Johny Kumar : How to Use Function Functional Interface in Java

Function Functional Interface :- Function Functional Interface define one abstract method named apply.

public interface Function<T,R>{

public R apply(T object);

}

Function Functional Interface apply method takes an object of T type argument and map it to another object of R type then return R type object .

Function Functional Interface Application

FunctionFunctionalInterface.java

package in.jk.java8.function;

import java.util.List;

import java.util.function.Function;

import in.jk.java8.Employee;

public class FunctionFunctionalInterface {

public static void main(String[] args) {

System.out.println("Function Functional Interface Application ...");

List<Employee> employeeList = Employee.getEmployeeList();

System.out.println("\n------- Use of Function ----------\n");

Function<Employee, EmployeeRequest> function = (employee) -> {

EmployeeRequest employeeRequest = new EmployeeRequest();

employeeRequest.setEmpId(employee.getEmpId());

employeeRequest.setName(employee.getName());

employeeRequest.setSalary(employee.getSalary());

employeeRequest.setCompany(employee.getCompany());

return employeeRequest;

};

employeeList.forEach(employee -> {

EmployeeRequest employeeRequest = function.apply(employee);

System.out.println(employeeRequest);

});

System.out.println("\n------- Function Implementation by Class ----------\n");

Function<Employee, EmployeeRequest> function1 = new EmployeeConvertor();

employeeList.forEach(employee -> {

EmployeeRequest employeeRequest = function1.apply(employee);

System.out.println(employeeRequest);

});

System.out.println(" \n Composing of Function ");

// Composing of Function

Function<Integer, Integer> addFunction = x -> x + 1;

Function<Integer, Integer> multiplyFunction = x -> x * 2;

// Composing of andThen Function

Function<Integer, Integer> addAndMultiplyFunction=null;

addAndMultiplyFunction = addFunction.andThen(multiplyFunction);

int result = addAndMultiplyFunction.apply(1);

System.out.println("Composing Result by andThen :: " + result);

// Composing of compose Function

Function<Integer, Integer> addAndMultiplyComposeFunction=null;

addAndMultiplyComposeFunction = addFunction.compose(multiplyFunction);

int result1 = addAndMultiplyComposeFunction.apply(1);

System.out.println("Composing Result by compose :: " + result1);

}

EmployeeConvertor.java

package in.jk.java8.function;

import java.util.function.Function;

import in.jk.java8.Employee;

public class EmployeeConvertor implements Function<Employee, EmployeeRequest> {

@Override

public EmployeeRequest apply(Employee employee) {

EmployeeRequest employeeRequest = new EmployeeRequest();

employeeRequest.setEmpId(employee.getEmpId());

employeeRequest.setName(employee.getName());

employeeRequest.setSalary(employee.getSalary());

employeeRequest.setCompany(employee.getCompany());

return employeeRequest;

}

EmployeeRequest.java

package in.jk.java8.function;

public class EmployeeRequest {

private int empId;

private String name;

private String company;

private int salary;

//Getters and Setters

@Override

public String toString() {

return "EmployeeRequest [empId=" + empId + ", name=" + name + ", company=" + company + ", salary=" + salary

+ "]";

}

Employee.java

package in.jk.java8;

import java.util.ArrayList;

import java.util.List;

public class Employee {

private int empId;

private String name;

private String company;

private int salary;

//Getters and Setters

@Override

public String toString() {

return "Employee [empId=" + empId + ", name=" + name + ", company=" + company + ", salary=" + salary + "]";

}

public static List<Employee>getEmployeeList() {

List<Employee> empList =new ArrayList<Employee>();

Employee employee = new Employee();

employee.setEmpId(1);

employee.setName("J K");

employee.setCompany("Google");

employee.setSalary(1000);

Employee employee1 = new Employee();

employee1.setEmpId(2);

employee1.setName("J K");

employee1.setCompany("Google");

employee1.setSalary(2000);

Employee employee2 = new Employee();

employee2.setEmpId(3);

employee2.setName("J K");

employee2.setCompany("Google");

employee2.setSalary(3000);

Employee employee3 = new Employee();

employee3.setEmpId(4);

employee3.setName("SHA");

employee3.setCompany("APAR");

employee3.setSalary(4000);

Employee employee4 = new Employee();

employee4.setEmpId(5);

employee4.setName("HM");

employee4.setCompany("PAYTM");

employee4.setSalary(5000);

Employee employee5 = new Employee();

employee5.setEmpId(5);

employee5.setName("HM");

employee5.setCompany("APAR");

employee5.setSalary(6000);

Employee employee6 = new Employee();

employee6.setEmpId(6);

employee6.setName("JK");

employee6.setCompany("APAR");

employee6.setSalary(7000);

Employee employee7 = new Employee();

employee7.setEmpId(7);

employee7.setName("JK");

employee7.setCompany("JET BRAINS");

employee7.setSalary(8000);

Employee employee8 = new Employee();

employee8.setEmpId(8);

employee8.setName("AJ");

employee8.setCompany("APAR");

employee8.setSalary(9000);

Employee employee9 = new Employee();

employee9.setEmpId(8);

employee9.setName("AJ");

employee9.setCompany("ADOBE");

employee9.setSalary(10000);

empList.add(employee);

empList.add(employee1);

empList.add(employee2);

empList.add(employee3);

empList.add(employee4);

empList.add(employee5);

empList.add(employee6);

empList.add(employee7);

empList.add(employee8);

empList.add(employee9);

return empList;

}

Output in Console ...

Function Functional Interface Application ...

------- Use of Function ----------

EmployeeRequest [empId=1, name=J K, company=Google, salary=1000]

EmployeeRequest [empId=2, name=J K, company=Google, salary=2000]

EmployeeRequest [empId=3, name=J K, company=Google, salary=3000]

EmployeeRequest [empId=4, name=SHA, company=APAR, salary=4000]

EmployeeRequest [empId=5, name=HM, company=PAYTM, salary=5000]

EmployeeRequest [empId=5, name=HM, company=APAR, salary=6000]

EmployeeRequest [empId=6, name=JK, company=APAR, salary=7000]

EmployeeRequest [empId=7, name=JK, company=JET BRAINS, salary=8000]

EmployeeRequest [empId=8, name=AJ, company=APAR, salary=9000]

EmployeeRequest [empId=8, name=AJ, company=ADOBE, salary=10000]

------- Function Implementation by Class ----------