在集合中查找具有给定属性的所有对象 [英] Finding all objects that have a given property inside a collection

问题描述

我有一些复杂的对象，比如一个 Cat，它有很多属性，比如年龄、最喜欢的猫食等等.

I have some complicated object, such as a Cat, which has many properties, such as age, favorite cat food, and so forth.

Java 集合中存储了一堆猫，我需要找到所有 3 岁的猫，或者最喜欢猫食是 Whiskas 的猫.当然，我可以编写一个自定义方法来查找具有特定属性的 Cats，但是这对于许多属性来说变得很麻烦；有没有一些通用的方法来做到这一点?

A bunch of Cats are stored in a Java Collection, and I need to find all the Cats that are aged 3, or those whose favorite cat food is Whiskas. Surely, I can write a custom method that finds those Cats with a specific property, but this gets cumbersome with many properties; is there some generic way of doing this?

推荐答案

您可以编写一个方法，该方法接受一个接口的实例，该接口定义了一个 check(Cat) 方法，该方法可以是使用您想要的任何属性检查实现.

You could write a method that takes an instance of an interface which defines a check(Cat) method, where that method can be implemented with whatever property-checking you want.

更好的是，让它通用:

public interface Checker<T> {
    public boolean check(T obj);
}

public class CatChecker implements Checker<Cat> {
    public boolean check(Cat cat) {
        return (cat.age == 3); // or whatever, implement your comparison here
    }
}

// put this in some class
public static <T> Collection<T> findAll(Collection<T> coll, Checker<T> chk) {
    LinkedList<T> l = new LinkedList<T>();
    for (T obj : coll) {
         if (chk.check(obj))
             l.add(obj);
    }
    return l;
}

当然，正如其他人所说，这就是关系数据库的用途...

Of course, like other people are saying, this is what relational databases were made for...

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