passing instance method as parameter in java 8

Question

lets say I have

public class Student {
     public Integer getGrade() { return 1;}
}

and I want to pass this function as Function in java in other class(not Student)

which syntax will allow me doing so?

Function<Student,Integer> = ***

Answer 1

Just do:

Function<Student,Integer> f = Student::getGrade;

You seem to have forgotten to put a name for the variable declaration!

Explanation:

Function<Student,Integer> represents a function that takes a Student as parameter and returns an Integer. Obviously, getGrade does not satisfy those criteria. But, since calling getGrade requires a Student object (because it's an instance method), the compiler can smartly use the Student parameter passed in to call getGrade.

If you don't understand what I mean, the syntax is equivalent to:

Function<Student,Integer> f = student -> student.getGrade();

Therefore, the below two lines are the same:

f(myStudent);
myStudent.getGrade();

Answer 2

Function<Student, Integer> means "you take a student and return any Integer value":

Function<Student, Integer> f1 = student -> 2;

If you need a student grade, then return this value from the getGrade method:

Function<Student, Integer> f2 = student -> student.getGrade();

With the method reference, it might be written in a shorter form:

Function<Student, Integer> f3 = Student::getGrade;

Answer 3

Being that getGrade isn't a static method, you'll need to first instantiate Student in order to store a reference to it.

Student student = ...;
Supplier<Integer> = student::getGrade;

You'll likely want to use a Supplier to store reference to the method because your method takes no input and returns one output (whereas a java Function takes one input and returns one output).

Answer 4

Something like this -

Function<Student, Integer> function = student -> student.getGrade();

or a method reference as

Function<Student, Integer> function = Student::getGrade;