list java 8，在没有自定义比较器的情况下按属性对对象列表进行排序
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java 8, Sort list of objects by attribute without custom comparator
提问by Nabil Sham
What is the cleanest short way to get this done ?
完成这项工作的最简洁的方法是什么？
class AnObject{
Long attr;
}
List<AnObject> list;
I know it can be done with custom comparator for AnObject. Isn't there something ready out of the box for such case ? kind of
我知道可以使用 AnObject 的自定义比较器来完成。对于这种情况，没有现成的东西吗？的种类
Collections.sort(list, X.attr ) ;
回答by JB Nizet
Assuming you actually have a List<AnObject>, all you need is
假设你真的有一个List<AnObject>，你所需要的就是
list.sort(Comparator.comparing(a -> a.attr));
If you make you code clean by not using public fields, but accessor methods, it becomes even cleaner:
如果您不使用公共字段而是使用访问器方法来使代码干净，它会变得更干净：
list.sort(Comparator.comparing(AnObject::getAttr));
回答by Alex
As a complement to @JB Nizet's answer, if your attr is nullable,
作为@JB Nizet 答案的补充，如果您的属性可以为空，
list.sort(Comparator.comparing(AnObject::getAttr));
may throw a NPE.
可能会抛出 NPE。
If you also want to sort null values, you can consider
如果还想对空值进行排序，可以考虑
list.sort(Comparator.comparing(a -> a.attr, Comparator.nullsFirst(Comparator.naturalOrder())));
or
或者
list.sort(Comparator.comparing(a -> a.attr, Comparator.nullsLast(Comparator.naturalOrder())));
which will put nulls first or last.
这将首先或最后放置空值。
回答by Warren Crasta
A null-safe option to JB Nizet's and Alex's answer above would be to do the following:
上面 JB Nizet 和 Alex 的回答的空安全选项是执行以下操作：
list.sort(Comparator.comparing(AnObject::getAttr, Comparator.nullsFirst(Comparator.naturalOrder())));
or
或者
list.sort(Comparator.comparing(AnObject::getAttr, Comparator.nullsLast(Comparator.naturalOrder())));
