在java8中提供了方法引用的方式,简化了lambda表达式写法,方法引用本质上是lambda表达式的语法糖 并没有提供新的功能和特性,写法为两个冒号 "::"
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.function.BiFunction;
public class MethodReferenceTest {
public static void main(String[] args) {
MethodReferenceTest test = new MethodReferenceTest();
Student s1 = new Student("zhangsna",90);
Student s2 = new Student("wang",50);
Student s3 = new Student("zhaosl",79);
List<Student> list = Arrays.asList(s1,s2,s3);
//集合排序lambda表达式 写法
list.sort((o1,o2) -> {
return Student.compareStudentByScore(o1, o2);
});
list.sort((o1,o2) -> Student.compareStudentByScore(o1, o2));
//方法引用本质上是lambda表达式的语法糖 并没有提供新的功能和特性
//方法引用第一种模式 类名::静态方法
//相当于(o1,o2) -> Student.compareStudentByScore(o1, o2),参数按顺序传入方法 再方法引用时省略了声明参数的过程
list.sort(Student::compareStudentByScore);
//二、 引用名(对象名)::实例方法名
//以下等价 参数按顺序传入方法 再方法引用时省略了声明参数的过程
StudentComparator sc = new StudentComparator();
list.sort((o1,o2) -> sc.compareScope(o1, o2));
list.sort(sc::compareScope);
//三 类名::实例方法名
//以下等价 第一个元素调用方法第二个元素为方法的入参
list.sort((o1,o2) -> o1.compareByScore(o2));
list.sort(Student::compareByScore);
//eg
List<String> cities = Arrays.asList("qingdao","dalain","chongqing","beijing");
Collections.sort(cities, (o1,o2) -> o1.compareToIgnoreCase(o2));
Collections.sort(cities, String::compareToIgnoreCase);
cities.forEach(System.out::println);
//四 构造方法引用 类名::new
//以下等价 调用构造函数参数依次传入
Student student1 = test.initStudent("lishid", 50, (a1 ,a2) -> new Student(a1 ,a2));
Student student2 = test.initStudent("lishid", 50, Student::new);
System.out.println(student2.getName() + " " +student2.getScore());
list.forEach(v -> System.out.println(v.getScore()));
list.forEach(System.out::println);
}
public Student initStudent(String name,Integer score,BiFunction<String,Integer,Student> function) {
return function.apply(name, score);
}
}
public 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;
}
public static int compareStudentByScore(Student s1, Student s2) {
return s1.getScore() - s2.getScore();
}
public static int compareStudentByName(Student s1, Student s2) {
return s1.getName().compareToIgnoreCase(s2.getName());
}
public int compareByScore(Student student) {
return this.score - student.getScore();
}
public int compareByName(Student student) {
return this.name.compareToIgnoreCase(student.getName());
}
public String toString() {
return name + " "+ score;
}
}
public class StudentComparator {
public int compareScope(Student s1, Student s2) {
return s1.getScore() - s2.getScore();
}
public int compareByName(Student s1, Student s2) {
return s1.getName().compareToIgnoreCase(s2.getName());
}
}