Java 8：如何从列表中的 object 中获取属性，其中 object 的其他属性必须与输入匹配

Question

class Person{
     String Name;
     String Id;
    }

I have a list of person. I want to get the id of a person where the Name matches with input, I know it can be done by using filter but in my case, name is always unique so I get only one ID back. Please let me know if there is any other efficient ways to do this.

Answer 1

If you are going to query on name many times you could keep a map around that maps a Person to a name (and that's assuming your names are indeed unique).

Map<String, Person> byName = new HashMap<>();
yourList.forEach(person -> byName.put(person.name, person));

and then lookup the person directly by name:

Person person = byName.get("a name");
if (person != null) {
...
}

Answer 2

Since the name is unique, you could use the short-circuiting terminal operation findFirst after the filter . This would allow the stream processing to stop as soon as a match is encountered.

return list.stream()
           .filter(p -> p.getName().equals(input))
           .findFirst() // Optional<Person> is returned
           .map(Person::getId)
           .orElse(null);// if no matching name is found