具有多个字段的对象的Java Comparator [英] Java Comparator for Objects with multiple fields

问题描述

我有一个包含5个字段的对象集合：

I have an Object Collection with 5 fields:

id;
entityType;
entityId;
brandId;
productId;

排序 ArrayList Collection 我写了以下 Comparaor 。

Comparator<Collection> collectionComparator = new Comparator<Collection>() {

    @Override
    public int compare(Collection collection1, Collection collection2) {
        if(collection1.getId().equals(collection2.getId())) {
            if(collection1.getEntityType().equals(collection2.getEntityType())) {
                if(collection1.getEntityId().equals(collection2.getEntityId())) {
                    if(collection1.getBrandId().equals(collection2.getBrandId())) {
                        return collection1.getProductId().compareTo(collection2.getProductId());
                    } else {
                        return collection1.getBrandId().compareTo(collection2.getBrandId());
                    }
                } else {
                    return collection1.getEntityId().compareTo(collection2.getEntityId());
                }
            } else {
                return collection1.getEntityType().compareTo(collection2.getEntityType());
            }
        } 

        return collection1.getId().compareTo(collection2.getId());
    }
};

这是实施 Comparator的正确方法在具有多个要比较的字段的对象上？

Is this the right way to implement Comparator on the object which has multiple fields to compare?

推荐答案

您的方法可能正确，但效率低（不必要地调用equals）而且难以阅读。它可以改写如下：

Your method might be correct, but it is inefficient (unnecessarily calls equals) and difficult to read. It could be rewritten something like this:

public int compare(Collection c1, Collection c2)
{
    int n;
    n = c1.id.compareTo(c2.id);
    if (n != 0) return n;
    n = c1.entityType.compareTo(c2.entityType);
    if (n != 0) return n;
    n = c1.brandId.compareTo(c2.brandId);
    if (n != 0) return n;
    return c1.productId.compareTo(c2.productId);
}

更好的方法是使用一种库方法，将所有这些逻辑抽象出去，这样你就可以了不必考虑它。例如。使用 apache.commons.lang CompareToBuilder

Even better is to use a library method which abstracts all this logic away so you don't have to think about it. E.g. using apache.commons.lang CompareToBuilder

public int compare(Collection c1, Collection c2)
{
    return new CompareToBuilder()
            .append(c1.id, c2.id)
            .append(c1.entityType, c2.entityType)
            .append(c1.brandId, c2.brandId)
            .append(c1.productId, c2.productId)
            .toComparison();
}

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