本篇内容介绍了“JDK1.8有什么新特性”的有关知识,在实际案例的操作过程中,不少人都会遇到这样的困境,接下来就让小编带领大家学习一下如何处理这些情况吧!希望大家仔细阅读,能够学有所成!
函数式接口(functional Interface
),有且仅有一个抽象方法的接口,但可以有多个非抽象的方法。
适用于Lambda表达式使用的接口。如创建线程:
new Thread(() -> System.out.println(Thread.currentThread().getName())).start();
其中,Lambda表达式代替了new Runnable()
,这里的Runable
接口就属于函数式接口,最直观的体现是使用了 @FunctionalInterface
注解,而且使用了一个抽象方法(有且仅有一个),如下:
package java.lang; /** * The <code>Runnable</code> interface should be implemented by any * class whose instances are intended to be executed by a thread. The * class must define a method of no arguments called <code>run</code>. * <p> * This interface is designed to provide a common protocol for objects that * wish to execute code while they are active. For example, * <code>Runnable</code> is implemented by class <code>Thread</code>. * Being active simply means that a thread has been started and has not * yet been stopped. * </p><p> * In addition, <code>Runnable</code> provides the means for a class to be * active while not subclassing <code>Thread</code>. A class that implements * <code>Runnable</code> can run without subclassing <code>Thread</code> * by instantiating a <code>Thread</code> instance and passing itself in * as the target. In most cases, the <code>Runnable</code> interface should * be used if you are only planning to override the <code>run()</code> * method and no other <code>Thread</code> methods. * This is important because classes should not be subclassed * unless the programmer intends on modifying or enhancing the fundamental * behavior of the class. * * @author Arthur van Hoff * @see java.lang.Thread * @see java.util.concurrent.Callable * @since JDK1.0 */ @FunctionalInterface public interface Runnable { /** * When an object implementing interface <code>Runnable</code> is used * to create a thread, starting the thread causes the object's * <code>run</code> method to be called in that separately executing * thread. * </p><p> * The general contract of the method <code>run</code> is that it may * take any action whatsoever. * * @see java.lang.Thread#run() */ public abstract void run(); }
>修饰符 interface 接口名 { > > public abstract 返回值类型 方法名 (可选参数列表); > >}
注:public abstract
可以省略(因为默认修饰为public abstract
)
如:
public interface MyFunctionalInterface { public abstract void method(); }
@FunctionalInterface
,是JDK1.8中新引入的一个注解,专门指代函数式接口,用于一个接口的定义上。
和@Override
注解的作用类似,@FunctionalInterface
注解可以用来检测接口是否是函数式接口。如果是函数式接口,则编译成功,否则编译失败(接口中没有抽象方法或者抽象方法的个数多余1个)。
package com.xcbeyond.study.jdk8.functional; /** * 函数式接口 * @Auther: xcbeyond * @Date: 2020/5/17 0017 0:26 */ @FunctionalInterface public interface MyFunctionalInterface { public abstract void method(); // 如果存在多个抽象方法,则编译失败,即:@FunctionalInterface飘红 // public abstract void method1(); }
函数式接口:
package com.xcbeyond.study.jdk8.functional; /** * 函数式接口 * @Auther: xcbeyond * @Date: 2020/5/17 0017 0:26 */ @FunctionalInterface public interface MyFunctionalInterface { public abstract void method(); // 如果存在多个抽象方法,则编译失败,即:@FunctionalInterface飘红 // public abstract void method1(); }
测试:
package com.xcbeyond.study.jdk8.functional; /** * 测试函数式接口 * @Auther: xcbeyond * @Date: 2020/5/17 0017 0:47 */ public class MyFunctionalInterfaceTest { public static void main(String[] args) { // 调用show方法,参数中有函数式接口MyFunctionalInterface,所以可以使用Lambda表达式,来完成接口的实现 show("hello xcbeyond!", msg -> System.out.printf(msg)); } /** * 定义一个方法,参数使用函数式接口MyFunctionalInterface * @param myFunctionalInterface */ public static void show(String message, MyFunctionalInterface myFunctionalInterface) { myFunctionalInterface.method(message); } }
函数式接口,用起来是不是更加的灵活,可以在具体调用处进行接口的实现。
函数式接口,可以很友好地支持Lambda表达式。
在JDK1.8之前已经有了大量的函数式接口,最熟悉的就是java.lang.Runnable
接口了。
JDK 1.8 之前已有的函数式接口:
java.lang.Runnable
java.util.concurrent.Callable
java.security.PrivilegedAction
java.util.Comparator
java.io.FileFilter
java.nio.file.PathMatcher
java.lang.reflect.InvocationHandler
java.beans.PropertyChangeListener
java.awt.event.ActionListener
javax.swing.event.ChangeListener
而在JDK1.8新增了java.util.function
包下的很多函数式接口,用来支持Java的函数式编程,从而丰富了Lambda表达式的使用场景。
这里主要介绍四大核心函数式接口:
java.util.function.Consumer
:消费型接口
java.util.function.Supplier
:供给型接口
java.util.function.Predicate
:断定型接口
java.util.function.Function
:函数型接口
java.util.function.Consumer
接口,是一个消费型的接口,消费数据类型由泛型决定。
package java.util.function; import java.util.Objects; /** * 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><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 */ @FunctionalInterface public interface Consumer<t> { /** * Performs this operation on the given argument. * * @param t the input argument */ void accept(T t); /** * 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 */ default Consumer<t> andThen(Consumer<!--? super T--> after) { Objects.requireNonNull(after); return (T t) -> { accept(t); after.accept(t); }; } }
Consumer
接口中的抽象方法void accept(T t)
,用于消费一个指定泛型T的数据。
举例如下:
/** * 测试void accept(T t) */ @Test public void acceptMethodTest() { acceptMethod("xcbeyond", message -> { // 完成字符串的处理,即:通过Consumer接口的accept方法进行对应数据类型(泛型)的消费 String reverse = new StringBuffer(message).reverse().toString(); System.out.printf(reverse); }); } /** * 定义一个方法,用于消费message字符串 * @param message * @param consumer */ public void acceptMethod(String message, Consumer<string> consumer) { consumer.accept(message); }
方法andThen
,可以用来将多个Consumer
接口连接到一起,完成数据消费。
/** * 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 */ default Consumer<t> andThen(Consumer<!--? super T--> after) { Objects.requireNonNull(after); return (T t) -> { accept(t); after.accept(t); }; }
举例如下:
/** * 测试Consumer<t> andThen(Consumer<!--? super T--> after) * 输出结果: * XCBEYOND * xcbeyond */ @Test public void andThenMethodTest() { andThenMethod("XCbeyond", t -> { // 转换为大小输出 System.out.println(t.toUpperCase()); }, t -> { // 转换为小写输出 System.out.println(t.toLowerCase()); }); } /** * 定义一个方法,将两个Consumer接口连接到一起,进行消费 * @param message * @param consumer1 * @param consumer2 */ public void andThenMethod(String message, Consumer<string> consumer1, Consumer<string> consumer2) { consumer1.andThen(consumer2).accept(message); }
java.util.function.Supplier
接口,是一个供给型接口,即:生产型接口。只包含一个无参方法:T get()
,用来获取一个泛型参数指定类型的数据。
package java.util.function; /** * Represents a supplier of results. * * </string></string></t></t></string></t></t></t></p><p>There is no requirement that a new or distinct result be returned each * time the supplier is invoked. * * </p><p>This is a <a href="package-summary.html">functional interface</a> * whose functional method is {@link #get()}. * * @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(); }
举例如下:
@Test public void test() { String str = getMethod(() -> "hello world!"); System.out.println(str); } public String getMethod(Supplier<string> supplier) { return supplier.get(); }
java.util.function.Predicate
接口,是一个断定型接口,用于对指定类型的数据进行判断,从而得到一个判断结果(boolean
类型的值)。
package java.util.function; import java.util.Objects; /** * Represents a predicate (boolean-valued function) of one argument. * * </string></t></t></p><p>This is a <a href="package-summary.html">functional interface</a> * whose functional method is {@link #test(Object)}. * * @param <t> the type of the input to the predicate * * @since 1.8 */ @FunctionalInterface public interface Predicate<t> { /** * Evaluates this predicate on the given argument. * * @param t the input argument * @return {@code true} if the input argument matches the predicate, * otherwise {@code false} */ boolean test(T t); /** * Returns a composed predicate that represents a short-circuiting logical * AND of this predicate and another. When evaluating the composed * predicate, if this predicate is {@code false}, then the {@code other} * predicate is not evaluated. * * </t></t></p><p>Any exceptions thrown during evaluation of either predicate are relayed * to the caller; if evaluation of this predicate throws an exception, the * {@code other} predicate will not be evaluated. * * @param other a predicate that will be logically-ANDed with this * predicate * @return a composed predicate that represents the short-circuiting logical * AND of this predicate and the {@code other} predicate * @throws NullPointerException if other is null */ default Predicate<t> and(Predicate<!--? super T--> other) { Objects.requireNonNull(other); return (t) -> test(t) && other.test(t); } /** * Returns a predicate that represents the logical negation of this * predicate. * * @return a predicate that represents the logical negation of this * predicate */ default Predicate<t> negate() { return (t) -> !test(t); } /** * Returns a composed predicate that represents a short-circuiting logical * OR of this predicate and another. When evaluating the composed * predicate, if this predicate is {@code true}, then the {@code other} * predicate is not evaluated. * * </t></t></p><p>Any exceptions thrown during evaluation of either predicate are relayed * to the caller; if evaluation of this predicate throws an exception, the * {@code other} predicate will not be evaluated. * * @param other a predicate that will be logically-ORed with this * predicate * @return a composed predicate that represents the short-circuiting logical * OR of this predicate and the {@code other} predicate * @throws NullPointerException if other is null */ default Predicate<t> or(Predicate<!--? super T--> other) { Objects.requireNonNull(other); return (t) -> test(t) || other.test(t); } /** * Returns a predicate that tests if two arguments are equal according * to {@link Objects#equals(Object, Object)}. * * @param <t> the type of arguments to the predicate * @param targetRef the object reference with which to compare for equality, * which may be {@code null} * @return a predicate that tests if two arguments are equal according * to {@link Objects#equals(Object, Object)} */ static <t> Predicate<t> isEqual(Object targetRef) { return (null == targetRef) ? Objects::isNull : object -> targetRef.equals(object); } }
抽象方法boolean test(T t)
,用于条件判断。
/** * Evaluates this predicate on the given argument. * * @param t the input argument * @return {@code true} if the input argument matches the predicate, * otherwise {@code false} */ boolean test(T t);
举例如下:
/** * 测试boolean test(T t); */ @Test public void testMethodTest() { String str = "xcbey0nd"; boolean result = testMethod(str, s -> s.equals("xcbeyond")); System.out.println(result); } /** * 定义一个方法,用于字符串的判断。 * @param str * @param predicate * @return */ public boolean testMethod(String str, Predicate predicate) { return predicate.test(str); }
方法Predicate<t> and(Predicate<!--? super T--> other)
,用于将两个Predicate
进行逻辑”与“判断。
/** * Returns a composed predicate that represents a short-circuiting logical * AND of this predicate and another. When evaluating the composed * predicate, if this predicate is {@code false}, then the {@code other} * predicate is not evaluated. * * </t></t></t></t></t></p><p>Any exceptions thrown during evaluation of either predicate are relayed * to the caller; if evaluation of this predicate throws an exception, the * {@code other} predicate will not be evaluated. * * @param other a predicate that will be logically-ANDed with this * predicate * @return a composed predicate that represents the short-circuiting logical * AND of this predicate and the {@code other} predicate * @throws NullPointerException if other is null */ default Predicate<t> and(Predicate<!--? super T--> other) { Objects.requireNonNull(other); return (t) -> test(t) && other.test(t); }
方法Predicate<t> negate()
,用于取反判断。
/** * Returns a predicate that represents the logical negation of this * predicate. * * @return a predicate that represents the logical negation of this * predicate */ default Predicate<t> negate() { return (t) -> !test(t); }
方法Predicate<t> or(Predicate<!--? super T--> other)
,用于两个Predicate的逻辑”或“判断。
/** * Returns a composed predicate that represents a short-circuiting logical * OR of this predicate and another. When evaluating the composed * predicate, if this predicate is {@code true}, then the {@code other} * predicate is not evaluated. * * </t></t></t></t></p><p>Any exceptions thrown during evaluation of either predicate are relayed * to the caller; if evaluation of this predicate throws an exception, the * {@code other} predicate will not be evaluated. * * @param other a predicate that will be logically-ORed with this * predicate * @return a composed predicate that represents the short-circuiting logical * OR of this predicate and the {@code other} predicate * @throws NullPointerException if other is null */ default Predicate<t> or(Predicate<!--? super T--> other) { Objects.requireNonNull(other); return (t) -> test(t) || other.test(t); }
java.util.function.Function
接口,是一个函数型接口,用来根据一个类型的数据得到另外一个类型的数据。
package java.util.function; import java.util.Objects; /** * Represents a function that accepts one argument and produces a result. * * </t></p><p>This is a <a href="package-summary.html">functional interface</a> * whose functional method is {@link #apply(Object)}. * * @param <t> the type of the input to the function * @param <r> the type of the result of the function * * @since 1.8 */ @FunctionalInterface public interface Function<t, r> { /** * Applies this function to the given argument. * * @param t the function argument * @return the function result */ R apply(T t); /** * Returns a composed function that first applies the {@code before} * function to its input, and then applies this function to the result. * If evaluation of either function throws an exception, it is relayed to * the caller of the composed function. * * @param <v> the type of input to the {@code before} function, and to the * composed function * @param before the function to apply before this function is applied * @return a composed function that first applies the {@code before} * function and then applies this function * @throws NullPointerException if before is null * * @see #andThen(Function) */ default <v> Function<v, r> compose(Function<!--? super V, ? extends T--> before) { Objects.requireNonNull(before); return (V v) -> apply(before.apply(v)); } /** * Returns a composed function that first applies this function to * its input, and then applies the {@code after} function to the result. * If evaluation of either function throws an exception, it is relayed to * the caller of the composed function. * * @param <v> the type of output of the {@code after} function, and of the * composed function * @param after the function to apply after this function is applied * @return a composed function that first applies this function and then * applies the {@code after} function * @throws NullPointerException if after is null * * @see #compose(Function) */ default <v> Function<t, v> andThen(Function<!--? super R, ? extends V--> after) { Objects.requireNonNull(after); return (T t) -> after.apply(apply(t)); } /** * Returns a function that always returns its input argument. * * @param <t> the type of the input and output objects to the function * @return a function that always returns its input argument */ static <t> Function<t, t> identity() { return t -> t; } }
抽象方法R apply(T t)
,根据类型T的参数获取类型R的结果。
/** * Applies this function to the given argument. * * @param t the function argument * @return the function result */ R apply(T t);
举例如下:
/** * 测试R apply(T t),完成字符串整数的转换 */ @Test public void applyMethodTest() { // 字符串类型的整数 String numStr = "123456"; Integer num = applyMethod(numStr, n -> Integer.parseInt(n)); System.out.println(num); } public Integer applyMethod(String str, Function<string, integer> function) { return function.apply(str); }
方法<v> Function<v, r> compose(Function<!--? super V, ? extends T--> before)
,获取apply
的function
。
/** * Returns a composed function that first applies the {@code before} * function to its input, and then applies this function to the result. * If evaluation of either function throws an exception, it is relayed to * the caller of the composed function. * * @param <v> the type of input to the {@code before} function, and to the * composed function * @param before the function to apply before this function is applied * @return a composed function that first applies the {@code before} * function and then applies this function * @throws NullPointerException if before is null * * @see #andThen(Function) */ default <v> Function<v, r> compose(Function<!--? super V, ? extends T--> before) { Objects.requireNonNull(before); return (V v) -> apply(before.apply(v)); }
方法<v> Function<t, v> andThen(Function<!--? super R, ? extends V--> after)
,用来进行组合操作,即:”先做什么,再做什么“的场景。
/** * Returns a composed function that first applies this function to * its input, and then applies the {@code after} function to the result. * If evaluation of either function throws an exception, it is relayed to * the caller of the composed function. * * @param <v> the type of output of the {@code after} function, and of the * composed function * @param after the function to apply after this function is applied * @return a composed function that first applies this function and then * applies the {@code after} function * @throws NullPointerException if after is null * * @see #compose(Function) */ default <v> Function<t, v> andThen(Function<!--? super R, ? extends V--> after) { Objects.requireNonNull(after); return (T t) -> after.apply(apply(t)); }
函数式编程并不是Java提出的新概念,它将计算机运算看作是函数的计算。函数式编程最重要的基础是λ演算,而且λ演算的函数是可以接受函数当作输入(参数)和输出(返回值)的。
和指令式编程相比,函数式编程强调函数的计算比指令的执行重要。
和过程化编程相比,函数式编程里函数的计算可随时调用。
当然,Java大家都知道是面向对象的编程语言,一切都是基于对象的特性(抽象、封装、继承、多态)。在JDK1.8出现之前,我们关注的往往是某一对象应该具有什么样的属性,当然这也就是面向对象的核心——对数据进行抽象。但JDK1.8出现以后,这一点开始出现变化,似乎在某种场景下,更加关注某一类共有的行为(有点类似接口),这也就是JDK1.8提出函数式编程的目的。如下图所示,展示了面向对象编程到函数式编程的变化。
Lambda表达式就是更好的体现了函数式编程,而为了支持Lambda表达式,才有了函数式接口。
另外,为了在面对大型数据集合时,为了能够更加高效的开发,编写的代码更加易于维护,更加容易运行在多核CPU上,java在语言层面增加了Lambda表达式。在上一节中,我们已经知道Lambda表达式是多么的好用了 。
在JDK1.8中,函数式编程随处可见,在你使用过程中简直很爽,例如:Stream流。
函数式编程的优点,也很多,如下:
函数式编程大量使用函数,减少了代码的重复,因此程序比较短,开发速度较快。
函数式编程的自由度很高,可以写出很接近自然语言的代码。
例如,两数只差,可以写成(x, y) -> x – y
函数式编程不依赖、也不会改变外界的状态,只要给定输入参数,返回的结果必定相同。因此,每一个函数都可以被看做独立单元,很有利于进行单元测试(unit testing)和除错(debugging),以及模块化组合。
函数式编程不需要考虑"死锁",因为它不修改变量,所以根本不存在"锁"线程的问题。不必担心一个线程的数据,被另一个线程修改,所以可以很放心地把工作分摊到多个线程,部署"并发编程"。
函数式编程没有副作用,只要保证接口不变,内部实现是外部无关的。所以,可以在运行状态下直接升级代码,不需要重启,也不需要停机。
在JDK1.8中,函数式接口/编程将会随处可见,也有有助于你更好的理解JDK1.8中的一些新特性。关于函数式接口,在接下来具体特性、用法中将会体现的淋漓尽致。
JDK1.8提出的函数式接口,你是否赞同呢?
“JDK1.8有什么新特性”的内容就介绍到这里了,感谢大家的阅读。如果想了解更多行业相关的知识可以关注亿速云网站,小编将为大家输出更多高质量的实用文章!
免责声明:本站发布的内容(图片、视频和文字)以原创、转载和分享为主,文章观点不代表本网站立场,如果涉及侵权请联系站长邮箱:is@yisu.com进行举报,并提供相关证据,一经查实,将立刻删除涉嫌侵权内容。