4.method reference

Posted 2020-09-19

There is 4 method of the referenced method:

Student class:

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 student1, Student student2) {
        return student1.getScore() - student2.getScore();
    }

    public static int compareStudentByName(Student student1, Student student2) {
        return student1.getName().compareToIgnoreCase(student2.getName());
    }

    public int compareByScore(Student student) {
        return this.getScore() - student.getScore();
    }

    public int compareByName(Student student) {
        return this.getName().compareToIgnoreCase(student.getName());
    }
}

StudentComparator class:

public class StudentComparator {

    public int compareStudentByScore(Student student1, Student student2) {
        return student1.getScore() - student2.getScore();
    }

    public int compareStudentByName(Student student1, Student student2) {
        return student1.getName().compareToIgnoreCase(student2.getName());
    }
}

 

Test:public class MethodReferenceTest {

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) {
        Student student1 = new Student("zhangsan", 10);
        Student student2 = new Student("lisi", 90);
        Student student3 = new Student("wangwu", 50);
        Student student4 = new Student("zhaoliu", 40);

        List<Student> students = Arrays.asList(student1, student2, student3, student4);

　　　　　　 /**
　　　　　　　*　traditional invoke method
　　　　　　　*/

//        students.sort((studentParam1, studentParam2) ->
//                Student.compareStudentByScore(studentParam1, studentParam2));
//        students.forEach(student -> System.out.println(student.getScore()));

//        System.out.println("-------");
　　　　　　

　　　　　　/**
　　　　　　　*　Class::staticmethod invoke method
　　　　　　　*/

//        students.sort(Student::compareStudentByScore);
//        students.forEach(student -> System.out.println(student.getScore()));

//        students.sort((studentParam1, studentParam2) ->
//                Student.compareStudentByName(studentParam1, studentParam2));
//        students.forEach(student -> System.out.println(student.getName()));

　　　　　　　　　　　
　　　　　　/**
　　　　　　　*　Class::instancemethod invoke method
　　　　　　　*/

//        students.sort(Student::compareStudentByName);
//        students.forEach(student -> System.out.println(student.getName()));

//        StudentComparator studentComparator = new StudentComparator();

//        students.sort((studentParam1, studentParam2) ->
//                studentComparator.compareStudentByScore(studentParam1, studentParam2));
//        students.forEach(student -> System.out.println(student.getScore()));

　　　　　　/**
　　　　　　　*　instance::instancemethod invoke method
　　　　　　　*/

//        students.sort(studentComparator::compareStudentByScore);
//        students.forEach(student -> System.out.println(student.getScore()));

//        students.sort((studentParam1, studentParam2) ->
//                studentComparator.compareStudentByName(studentParam1, studentParam2));
//        students.forEach(student -> System.out.println(student.getName()));

//        students.sort(studentComparator::compareStudentByName);
//        students.forEach(student -> System.out.println(student.getName()));

//        students.sort(Student::compareByScore);
//        students.forEach(student -> System.out.println(student.getScore()));

//        students.sort(Student::compareByName);
//        students.forEach(student -> System.out.println(student.getName()));


//        List<String> cities = Arrays.asList("qingdao", "chongqing", "tianjin", "beijing");

//        Collections.sort(cities, (city1, city2) -> city1.compareToIgnoreCase(city2));
//        cities.forEach(city -> System.out.println(city));

　　　　　　/**
　　　　　　　*　Class::new invoke method
　　　　　　　*/　　　　　　

//        Collections.sort(cities, String::compareToIgnoreCase);
//        cities.forEach(System.out::println);

        MethodReferenceTest methodReferenceTest = new MethodReferenceTest();
        System.out.println(methodReferenceTest.getString(String::new));
        System.out.println(methodReferenceTest.getString2("hello", String::new));

    }
}