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->boolean	IntPredicate,LongPredicate,DoublePredicate
Consumer	T->void	IntConsumer,LongConsumer,DoubleConsumer
Function	T->R	IntFunction,IntToDoubleFunction,IntToLongFunction LongFunction,LongToDoubleFunction,LongToIntFunction DoubleFunction,DoubleToIntFunction,DoubleToLongFunction ToIntFunction,ToLongFunction,ToDoubleFunction
Supplier	()->T	BooleanSupplier,IntSupplier,LongSupplier,DoubleSupplier
UnaryOperator	T->T	IntUnaryOperator,LongUnaryOperator,DoubleUnaryOperator
BinaryOperator	(T,T)->T	IntBinaryOperator,LongBinaryOperator,DoubleBinaryOperator
BiPredicate	(L,R)->boolean
BiConsumer	(T,U)->void	ObjIntConsumer,ObjLongConsumer,ObjDoubleConsumer
BiFunction	(T,U)->R	ToIntBiFunction,ToLongBiFunction,ToDoubleBiFunction

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 f = x -> x + 1;Function 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