Sort arrays and collections isJava 8 lambdaAn amazing application we can implement aComparatorsto implement various sorting.
See the following cases:
static class Person {
final String firstName;
final String lastName;
Person(String firstName, String lastName) {
= firstName;
= lastName;
}
@Override
public String toString() {
return "Person{" +
"firstName='" + firstName + '\'' +
", lastName='" + lastName + '\'' +
'}';
}
}
Person's data are:
List<Person> people =
(
new Person("Jane", "Henderson"),
new Person("Michael", "White"),
new Person("Henry", "Brighton"),
new Person("Hannah", "Plowman"),
new Person("William", "Henderson")
);
We want to sort by name(last name), and then according to the last name (first name) sort.
Before Java 7, we usually implemented a Comparator:
(new Comparator<Person>() {
@Override
public int compare(Person o1, Person o2) {
int result = ();
if (result == 0)
result = ();
return result;
}
});
(::println);
In Java 8, we can use lambda instead of anonymous functions, as follows:
Comparator<Person> c = (p, o) -> (); c = ((p, o) -> ()); (c); (::println);
Here,Lambdaexpression (p, o) -> ()Replace the previous anonymous functionnew Comparator<Person>() {}
becauseJavaThe compiler cannot delay theLambdaExpression type judgment, such as delay tocomparatorPass tosort()method, so we do chainingComparatorWriting is a bit difficult.
For example, we want to write it as follows:
((p, o) -> ())
.thenComparing((p, o) -> ())
In other words, type judgment is from left to right, not from right to left, we can make type inference by creating a generic:
class Utils {
static <E> Comparator<E> compare() {
return (e1, e2) -> 0;
}
}
Through the above compare() method, we can write a smooth comparator chain:
(
Utils.<Person>compare()
.thenComparing((p, o) ->
())
.thenComparing((p, o) ->
())
);
(::println);
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