Java8 MethodReference方法引用

package com.lgx.jdk8.part02;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.function.Function;
import java.util.function.Supplier;

/**
* 方法引用的学习
*/
public class Test02MethodReference {
public String getString(Supplier<String> supplier){
return supplier.get() + "test";
}

public String getString2(String str, Function<String, String> function){
return function.apply(str);
}

public static void main(String[] args) {
List<String> list = Arrays.asList("hello", "world", "hello world");

//之前学习Lambda的写法
list.forEach(item -> System.out.println("item = [" + item + "]"));

//方法引用的写法
list.forEach(System.out::println);

//方法引用共分为4类：
//a、类名::静态方法名
//当你使用的Lambda表达式恰好有一个静态方法可以完成，则可以使用这种方式
Student student1 = new Student("zhangsan", 60);
Student student2 = new Student("lisi", 80);
Student student3 = new Student("wangwu", 50);
Student student4 = new Student("zhaoliu", 78);

List<Student> studentList = Arrays.asList(student1, student2, student3, student4);
//studentList.sort((studentPara1, studentPara2) -> Student.compareStudentsByScore(studentPara1, studentPara2));//传统写法
/*studentList.sort(Student::compareStudentsByScore);
studentList.forEach(student -> System.out.println("student = [" + student.getScore() + "]"));

//b、引用名(对象名)::实例方法名
/*studentList.sort(new StudentComparator()::compareStudentsByScore);
studentList.forEach(student -> System.out.println("student = [" + student.getScore() + "]"));*/

//c、类名::实例方法名
//与上面那个类似，Lambda表达式传递进来的第一个参数作为当前对象，当作调用者，
//第二及以后的参数才传递给被调用的方法
/*studentList.sort(Student::compareByScore);
studentList.forEach(student -> System.out.println("student = [" + student.getScore() + "]"));
studentList.sort(Student::compareByName);
studentList.forEach(student -> System.out.println("student = [" + student.getName() + "]"));*/

//拓展下
List<String> cites = Arrays.asList("jiangxi", "hubei", "shenzhen", "beijing");
//Collections.sort(cites, (city1, city2) -> city1.compareTo(city2));//传统写法
//cites.forEach(city -> System.out.println("city = [" + city + "]"));//传统写法
Collections.sort(cites, String::compareTo);//这里是第3种写法
cites.forEach(System.out::println);//这里是第2种写法

//d、类名::new
//也叫构造方法引用
Test02MethodReference test = new Test02MethodReference();
String result = test.getString(String::new);
System.out.println("result = [" + result + "]");
String result2 = test.getString2("hello", String::new);
System.out.println("result2 = [" + result2 + "]");

}
}

class Student{
private String name;
private int score;
public Student(String name, int score) {
this.name = name;
this.score = score;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
//按照学生的成绩对学生进行排序
public static int compareStudentsByScore(Student student, Student student2){
return student.getScore() - student2.getScore();
}
//按照学生的名字对学生进行排序
public static int compareStudentsByName(Student student, Student student2){
return student.getName().compareTo(student2.getName());
}

//按照学生的成绩对学生进行排序
public int compareByScore(Student student){
return this.getScore() - student.getScore();
}
//按照学生的名字对学生进行排序
public int compareByName(Student student){
return this.getName().compareTo(student.getName());
}
}

class StudentComparator{
//按照学生的成绩对学生进行排序
public int compareStudentsByScore(Student student, Student student2){
return student.getScore() - student2.getScore();
}
//按照学生的名字对学生进行排序
public int compareStudentsByName(Student student, Student student2){
return student.getName().compareTo(student2.getName());
}
}