package com.java.design.java8.MethodReference;import com.java.design.java8.entity.Student;import org.junit.Before;import org.junit.Test;import org.junit.runner.RunWith;import org.springframework.boot.test.context.SpringBootTest;import org.springframework.test.context.junit4.SpringRunner;import java.util.Arrays;import java.util.List;import java.util.function.Supplier;/** * @author 陈杨 */@RunWith(SpringRunner.class)@SpringBootTestpublic class MethodReference {一、测试数据准备private List<Student> students;private List<String> snames;private Student studentSupplier(Supplier<Student> studentSupplier) { return studentSupplier.get();}// private StudentConstructor studentConstructor =// (id, name, sex, age, addr, salary) ->// new Student(id, name, sex, age, addr, salary);private StudentConstructor studentConstructor = Student::new;private Student studentAllArgs(Integer id, String name, String sex, Integer age, String addr, Double salary) { return studentConstructor.studentAllArgs(id, name, sex, age, addr, salary);}@Beforepublic void init() { Student kirito = new Student(1, “Kirito”, “Male”, 18, “Sword Art Online”, 999999999.0); Student Asuna = new Student(2, “Asuna”, “Female”, 17, “Sword Art Online”, 999999999.0); Student Sinon = new Student(3, “Sinon”, “Female”, 16, “Gun Gale Online”, 999999999.0); Student Yuuki = new Student(4, “Yuuki”, “Female”, 15, “Alfheim Online”, 999999999.0); Student Alice = new Student(5, “Alice”, “Female”, 14, “Alicization”, 999999999.0); students = Arrays.asList(kirito, Asuna, Sinon, Yuuki, Alice); snames = Arrays.asList(“kirito”, “Asuna”, “Sinon”, “Yuuki”, “Alice”);}二、方法引用 引入@Testpublic void testMethodReference() { // MethodReference 方法引用 List<String> Iloveyou = Arrays.asList(“Kirito”, “Love”, “Asuna”); //集合遍历 Lambda System.out.println("—————————————\n"); System.out.println(“集合遍历 Lambda”); Iloveyou.forEach(str -> System.out.println(str)); //集合遍历 MethodReference System.out.println("—————————————\n"); System.out.println(“集合遍历 MethodReference”); Iloveyou.forEach(System.out::println);三、什么是方法引用// MethodReference// 方法引用是Lambda表达式的特殊替换// 方法引用本质是一个 函数指针 Function Pointer// 这个指针指向被引用方法// eg: 方法引用System.out::println 指向System.out.println()这个函数四、方法引用的分类1、 静态方法引用// 1、 静态方法引用// 静态方法引用 类名::静态方法名// 静态方法引用 功能实现等价于 调用 类的静态方法// 静态方法引用 与 调用 无任何关系// 类名.静态方法名 –>方法调用 显示传参// 类名::静态方法名 –>方法引用 隐式传参 编译器自动推断 方法引用的表达式 函数指针 指向 被引用函数System.out.println("—————————————\n");System.out.println(" 静态方法引用 按年龄排序");students.sort(StaticStudentComparator::staticCompareStudentByAge);students.forEach(System.out::println);System.out.println("—————————————\n");System.out.println(" 静态方法引用 按姓名排序");students.sort(StaticStudentComparator::staticCompareStudentByName);students.forEach(System.out::println);2、 对象实例方法引用// 2、 对象实例方法引用// 对象实例方法引用 引用名（对象名）::实例方法名// 对象实例方法引用 功能实现等价于 调用 对象实例 所拥有的 实例方法StudentComparator studentComparator = new StudentComparator();System.out.println("—————————————\n");System.out.println(" 静态方法引用 按年龄排序");students.sort(studentComparator::compareStudentByAge);students.forEach(System.out::println);System.out.println("—————————————\n");System.out.println(" 对象实例方法引用 按姓名排序");students.sort(studentComparator::compareStudentByName);students.forEach(System.out::println);3、 类实例方法引用// 3、 类实例方法引用// 类实例方法引用 类名::实例方法名System.out.println("—————————————\n");System.out.println(" 类实例方法引用 按年龄排序");students.sort(Student::classCompareStudentByAge);students.forEach(System.out::println);System.out.println("—————————————\n");System.out.println(" 类实例方法引用 按姓名排序");students.sort(Student::classCompareStudentByName);students.forEach(System.out::println);System.out.println("—————————————\n");System.out.println(" 类实例方法引用 容易理解的 字符串排序");snames.sort(String::compareToIgnoreCase);snames.forEach(System.out::println);4、 构造方法引用// 4、 构造方法引用// 构造方法引用 类名::new// 注意： 实体类Student 事先 有定义好的 全参构造方法 与无参构造方法// 若没有构造方法 需要自行添加 否则报错// Student::new 可以根据参数不同 对构造方法进行自动识别 重载// 利用无参构造方法构造studentNoArgs对象System.out.println("—————————————\n");System.out.println(“利用无参构造方法构造studentNoArgs对象”);Student studentNoArgs = this.studentSupplier(Student::new);System.out.println(studentNoArgs);// 利用自定义全参构造方法构造student对象System.out.println("—————————————\n");System.out.println(“利用全参构造方法构造studentNoArgs对象”);Student Silica = this.studentAllArgs (6, “Silica”, “Female”, 10, “Sword Art Online”, 999999999.0);System.out.println(Silica); }}五、StaticStudentComparator类 （静态方法实例引用）import com.java.design.java8.entity.Student;import java.util.Comparator;public class StaticStudentComparator { static Comparator<Student> studentAgeComparator = (first, last) -> first.getAge() - last.getAge(); static Comparator<Student> studentNameComparator = (first, last) -> first.getName().compareToIgnoreCase(last.getName()); public static int staticCompareStudentByAge(Student first, Student last) { return studentAgeComparator.compare(first, last); } public static int staticCompareStudentByName(Student first, Student last) { return studentNameComparator.compare(first, last); }}六、StudentComparator类 （对象方法实例引用）import com.java.design.java8.entity.Student;import java.util.Comparator;public class StudentComparator { Comparator<Student> studentAgeComparator = (first, last) -> first.getAge() - last.getAge(); Comparator<Student> studentNameComparator = (first, last) -> first.getName().compareToIgnoreCase(last.getName()); public int compareStudentByAge(Student first, Student last) { return studentAgeComparator.compare(first, last); } public int compareStudentByName(Student first, Student last) { return studentNameComparator.compare(first, last); }}七、StudentConstructor @FunctionalInterface接口 （构造方法实例引用）import com.java.design.java8.entity.Student;@FunctionalInterfacepublic interface StudentConstructor { Student studentAllArgs(Integer id, String name, String sex, Integer age, String addr, Double salary);}八 、Student实体类 （类实例方法引用）@Data@AllArgsConstructor@NoArgsConstructorpublic class Student { private Integer id; private String name; private String sex; private Integer age; private String addr; private Double salary; public int classCompareStudentByAge(Student student) { return this.getAge() - student.getAge(); } public int classCompareStudentByName(Student student) { return this.getName().compareToIgnoreCase(student.getName()); }}九、 测试结果 . ____ _ __ _ _ /\ / ’ __ _ () __ __ _ \ \ \ ( ( )__ | ‘_ | ‘| | ‘ / ` | \ \ \ \ \/ )| |)| | | | | || (| | ) ) ) ) ’ || .__|| ||| |_, | / / / / =========||==============|/=//// :: Spring Boot :: (v2.1.2.RELEASE)2019-02-02 17:04:20.851 INFO 16876 — [ main] c.j.d.j.MethodReference.MethodReference : Starting MethodReference on DESKTOP-87RMBG4 with PID 16876 (started by 46250 in E:\IdeaProjects\design)2019-02-02 17:04:20.852 INFO 16876 — [ main] c.j.d.j.MethodReference.MethodReference : No active profile set, falling back to default profiles: default2019-02-02 17:04:21.422 INFO 16876 — [ main] c.j.d.j.MethodReference.MethodReference : Started MethodReference in 0.878 seconds (JVM running for 1.682)—————————————集合遍历 LambdaKiritoLoveAsuna—————————————集合遍历 MethodReferenceKiritoLoveAsuna————————————— 静态方法引用 按年龄排序Student(id=5, name=Alice, sex=Female, age=14, addr=Alicization, salary=9.99999999E8)Student(id=4, name=Yuuki, sex=Female, age=15, addr=Alfheim Online, salary=9.99999999E8)Student(id=3, name=Sinon, sex=Female, age=16, addr=Gun Gale Online, salary=9.99999999E8)Student(id=2, name=Asuna, sex=Female, age=17, addr=Sword Art Online, salary=9.99999999E8)Student(id=1, name=Kirito, sex=Male, age=18, addr=Sword Art Online, salary=9.99999999E8)————————————— 静态方法引用 按姓名排序Student(id=5, name=Alice, sex=Female, age=14, addr=Alicization, salary=9.99999999E8)Student(id=2, name=Asuna, sex=Female, age=17, addr=Sword Art Online, salary=9.99999999E8)Student(id=1, name=Kirito, sex=Male, age=18, addr=Sword Art Online, salary=9.99999999E8)Student(id=3, name=Sinon, sex=Female, age=16, addr=Gun Gale Online, salary=9.99999999E8)Student(id=4, name=Yuuki, sex=Female, age=15, addr=Alfheim Online, salary=9.99999999E8)————————————— 静态方法引用 按年龄排序Student(id=5, name=Alice, sex=Female, age=14, addr=Alicization, salary=9.99999999E8)Student(id=4, name=Yuuki, sex=Female, age=15, addr=Alfheim Online, salary=9.99999999E8)Student(id=3, name=Sinon, sex=Female, age=16, addr=Gun Gale Online, salary=9.99999999E8)Student(id=2, name=Asuna, sex=Female, age=17, addr=Sword Art Online, salary=9.99999999E8)Student(id=1, name=Kirito, sex=Male, age=18, addr=Sword Art Online, salary=9.99999999E8)————————————— 对象实例方法引用 按姓名排序Student(id=5, name=Alice, sex=Female, age=14, addr=Alicization, salary=9.99999999E8)Student(id=2, name=Asuna, sex=Female, age=17, addr=Sword Art Online, salary=9.99999999E8)Student(id=1, name=Kirito, sex=Male, age=18, addr=Sword Art Online, salary=9.99999999E8)Student(id=3, name=Sinon, sex=Female, age=16, addr=Gun Gale Online, salary=9.99999999E8)Student(id=4, name=Yuuki, sex=Female, age=15, addr=Alfheim Online, salary=9.99999999E8)————————————— 类实例方法引用 按年龄排序Student(id=5, name=Alice, sex=Female, age=14, addr=Alicization, salary=9.99999999E8)Student(id=4, name=Yuuki, sex=Female, age=15, addr=Alfheim Online, salary=9.99999999E8)Student(id=3, name=Sinon, sex=Female, age=16, addr=Gun Gale Online, salary=9.99999999E8)Student(id=2, name=Asuna, sex=Female, age=17, addr=Sword Art Online, salary=9.99999999E8)Student(id=1, name=Kirito, sex=Male, age=18, addr=Sword Art Online, salary=9.99999999E8)————————————— 类实例方法引用 按姓名排序Student(id=5, name=Alice, sex=Female, age=14, addr=Alicization, salary=9.99999999E8)Student(id=2, name=Asuna, sex=Female, age=17, addr=Sword Art Online, salary=9.99999999E8)Student(id=1, name=Kirito, sex=Male, age=18, addr=Sword Art Online, salary=9.99999999E8)Student(id=3, name=Sinon, sex=Female, age=16, addr=Gun Gale Online, salary=9.99999999E8)Student(id=4, name=Yuuki, sex=Female, age=15, addr=Alfheim Online, salary=9.99999999E8)————————————— 类实例方法引用 容易理解的 字符串排序AliceAsunakiritoSinonYuuki—————————————利用无参构造方法构造studentNoArgs对象Student(id=null, name=null, sex=null, age=null, addr=null, salary=null)—————————————利用全参构造方法构造studentNoArgs对象Student(id=6, name=Silica, sex=Female, age=10, addr=Sword Art Online, salary=9.99999999E8)
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