JDK8之四大核心函数式接口

四大核心函数式接口

Consumer 接口

1. 接口说明
   Consumer 接口是消费性接口，无返回值。Java8 中对 Consumer 的定义如下所示。

/** * Represents an operation that accepts a single input argument and returns no * result. Unlike most other functional interfaces, {@code Consumer} is expected * to operate via side-effects. * * <p>This is a <a href="package-summary.html">functional interface</a> * whose functional method is {@link #accept(Object)}. * * @param <T> the type of the input to the operation * * @since 1.8 */@FunctionalInterfacepublicinterfaceConsumer<T>{/** * Performs this operation on the given argument. * * @param t the input argument */voidaccept(Tt);/** * Returns a composed {@code Consumer} that performs, in sequence, this * operation followed by the {@code after} operation. If performing either * operation throws an exception, it is relayed to the caller of the * composed operation. If performing this operation throws an exception, * the {@code after} operation will not be performed. * * @param after the operation to perform after this operation * @return a composed {@code Consumer} that performs in sequence this * operation followed by the {@code after} operation * @throws NullPointerException if {@code after} is null */defaultConsumer<T>andThen(Consumer<?superT>after){Objects.requireNonNull(after);return(Tt)->{accept(t);after.accept(t);};}

使用说明

publicvoidhandlerConsumer(Integernumber,Consumer<Integer>consumer){consumer.accept(number);}@Testpublicvoidtest1(){this.handlerConsumer(10000,(i)->System.out.println(i));}

Supplier 接口

1. 接口说明
   Supplier 接口是供给型接口，有返回值，Java8 中对 Supplier 接口的定义如下所示。

@FunctionalInterfacepublicinterfaceSupplier<T>{Tget();}

使用示例

publicList<Integer>getNumberList(intnum,Supplier<Integer>supplier){List<Integer>list=newArrayList<>();for(inti=0;i<num;i++){list.add(supplier.get())}returnlist;}@Testpublicvoidtest2(){List<Integer>numberList=this.getNumberList(10,()->newRandom().nextInt(100));numberList.stream().forEach(System.out::println);}

Function 接口

1. 接口说明
   Function 接口是函数型接口，有返回值，Java8 中对 Function 接口的定义如下所示。

@FunctionalInterfacepublicinterfaceFunction<T,R>{Rapply(Tt);default<V>Function<V,R>compose(Function<?superV,?extendsT>before){Objects.requireNonNull(before);return(Vv)->apply(before.apply(v));}default<V>Function<T,V>andThen(Function<?superR,?extendsV>after){Objects.requireNonNull(after);return(Tt)->after.apply(apply(t));}static<T>Function<T,T>identity(){returnt->t;}}

使用示例

publicStringhandlerString(Stringstr,Function<String,String>func){returnfunc.apply(str);}@Testpublicvoidtest3(){Stringstr=this.handlerString("binghe",(s)->s.toUpperCase());System.out.println(str);}

Predicate 接口

1. 接口说明
   Predicate 接口是断言型接口，返回值类型为 boolean，Java8 中对 Predicate 接口的定义如下所示。

@FunctionalInterfacepublicinterfacePredicate<T>{booleantest(Tt);defaultPredicate<T>and(Predicate<?superT>other){Objects.requireNonNull(other);return(t)->test(t)&&other.test(t);}defaultPredicate<T>negate(){return(t)->!test(t);}defaultPredicate<T>or(Predicate<?superT>other){Objects.requireNonNull(other);return(t)->test(t)||other.test(t);}static<T>Predicate<T>isEqual(ObjecttargetRef){return(null==targetRef)?Objects::isNull:object->targetRef.equals(object);}}

使用示例

publicList<String>filterString(List<String>list,Predicate<String>predicate){List<String>strList=newArrayList<>();for(Stringstr:list){if(predicate.test(str)){strList.add(str);}}returnstrList;}@Testpublicvoidtest4(){List<String>list=Arrays.asList("Hello","Lambda","binghe","lyz","World");List<String>strList=this.filterString(list,(s)->s.length()>=5);strList.stream().forEach(System.out::println);}