Java8 Predicate

code:

package com.qhong;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import static com.qhong.EmployeePredicates.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Employee e1 = new Employee(1,23,"M","Rick","Beethovan");
        Employee e2 = new Employee(2,13,"F","Martina","Hengis");
        Employee e3 = new Employee(3,43,"M","Ricky","Martin");
        Employee e4 = new Employee(4,26,"M","Jon","Lowman");
        Employee e5 = new Employee(5,19,"F","Cristine","Maria");
        Employee e6 = new Employee(6,15,"M","David","Feezor");
        Employee e7 = new Employee(7,68,"F","Melissa","Roy");
        Employee e8 = new Employee(8,79,"M","Alex","Gussin");
        Employee e9 = new Employee(9,15,"F","Neetu","Singh");
        Employee e10 = new Employee(10,45,"M","Naveen","Jain");

        List<Employee> employees = new ArrayList<Employee>();
        employees.addAll(Arrays.asList(new Employee[]{e1,e2,e3,e4,e5,e6,e7,e8,e9,e10}));

        System.out.println(filterEmployees(employees, isAdultMale()));

        System.out.println(filterEmployees(employees, isAdultFemale()));

        System.out.println(filterEmployees(employees, isAgeMoreThan(35)));

        //Employees other than above collection of "isAgeMoreThan(35)" can be get using negate()
        System.out.println(filterEmployees(employees, isAgeMoreThan(35).negate()));
    }

}

class Employee {

    public Employee(Integer id, Integer age, String gender, String fName, String lName){
        this.id = id;
        this.age = age;
        this.gender = gender;
        this.firstName = fName;
        this.lastName = lName;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    private Integer id;
    private Integer age;
    private String gender;
    private String firstName;
    private String lastName;

    //Please generate Getter and Setters

    @Override
    public String toString() {
        return this.id.toString()+" - "+this.age.toString(); //To change body of generated methods, choose Tools | Templates.
    }
}

package com.qhong;

import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Collectors;

/**
 * Created by qhong on 2017/3/14.
 */
public class EmployeePredicates
{
    public static Predicate<Employee> isAdultMale() {
        return p -> p.getAge() > 21 && p.getGender().equalsIgnoreCase("M");
    }

    public static Predicate<Employee> isAdultFemale() {
        return p -> p.getAge() > 18 && p.getGender().equalsIgnoreCase("F");
    }

    public static Predicate<Employee> isAgeMoreThan(Integer age) {
        return p -> p.getAge() > age;
    }

    public static List<Employee> filterEmployees (List<Employee> employees, Predicate<Employee> predicate) {
        return employees.stream().filter( predicate ).collect(Collectors.<Employee>toList());
    }
}

result:

[1 - 23, 3 - 43, 4 - 26, 8 - 79, 10 - 45]
[5 - 19, 7 - 68]
[3 - 43, 7 - 68, 8 - 79, 10 - 45]
[1 - 23, 2 - 13, 4 - 26, 5 - 19, 6 - 15, 9 - 15]

http://howtodoinjava.com/java-8/how-to-use-predicate-in-java-8/