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Java 8 新特性:5-Supplier、IntSupplier、BinaryOperator接口
(原)
这个接口很简单,里面只有一个抽象方法,没有default和静态方法。
/* * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.util.function; /** * Represents a supplier of results. *代表了一个供应的结果 * <p>There is no requirement that a new or distinct result be returned each * time the supplier is invoked. * 没有要求supplier 被调用以后都需要返回一个新的或者不同的结果 * <p>This is a <a href="http://www.mamicode.com/package-summary.html">functional interface</a> * whose functional method is {@link #get()}. *这是一个方法为get的函数式接口 * @param <T> the type of results supplied by this supplier * * @since 1.8 */ @FunctionalInterface public interface Supplier<T> { /** * Gets a result. * * @return a result */ T get(); }
如果前面几篇看过了,那么这个会很简单。不接收参数,返回的类型随调用者控制,这个有点类似于不接收参数的工厂模式。
然后有一个与之相关的,返回int类型的函数式接口,叫IntSupplier,
它里面的方法是这样的。
/* * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.util.function; /** * Represents a supplier of {@code int}-valued results. This is the * {@code int}-producing primitive specialization of {@link Supplier}. * * <p>There is no requirement that a distinct result be returned each * time the supplier is invoked. * * <p>This is a <a href="http://www.mamicode.com/package-summary.html">functional interface</a> * whose functional method is {@link #getAsInt()}. * * @see Supplier * @since 1.8 */ @FunctionalInterface public interface IntSupplier { /** * Gets a result. * * @return a result */ int getAsInt(); }
IntSupplier 和Supplier差不多,只不过它限定了返回值为int类型。
由于这个篇幅过短,跳跃性的再介绍一个接口BinaryOperator
/* * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.util.function; import java.util.Objects; import java.util.Comparator; /** * Represents an operation upon two operands of the same type, producing a result * of the same type as the operands. This is a specialization of * {@link BiFunction} for the case where the operands and the result are all of * the same type. * * <p>This is a <a href="http://www.mamicode.com/package-summary.html">functional interface</a> * whose functional method is {@link #apply(Object, Object)}. * * @param <T> the type of the operands and result of the operator * * @see BiFunction * @see UnaryOperator * @since 1.8 */ @FunctionalInterface public interface BinaryOperator<T> extends BiFunction<T,T,T> { /** * Returns a {@link BinaryOperator} which returns the lesser of two elements * according to the specified {@code Comparator}. * * @param <T> the type of the input arguments of the comparator * @param comparator a {@code Comparator} for comparing the two values * @return a {@code BinaryOperator} which returns the lesser of its operands, * according to the supplied {@code Comparator} * @throws NullPointerException if the argument is null */ public static <T> BinaryOperator<T> minBy(Comparator<? super T> comparator) { Objects.requireNonNull(comparator); return (a, b) -> comparator.compare(a, b) <= 0 ? a : b; } /** * Returns a {@link BinaryOperator} which returns the greater of two elements * according to the specified {@code Comparator}. * * @param <T> the type of the input arguments of the comparator * @param comparator a {@code Comparator} for comparing the two values * @return a {@code BinaryOperator} which returns the greater of its operands, * according to the supplied {@code Comparator} * @throws NullPointerException if the argument is null */ public static <T> BinaryOperator<T> maxBy(Comparator<? super T> comparator) { Objects.requireNonNull(comparator); return (a, b) -> comparator.compare(a, b) >= 0 ? a : b; } }
由于之前花了大篇幅讲过Function,BiFunction,这个doc就不解释。直接看源码。
BinaryOperator<T> extends BiFunction<T,T,T>
BinaryOperator继承于BiFunction ,我们知道BiFunction是接收二个参数,返回一个结果,而BinaryOperator只有一个参数T,那么它的方法apply的传入参数和返回结果都是相同类型。它里面有二个静态方法,minBy和maxBy用来作比较的。minBy比较出较大的一个,maxBy比较出较小的一个。
下面给个例子测试一下结果。
package com.demo.jdk8; import java.util.Comparator; import java.util.function.BinaryOperator; import java.util.function.IntSupplier; import java.util.function.Supplier; public class Test5 { public static void main(String[] args) { System.out.println("part1---------------------"); Supplier<Test5Class> s = () -> new Test5Class("hello", 14); System.out.println(s.get().getName() + "=" + s.get().getAge()); System.out.println("part2---------------------"); IntSupplier ss = () -> 99; System.out.println(ss.getAsInt()); System.out.println("part3---------------------"); System.out.println(getMin(3,6 , (a,b) -> a - b)); System.out.println("part4---------------------"); System.out.println(getMax(3,6 , (a,b) -> a - b)); } public static int getMin(int a ,int b,Comparator<Integer> c){ return BinaryOperator.minBy(c).apply(a, b); } public static int getMax(int a ,int b,Comparator<Integer> c){ return BinaryOperator.maxBy(c).apply(a, b); } } class Test5Class{ private String name; private int age; public Test5Class(String name,int age){ this.name = name; this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } }
Java 8 新特性:5-Supplier、IntSupplier、BinaryOperator接口
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