JAVA 8 函数式接口( java.util.function 详解)

青旅半醒 2023-01-13 10:58 87阅读 0赞

# 配合学习资料：[https://github.com/javaqzly/lambda-stream-practice.git][https_github.com_javaqzly_lambda-stream-practice.git] #

# java 8 函数式接口 #

## 简介 ##

函数式接口(Functional Interface)是Java 8对一类特殊类型的接口的称呼。 这类接口只定义了唯一的抽象方法的接口，并且这类接口使用了`@FunctionalInterface`进行注解。在jdk8中，引入了一个新的包`java.util.function`, 可以使java 8 的函数式编程变得更加简便。这个package中的接口大致分为了以下四类：

*  Function: 接收参数，并返回结果，主要方法 `R apply(T t)`
 *  Consumer: 接收参数，无返回结果, 主要方法为 `void accept(T t)`
 *  Supplier: 不接收参数，但返回结构，主要方法为 `T get()`
 *  Predicate: 接收参数，返回boolean值，主要方法为 `boolean test(T t)`

java.util.function包中所有的接口整理：

![b914d6ca0dbbb3830f9e3d8e1b46f61d.png][]

## Function ##

表示一个方法接收参数并返回结果。

### 接收单个参数 ###

<table> 
 <thead> 
  <tr> 
   <th>Interface</th> 
   <th>functional method</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Function&lt;T,R&gt;</td> 
   <td>R apply(T t)</td> 
   <td>接收参数类型为T，返回参数类型为R</td> 
  </tr> 
  <tr> 
   <td>IntFunction&lt;R&gt;</td> 
   <td>R apply(int value)</td> 
   <td>以下三个接口，指定了接收参数类型，返回参数类型为泛型R</td> 
  </tr> 
  <tr> 
   <td>LongFunction&lt;R&gt;</td> 
   <td>R apply(long value)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>Double&lt;R&gt;</td> 
   <td>R apply(double value)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>ToIntFunction&lt;T&gt;</td> 
   <td>int applyAsInt(T value)</td> 
   <td>以下三个接口，指定了返回参数类型，接收参数类型为泛型T</td> 
  </tr> 
  <tr> 
   <td>ToLongFunction&lt;T&gt;</td> 
   <td>long applyAsLong(T value)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>ToDoubleFunction&lt;T&gt;</td> 
   <td>double applyAsDouble(T value)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>IntToLongFunction</td> 
   <td>long applyAsLong(int value)</td> 
   <td>以下六个接口，既指定了接收参数类型，也指定了返回参数类型</td> 
  </tr> 
  <tr> 
   <td>IntToDoubleFunction</td> 
   <td>double applyAsLong(int value)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>LongToIntFunction</td> 
   <td>int applyAsLong(long value)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>LongToDoubleFunction</td> 
   <td>double applyAsLong(long value)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>DoubleToIntFunction</td> 
   <td>int applyAsLong(double value)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>DoubleToLongFunction</td> 
   <td>long applyAsLong(double value)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>UnaryOperator&lt;T&gt;</td> 
   <td>T apply(T t)</td> 
   <td>特殊的Function，接收参数类型和返回参数类型一样</td> 
  </tr> 
  <tr> 
   <td>IntUnaryOperator</td> 
   <td>int applyAsInt(int left, int right)</td> 
   <td>以下三个接口，指定了接收参数和返回参数类型，并且都一样</td> 
  </tr> 
  <tr> 
   <td>LongUnaryOperator</td> 
   <td>long applyAsInt(long left, long right)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>DoubleUnaryOperator</td> 
   <td>double applyAsInt(double left, double right)</td> 
   <td>&nbsp;</td> 
  </tr> 
 </tbody> 
</table>

### 接收两个参数 ###

<table> 
 <thead> 
  <tr> 
   <th>interface</th> 
   <th>functional method</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>BiFunction&lt;T,U,R&gt;</td> 
   <td>R apply(T t, U u)</td> 
   <td>接收两个参数的Function</td> 
  </tr> 
  <tr> 
   <td>ToIntBiFunction&lt;T,U&gt;</td> 
   <td>int applyAsInt(T t, U u)</td> 
   <td>以下三个接口，指定了返回参数类型，接收参数类型分别为泛型T, U</td> 
  </tr> 
  <tr> 
   <td>ToLongBiFunction&lt;T,U&gt;</td> 
   <td>long applyAsLong(T t, U u)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>ToDoubleBiFunction&lt;T,U&gt;</td> 
   <td>double appleyAsDouble(T t, U u)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>BinaryOperator&lt;T&gt;</td> 
   <td>T apply(T t, T u)</td> 
   <td>特殊的BiFunction, 接收参数和返回参数类型一样</td> 
  </tr> 
  <tr> 
   <td>IntBinaryOperator</td> 
   <td>int applyAsInt(int left, int right)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>LongBinaryOperator</td> 
   <td>long applyAsInt(long left, long right)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>DoubleBinaryOperator</td> 
   <td>double applyAsInt(double left, double right)</td> 
   <td>&nbsp;</td> 
  </tr> 
 </tbody> 
</table>

## Consumer ##

表示一个方法接收参数但不产生返回值。

### 接收一个参数 ###

<table> 
 <thead> 
  <tr> 
   <th>interface</th> 
   <th>functional method</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Consumer&lt;T&gt;</td> 
   <td>void accept(T t)</td> 
   <td>接收一个泛型参数，无返回值</td> 
  </tr> 
  <tr> 
   <td>IntConsumer</td> 
   <td>void accept(int value)</td> 
   <td>以下三个类，接收一个指定类型的参数</td> 
  </tr> 
  <tr> 
   <td>LongConsumer</td> 
   <td>void accept(long value)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>DoubleConsumer</td> 
   <td>void accept(double value)</td> 
   <td>&nbsp;</td> 
  </tr> 
 </tbody> 
</table>

### 接收两个参数 ###

<table> 
 <thead> 
  <tr> 
   <th>interface</th> 
   <th>functional method</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>BiConsumer&lt;T,U&gt;</td> 
   <td>void accept(T t, U u)</td> 
   <td>接收两个泛型参数</td> 
  </tr> 
  <tr> 
   <td>ObjIntConsumer&lt;T&gt;</td> 
   <td>void accept(T t, int value)</td> 
   <td>以下三个类，接收一个泛型参数，一个指定类型的参数</td> 
  </tr> 
  <tr> 
   <td>ObjLongConsumer&lt;T&gt;</td> 
   <td>void accept(T t, long value)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>ObjDoubleConsumer&lt;T&gt;</td> 
   <td>void accept(T t, double value)</td> 
   <td>&nbsp;</td> 
  </tr> 
 </tbody> 
</table>

## Supplier ##

返回一个结果，并不要求每次调用都返回一个新的或者独一的结果

<table> 
 <thead> 
  <tr> 
   <th>interface</th> 
   <th>functional method</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Supplier&lt;T&gt;</td> 
   <td>T get()</td> 
   <td>返回类型为泛型T</td> 
  </tr> 
  <tr> 
   <td>BooleanSupplier</td> 
   <td>boolean getAsBoolean()</td> 
   <td>以下三个接口，返回指定类型</td> 
  </tr> 
  <tr> 
   <td>IntSupplier</td> 
   <td>int getAsInt()</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>LongSupplier</td> 
   <td>long getAsLong()</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>DoubleSupplier</td> 
   <td>double getAsDouble()</td> 
   <td>&nbsp;</td> 
  </tr> 
 </tbody> 
</table>

## Predicate ##

根据接收参数进行断言，返回boolean类型

<table> 
 <thead> 
  <tr> 
   <th>interface</th> 
   <th>functional method</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Predicate&lt;T&gt;</td> 
   <td>boolean test(T t)</td> 
   <td>接收一个泛型参数</td> 
  </tr> 
  <tr> 
   <td>IntPredicate</td> 
   <td>boolean test(int value)</td> 
   <td>以下三个接口，接收指定类型的参数</td> 
  </tr> 
  <tr> 
   <td>LongPredicate</td> 
   <td>boolean test(long value)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>DoublePredicate</td> 
   <td>boolean test(double value)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td>BiPredicate&lt;T,U&gt;</td> 
   <td>boolean test(T t, U u)</td> 
   <td>接收两个泛型参数，分别为T，U</td> 
  </tr> 
 </tbody> 
</table>

[https_github.com_javaqzly_lambda-stream-practice.git]: https://github.com/javaqzly/lambda-stream-practice.git
[b914d6ca0dbbb3830f9e3d8e1b46f61d.png]: /images/20221022/478234c200594e68bb097fe13418f98b.png