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目录
1. 什么是函数式接口
函数式接口
示例
示例
2. 函数式编程
示例
3. Lambda 表达式延迟执行
应用场景
示例
4. Consumer 接口
解释说明
示例
5. BiConsumer 接口
解释说明
示例
6. Predicate 接口
解释说明
示例
练习
7. Function 接口
解释说明
示例
练习
1. 什么是函数式接口
函数式接口
A functional interface is any interface that contains only one abstract method. (A functional interface may contain one or more default methods or static methods.) Because a functional interface contains only one abstract method, you can omit the name of that method when you implement it.函数式接口是仅包含一种抽象方法的任何接口。 （一个函数式接口可能包含一个或多个默认方法或静态方法。）由于一个函数式接口仅包含一个抽象方法，因此在实现该方法时可以省略该方法的名称。
示例
public interface Hello {void sayHello ( String name );static void show (){}default void print (){}private void test (){}}
JDK8 专门为函数式接口提供了一个注解标识 @FunctionalInterface ，该注解只能使用在接口类型的定义上，表明这是一个函数式接口， 编译器在编译时就是会对该接口进行检测：接口中是否只有一个抽 象接口方法。如果有多个抽象接口方法或者一个抽象接口方法也没有，则将报编译错误
示例
@FunctionalInterfacepublic interface Hello {void sayHello ( String name );static void show (){}default void print (){}private void test (){}}
注意： 如果接口类型上没有 @FunctionalInterface 注解，但接口中只有一个抽象方法，这个接口也 是函数式接口。这与 @Override 注解一样，即使方法上面没有写，同样是属于方法重写
2. 函数式编程
函数式编程是一种编程方式，在 Java 中，简单来说就是一个变量能够存储一个函数。而能够实现这种赋值操作的只有 Lambda 表达式
示例
@FunctionalInterfacepublic interface Hello {void sayHello ( String name );static void show (){}default void print (){}// private void test(){}}package com . wq . functional ;public class HelloTest {public static void main ( String [] args ) {// Hello hello = name -> System.out.println(name);Hello hello = System . out :: println ;hello . sayHello ( "Marry" );}}
3. Lambda 表达式延迟执行
应用场景
在某种条件下才会处理数据
示例
package com . wq . lambda . lazy ;public interface MsgBuilder {String buildMsg ( String ... infos );}package com . wq . lambda . lazy ;public class PrintUtil {public static void print ( boolean valid , String msg ){if ( valid ){System . out . println ( msg );}}private static String build ( String ... infos ){StringBuilder builder = new StringBuilder ();for ( String info : infos ){builder . append ( info );}return builder . toString ();}public static void print ( boolean valid , String ... infos ){if ( valid ){// MsgBuilder builder = new MsgBuilder() {// @Override// public String buildMsg(String... infos) {// return PrintUtil.build(infos);// }// };// MsgBuilder builder = (String... arr) -> {// return PrintUtil.build(arr);// };// MsgBuilder builder = arr -> PrintUtil.build(arr);MsgBuilder builder = PrintUtil :: build ;System . out . println ( builder . buildMsg ( infos ));}}}package com . wq . lambda . lazy ;public class PrintTest {public static void main ( String [] args ) {String name = "Marry" ;String desc = " is friendly" ;//不会打印任何信息，但是此时已经完成了字符串的组装，这是属于性能上的浪费PrintUtil . print ( false , name + desc );//不会打印任何信息，但是也未构建字符串PrintUtil . print ( false , name , desc );//会打印信息时才会构建字符串PrintUtil . print ( true , name , desc );}}
4. Consumer 接口
void accept ( T t ); // 接收一个被消费的数据
解释说明
Consumer 顾名思义就是消费者的意思。可以消费一个被接收到的数据，至于如何消费，就需要看这个接口被如何实现。
示例
package com . wq . consumer ;import java . util . Arrays ;import java . util . HashSet ;import java . util . List ;import java . util . Set ;import java . util . function . Consumer ;public class ConsumerTest {public static void main ( String [] args ) {// Consumer<String> c1 = new Consumer<String>() {// @Override// public void accept(String s) {// System.out.println(s);// }// };// Consumer<String> c1 = (String s) -> {// System.out.println(s);// };// Consumer<String> c1 = s -> System.out.println(s);Consumer < String > c1 = System . out :: println ;c1 . accept ( " 这是被消费的信息 " );// Consumer<String> c2 = new Consumer<String>() {// @Override// public void accept(String s) {// System.out.println(s.charAt(0));// }// };Consumer < String > c2 = s -> System . out . println ( s . charAt ( 0 ));c2 . accept ( "This is a consumer" );Consumer < String > c3 = c1 . andThen ( c2 );c3 . accept ( " 先打印再取第一个字符 " );//将数组转换为集合List < Integer > numbers = Arrays . asList ( 1 , 2 , 3 , 4 , 5 );// numbers.forEach(new Consumer<Integer>() {// @Override// public void accept(Integer integer) {// System.out.println(integer);// }// });//// numbers.forEach(integer -> System.out.println(integer));numbers . forEach ( System . out :: println );Set < String > names = new HashSet <> ();names . add ( "admin" );names . add ( "test" );names . add ( "developer" );// names.forEach(new Consumer<String>() {// @Override// public void accept(String s) {// System.out.println(s);// }// });names . forEach ( System . out :: println );}}
5. BiConsumer 接口
void accept ( T t , U u ); // 接收两个被消费的数据
解释说明
BiConsumer 也是一个消费者，只是这个消费者可以一次性消费两个数据（一般是键值对）。至于如何消费，就需要看这个接口被如何实现。
示例
package com . wq . consumer ;import java . util . HashMap ;import java . util . Map ;import java . util . function . BiConsumer ;public class BiConsumerTest {public static void main ( String [] args ) {// BiConsumer<String,Integer> bc = new BiConsumer<String, Integer>() {// @Override// public void accept(String s, Integer integer) {// System.out.println(s + "=>" + integer);// }// };BiConsumer < String , Integer > bc = ( s , i ) -> System . out . println ( s + "=>" + i );bc . accept ( "a" , 1 );Map < String , String > counties = new HashMap <> ();counties . put ( "CN" , " 中国 " );counties . put ( "EN" , " 英国 " );counties . put ( "US" , " 美国 " );// counties.forEach(new BiConsumer<String, String>() {// @Override// public void accept(String s1, String s2) {// System.out.println(s1 + "=>" + s2);// }// });counties . forEach (( s1 , s2 ) -> System . out . println ( s1 + "=>" + s2 ));}}
6. Predicate 接口
boolean test ( T t ); // 检测是否满足条件default Predicate < T > and ( Predicate <? super T > other ); // 条件之间的逻辑与衔接default Predicate < T > negate (); // 条件取反default Predicate < T > or ( Predicate <? super T > other ); // 条件之间的逻辑或衔接
解释说明
Predicate 是条件的意思，可以检测给定数据是否满足条件，也可以与其他条件进行衔接。至于如何检测，就需要看这个接口被如何实现。
示例
import java . util . function . Predicate ;public class PredicateTest {public static void main ( String [] args ) {// Predicate<String> p1 = new Predicate<String>() {// @Override// public boolean test(String s) {// return s.contains("中国");// }// };Predicate < String > p1 = s -> s . contains ( " 中 " );boolean result1 = p1 . test ( " 中华人民共和国 " );System . out . println ( result1 );Predicate < String > p2 = s -> s . indexOf ( " 啊 " ) > 0 ;boolean result2 = p2 . test ( " 中华人民共和国 " );System . out . println ( result2 );Predicate < String > p3 = p1 . negate (); // 取反System . out . println ( p3 . test ( " 中华人民共和国 " ));Predicate < String > p4 = p1 . and ( p2 ); // 逻辑与衔接System . out . println ( p4 . test ( " 中华人民共和国 " ));Predicate < String > p5 = p1 . or ( p2 ); // 逻辑或衔接System . out . println ( p5 . test ( " 中华人民共和国 " ));}}
练习
学生有姓名、性别和年龄。现有一个集合内存储有10 名学生信息，请找出其中性别为男，年龄在 20 岁以上的学生，并在控制台进行输出
package com . wq . predicate ;public class Student {private String name ;private String sex ;private int age ;public Student ( String name , String sex , int age ) {this . name = name ;this . sex = sex ;this . age = age ;}public String getName () {return name ;}public void setName ( String name ) {this . name = name ;}public String getSex () {return sex ;}public void setSex ( String sex ) {this . sex = sex ;}public int getAge () {return age ;}public void setAge ( int age ) {this . age = age ;}@Overridepublic String toString () {return "Student{" +"name='" + name + '\'' +", sex='" + sex + '\'' +", age=" + age +'}' ;}}package com . wq . predicate ;import java . util . Arrays ;import java . util . List ;import java . util . function . Consumer ;import java . util . function . Predicate ;public class Exercise {public static void main ( String [] args ) {List < Integer > numbers = Arrays . asList ( 1 , 2 , 3 , 4 , 5 );List < Student > students = Arrays . asList (new Student ( " 管理员 1" , " 男 " , 20 ),new Student ( " 管理员 2" , " 女 " , 21 ),new Student ( " 管理员 3" , " 男 " , 22 ),new Student ( " 管理员 4" , " 女 " , 23 ),new Student ( " 管理员 5" , " 男 " , 24 ),new Student ( " 管理员 6" , " 女 " , 18 ),new Student ( " 管理员 7" , " 男 " , 16 ),new Student ( " 管理员 8" , " 女 " , 19 ),new Student ( " 管理员 9" , " 男 " , 20 ),new Student ( " 管理员 0" , " 女 " , 23 ));// Predicate<Student> p1 = new Predicate<Student>() {// @Override// public boolean test(Student student) {// return "男".equals(student.getSex());// }// };Predicate < Student > p1 = stu -> " 男 " . equals ( stu . getSex ());Predicate < Student > p2 = stu -> stu . getAge () > 20 ;Predicate < Student > p3 = p1 . and ( p2 );// students.forEach(new Consumer<Student>() {// @Override// public void accept(Student student) {// if(p3.test(student)){// System.out.println(student);// }// }// });students . forEach ( student -> {if ( p3 . test ( student )){System . out . println ( student );}});}}
7. Function 接口
R apply ( T t ); // 将一个对象转换为另一种数据类型的对象default < V > Function < T , V > andThen ( Function <? super R , ? extends V >after ); // 复合转换
解释说明
Function 是功能的意思，可以将一种数据类型的对象转换为另一种数据类型的对象，至于如何转换，就需要看这个接口被如何实现。
示例
import java . util . function . Function ;public class FunctionTest {public static void main ( String [] args ) {// Function<String,Integer> f1 = new Function<String, Integer>() {// @Override// public Integer apply(String s) {// return Integer.parseInt(s);// }// };// Function<String,Integer> f1 = s -> Integer.parseInt(s);Function < String , Integer > f1 = Integer :: parseInt ;Integer i = f1 . apply ( "123" );System . out . println ( i );// Function<Integer,Double> f2 = new Function<Integer, Double>() {// @Override// public Double apply(Integer integer) {// return integer * 10.0;// }// };Function < Integer , Double > f2 = integer -> integer * 10.0 ;System . out . println ( f2 . apply ( i ));Function < String , Double > f3 = f1 . andThen ( f2 );double d = f3 . apply ( "5" );System . out . println ( d );}}
练习
现有文本存储学生信息如下：
谢霆锋 , 男 ,37刘德华 , 男 ,52郭富城 , 男 ,46张学友 , 男 ,40
要求将学生信息从文本中读取出来并转换为学生对象，然后存储在集合中
import java . io . BufferedReader ;import java . io . FileNotFoundException ;import java . io . FileReader ;import java . io . IOException ;import java . util . ArrayList ;import java . util . List ;import java . util . function . Function ;public class Exercise {public static void main ( String [] args ) {String path = "F:/stu.txt" ;// Function<String, Student> function = new Function<String, Student>() {// @Override// public Student apply(String s) {// return new Student(s.split(","));// }// };Function < String , Student > function = s -> newStudent ( s . split ( "," ));List < Student > students = readStudent ( path , function );students . forEach ( System . out :: println );System . out . println ( "========================" );// Function<String[], Student> f = new Function<String[], Student> () {// @Override// public Student apply(String[] strings) {// return new Student(strings);// }// };// Function<String[], Student> f = strings -> new Student(strings);Function < String [], Student > f = Student :: new ;List < Student > stus = readStudent1 ( path , f );stus . forEach ( System . out :: println );}public static List < Student > readStudent1 ( String path ,Function < String [], Student > function ){List < Student > students = new ArrayList <> ();try ( FileReader reader = new FileReader ( path );BufferedReader br = new BufferedReader ( reader )) {String line ;while (( line = br . readLine ()) != null ){String [] arr = line . split ( "," );Student stu = function . apply ( arr );students . add ( stu );}} catch ( FileNotFoundException e ) {e . printStackTrace ();} catch ( IOException e ) {e . printStackTrace ();}return students ;}public static List < Student > readStudent ( String path , Function < String , Student > function ){List < Student > students = new ArrayList <> ();try ( FileReader reader = new FileReader ( path );BufferedReader br = new BufferedReader ( reader )) { String line ;while (( line = br . readLine ()) != null ){Student stu = function . apply ( line );students . add ( stu );}} catch ( FileNotFoundException e ) {e . printStackTrace ();} catch ( IOException e ) {e . printStackTrace ();}return students ;}private static class Student {private String name ;private String sex ;private int age ;public Student ( String [] arr ) {this . name = arr [ 0 ];this . sex = arr [ 1 ];this . age = Integer . parseInt ( arr [ 2 ]);}public String getName () {return name ;}public void setName ( String name ) {this . name = name ;}public String getSex () {return sex ;}public void setSex ( String sex ) {this . sex = sex ;}public int getAge () {return age ;}public void setAge ( int age ) {this . age = age ;}@Overridepublic String toString () {return "Student{" +"name='" + name + '\'' +", sex='" + sex + '\'' +", age=" + age +'}' ;}}}