java - 如何从包含键 String 和 list<Object> 的 hashmap 中仅获取一个值

Question

如何从包含键字符串和列表的 hashmap 中仅获取一个值

HashMap :

HashMap<String, ArrayList<Person>> person = new HashMap<String, ArrayList<Person>>();

构造函数人:

Person(int phone, String mail){
    this.phone = phone;
    this.mail = mail;
}

获取对象的方法:

protected void findObject(String lname){
    if (person.containsKey(lname)) {
            System.out.println(lname + " phone: " + person.get(lname));
    }
}

但我需要两种方法:

protected void findPhone(String lname){
//should get only phone from Person;
}

protected void findMail(String mail){
//should get only mail from Person;
}

像这样工作:

protected List<Integer> findPhone(String lname) {
    List<Integer> listPhone = null;
    if (person.containsKey(lname)) {
        listPhone = person.get(lname).stream()
        .map(Person::getPhone)
        .collect(Collectors.toList());

    }
    return listPhone;
}

protected List<String> findMail(String lname) {
    List<String> listMail = null;
    if (person.containsKey(lname)) {
        listMail = person.get(lname).stream()
        .map(Person::getPhone)
        .collect(Collectors.toList());

    }
    return listmail;
}

Answer 1

如果您使用的是 Java 8，您可以使用:

protected void findPhone(String lname) {
    if (person.containsKey(lname)) {
        List<Integer> listPhone = person.get(lname).stream()
                .map(Person::getPhone)
                .collect(toList());
    }
}

和

protected void findMail(String lname) {
    if (person.containsKey(lname)) {
        List<String> listMails = person.get(lname).stream()
                .map(Person::getMail)
                .collect(toList());
    }
}