使用 Comparator Interface 和 java 8 Streams 进行排序

Sorting using Comparator Interface and java 8 Streams(使用 Comparator Interface 和 java 8 Streams 进行排序)

问题描述

Parent 是一个由 Child 继承的类.由 GrandChild 继承.每个类都包含子类的列表(即父类包含子类列表，子类包含子类列表).每个类包含 50 个属性(attrib1-atrib50).getChildList() 返回 Child 类型对象的 arrayList getGrandChildList() 返回 GrandChild 类型对象的 arrayList

Parent is a class which is inherited by Child. which is inherited by GrandChild. Each class contains List of the child class(i.e Parent contains List of Child and Child contains List of GrandChild). Each class contains 50 attributes(attrib1-atrib50). getChildList() returns the arrayList of objects of type Child getGrandChildList() returns the arrayList of objects of type GrandChild

设 resultSet 为父列表

Let resultSet be List of Parent

List<Parent> resultSet

现在我想根据一些属性对列表进行排序.例如，如果我想根据两个父属性(比如属性 1 和属性 2)对结果集进行排序，我使用此代码.

Now I want to sort the list based on some attributes. For example if I want to sort resultSet based on two parent attributes(say Attribute 1 and attribute 2, I use this code.

Comparator<Parent> byFirst = (e1, e2) -> e2.getAttrib1().compareTo(e1.getAttrib1());
Comparator<Parent> bySecond = (e1, e2) -> e1.getAttrib2().compareTo(e2.getAttrib2());

Comparator<Parent> byThird = byFirst.thenComparing(bySecond);


List<Parent> sortedList = resultSet.stream().sorted(byThird).collect(Collectors.toList());

现在我想根据 Child 类的属性 1 和 GrandChild 类的属性 1 对 parentlist 进行排序.我应该如何排序.

Now I want to sort the parentlist based on attribute 1 of Child class and attribute 1 of GrandChild class. How should I sort this.

推荐答案

使用 Comparator.comparing 制作比较器.只需弄清楚您要比较的内容.它看起来像这样，除了您将编写任何您想使用的逻辑来提取要比较的值:

Use Comparator.comparing to make the comparators. Just figure out what you want to compare. It will looks something like this, except you will write whatever logic you want to use to extract the values to compare:

Comparator<Parent> byAttr1ofFirstChild = Comparator.comparing(
    parent -> parent.getChildren().get(0).getAttr1()
);

Comparator<Parent> byAttr1ofFirstGrandChild = Comparator.comparing(
    parent -> parent.getChildren().get(0).getGrandChildren().get(0).getAttr1()
);


List<Parent> sortedList = parents.stream()
    .sorted(byAttr1ofFirstChild.thenComparing(byAttr1ofFirstGrandChild))
    .collect(toList());

Comparator.comparing 也会使您问题中的示例更好(使用静态导入):

Comparator.comparing would also make the examples in your question much nicer (using static imports) :

Comparator<Parent> byFirst = comparing(Parent::getAttrib1, reverseOrder());
Comparator<Parent> bySecond = comparing(Parent::getAttrib2);

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