (char c : alphabet.toCharArray()) {
            if (!ls.contains(String.valueOf(c))) {
                System.out.println("缺少字母：" + c);
            }
        }
    }
}
``