How to write apply function of function Interface in stream.map function?
Given an ArrayList with 5 Employee(id,name,location,salary) objects,write a program to extract the location details of each Employee and store it in an ArrayList, with the help of Function.
I want to use stream.map function for this question.
import java.util.ArrayList; import java.util.List; import java.util.function.Function; import java.util.stream.Collectors; class Employee{ int id; String name; String location; int salary; Employee(int id,String name,String location,int salary){ this.id=id; this.name=name; this.location=location; this.salary=salary; } } public class JAVA8 { public static void main(String[] args){ ArrayList<Employee> al=new ArrayList<Employee>(); Employee e=new Employee(123,"Muskan","Rajasthan",34000); Employee e1=new Employee(456,"Sonali","Maharashtra",45003); Employee e2=new Employee(789,"Khushboo","LaxmanGarh",22222); Employee e3=new Employee(012,"Minakshi","USA",22); al.add(e); al.add(e1); al.add(e2); al.add(e3); Function<Employee,String> f1=(s)->(s.location); String a; List<String> li=al.stream() .map(Employee::apply) .collect(Collectors.toList()); } } But I am getting an error at this line – .map(Employee:: apply). I want to use String s=f1.apply(employeeObject) in map. How to do that
There is not apply method in Employee class. You can use the function directly
Function<Employee,String> f1=(s)->(s.location); List<String> li=al.stream().map(f1).collect(Collectors.toList()); Or use lambda inside map()
List<String> li=al.stream().map(s->s.location).collect(Collectors.toList()); 
Employee has no apply method.
You should pass the f1 instance, which implements Function<Employee,String>, to map():
List<String> li=al.stream() .map(f1) .collect(Collectors.toList()); P.S. it would be better to use a getter instead of accessing the instance variable directly:
-
with lambda
Function<Employee,String> f1 = s -> s.getLocation(); -
with method reference
Function<Employee,String> f1 = Employee::getLocation;
Of course, you can do this without f1:
List<String> li=al.stream() .map(Employee::getLocation) .collect(Collectors.toList()); 
