基础内容

1.set集合类型取交集/并集/差集

        String[] str1={"a","b","c","d","e"};
        String[] str2={"d","e","f","g","h"};

        Set<String> set1 = new HashSet<String>(Arrays.asList(str1));
        Set<String> set2 = new HashSet<String>(Arrays.asList(str2));
        Set<String> set = new HashSet<String>();
        System.out.println("集" + set2);
        // 并集
        set.addAll(set1);
        set.addAll(set2);
        System.out.println("并集" + set);

        // 交集
        set.clear();
        set.addAll(set1);
        set.retainAll(set2);
        System.out.println("交集" + set);
        // 差集
        set.clear();
        set.addAll(set1);
        set.removeAll(set2);
        System.out.println("差集" + set);

2.给字符串中每两位字符加一个空格

        String input = "abcdefghijk";
        String regex = "(.{2})";
        input = input.replaceAll (regex, "$1 ");
        System.out.println (input);