Java 8: sort list of objects by attribute without custom comparator

What is the cleanest short way to get this done ?

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 like this:

Collections.sort(list, X.attr);

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最佳答案

Assuming you actually have a List<AnObject>, all you need is

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:

list.sort(Comparator.comparing(AnObject::getAttr));

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As a complement to @JB Nizet's answer, if your attr is nullable,

list.sort(Comparator.comparing(AnObject::getAttr));

may throw a NPE.

If you also want to sort null values, you can consider

    list.sort(Comparator.comparing(a -> a.attr, Comparator.nullsFirst(Comparator.naturalOrder())));

    list.sort(Comparator.comparing(a -> a.attr, Comparator.nullsLast(Comparator.naturalOrder())));

which will put nulls first or last.

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A null-safe option to JB Nizet's and Alex's answer above would be to do the following:

list.sort(Comparator.comparing(AnObject::getAttr, Comparator.nullsFirst(Comparator.naturalOrder())));

list.sort(Comparator.comparing(AnObject::getAttr, Comparator.nullsLast(Comparator.naturalOrder())));