java8笔记

java.util.function里提供了Predicate,Consumer和Function三个函数式接口

Predicate:T->boolean

Consumer:T->{}

Function:T->R

同时提供了多个针对原始类型操作的函数式接口

常用函数式接口

函数是接口	函数描述符	原始类型特化
Predicate<T>	T->boolean	IntPredicate,LongPredicate,DoublePredicate
Consumer<T>	T->void	IntConsumer,LongConsumer,DoubleConsumer
Function<T,R>	T->R	IntFunction<R>,IntToDoubleFunction,IntToLongFunction LongFunction<R>,LongToDoubleFunction,LongToIntFunction DoubleFunction<R>,DoubleToIntFunction,DoubleToLongFunction ToIntFunction<T>,ToLongFunction<T>,ToDoubleFunction<T>
Supplier<T>	()->T	BooleanSupplier,IntSupplier,LongSupplier,DoubleSupplier
UnaryOperator<T>	T->T	IntUnaryOperator,LongUnaryOperator,DoubleUnaryOperator
BinaryOperator<T>	(T,T)->T	IntBinaryOperator,LongBinaryOperator,DoubleBinaryOperator
BiPredicate<L,R>	(L,R)->boolean
BiConsumer<T,U>	(T,U)->void	ObjIntConsumer<T>,ObjLongConsumer<T>,ObjDoubleConsumer<T>
BiFunction<T,U,R>	(T,U)->R	ToIntBiFunction<T,U>,ToLongBiFunction<T,U>,ToDoubleBiFunction<T,U>

比较器复合：

静态方法Comparator.comparing返回一个T->int， .reversed()反转排序，.thenComparing()二次排序

例如按苹果重量递减排序，重量一样得按国家排：

appleList.sort(comparing(Apple::getWeight)).reverse().thenComparing(Apple::getCountry)

谓词接口：

negate(非),or(或),and(与)

运算顺序看作与前面得结果运算，即a.or(b).and(c)=(a || b) && c

复合函数

andThen 和 compose  令Function<Integer,Integer> f = x -> x + 1;Function<Integer,Integer> g = x -> x * 2;

f.andThen(g):f的输出当作g的输入=g(f(x)) = (x+1)*2

f.compose(g): g的输出当作f的输入=f(g(x))=x*2+1

流只能forEach一次