Java 常用的转换、排序

1 字符串、数组、集合的转换

定义字符串数组 string[] strarr

string[] strarr = {"red", "green", "blue"};

1.1 字符串数组转集合

list<string> list = arrays.aslist(strarr);

1.2 字符串集合转数组

string[] strarrnew = list.toarray(new string[0]);

1.3 字符串集合转逗号分隔的字符串

string str = string.join(",", list);

1.4 逗号分隔的字符串转字符串集合

list<string> list2 = new arraylist<>(arrays.aslist(str.split(",")));

1.5 对象集合转 map<string, integer>

定义对象 person

private static class person {
    private string name;
    private integer age;
}

定义对象 person 的集合 list

list<person> personlist = lists.newarraylist(
    new person("jordan", 38),
    new person("o'neal", 34),
    new person("james", 31),
    new person("kobe", 34),
    new person("trace", 32)
);

对象集合转为 map

map<string, integer> personmap = personlist.stream().collect(collectors.tomap(person::getname, person::getage));

2 list、map 的排序

2.1 list 自然排序

list.sort(comparator.naturalorder());

2.2 list 按 age 倒序

personlist.sort(comparator.comparing(person::getage).reversed());

2.3 map<string, integer> 按 value 倒序

personmap.entryset().stream()
    .sorted(map.entry.comparingbyvalue(comparator.reverseorder()))
    .collect(collectors.tomap(map.entry::getkey, map.entry::getvalue, (o, n) -> o, linkedhashmap::new));