找出对象列表是否包含具有指定字段值的内容? [英] Finding out if a list of Objects contains something with a specified field value?

问题描述

我有一个从数据库收到的 DTO 列表，它们有一个 ID.我想确保我的列表包含具有指定 ID 的对象.显然，在这种情况下创建具有预期字段的对象无济于事，因为 contains() 调用 Object.equals()，并且它们不会相等.

I have a list of DTO received from a DB, and they have an ID. I want to ensure that my list contains an object with a specified ID. Apparently creating an object with expected fields in this case won't help because contains() calls for Object.equals(), and they won't be equal.

我想出了一个这样的解决方案:创建一个接口 HasId，在我所有的 DTO 中实现它，并用一个具有 contains(Long id) 的新类继承 ArrayList代码>方法.

I came up to a solution like so: created an interface HasId, implemented it in all my DTOs, and inherited ArrayList with a new class that has contains(Long id) method.

public interface HasId {
    void setId(Long id);
    Long getId();
}

public class SearchableList<T extends HasId> extends ArrayList<T> {
    public boolean contains(Long id) {
        for (T o : this) {
            if (o.getId() == id)
                return true;
        }
        return false;
    }
}

但在这种情况下，我无法将 List 和 ArrayList 类型转换为 SearchableList ...我愿意接受，但想确保我不是在发明轮子.

But in this case I can't typecast List and ArrayList to SearchableList... I'd live with that, but wanted to make sure that I'm not inventing the wheel.

编辑(2016 年 10 月):

EDIT (Oct '16):

当然，随着 Java 8 中 lambdas 的引入，实现这一点的方法很简单:

Of course, with the introduction of lambdas in Java 8 the way to do this is straightforward:

list.stream().anyMatch(dto -> dto.getId() == id);

推荐答案

我建议像你写的那样创建简单的静态方法，不需要任何额外的接口:

I propose to create simple static method like you wrote, without any additional interfaces:

public static boolean containsId(List<DTO> list, long id) {
    for (DTO object : list) {
        if (object.getId() == id) {
            return true;
        }
    }
    return false;
}

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