Search with Lambda method on object properties - Java Lambda Stream

Description

Search with Lambda method on object properties

Demo Code

import java.util.List;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.Comparator;
import java.util.function.Predicate;
import java.lang.Iterable;
import java.time.chrono.IsoChronology;
import java.util.List;
import java.util.ArrayList;
import java.time.chrono.IsoChronology;
import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
import java.time.Period;

class Person {// ww w  . j a va 2s .c o  m

    public enum Sex {
        MALE, FEMALE
    }

    String name;
    LocalDate birthday;
    Sex gender;
    String emailAddress;

    Person(String nameArg, LocalDate birthdayArg, Sex genderArg,
            String emailArg) {
        name = nameArg;
        birthday = birthdayArg;
        gender = genderArg;
        emailAddress = emailArg;
    }

    public int getAge() {
        return birthday.until(IsoChronology.INSTANCE.dateNow()).getYears();
    }

    public void printPerson() {
        System.out.println(name + ", " + this.getAge());
    }

    public Sex getGender() {
        return gender;
    }

    public String getName() {
        return name;
    }

    public String getEmailAddress() {
        return emailAddress;
    }

    public LocalDate getBirthday() {
        return birthday;
    }

    public static int compareByAge(Person a, Person b) {
        return a.birthday.compareTo(b.birthday);
    }

    public static List<Person> createRoster() {

        List<Person> roster = new ArrayList<>();
        roster.add(new Person("Fred", IsoChronology.INSTANCE.date(1980, 6,
                20), Person.Sex.MALE, "fred@example.com"));
        roster.add(new Person("Jane", IsoChronology.INSTANCE.date(1990, 7,
                15), Person.Sex.FEMALE, "jane@example.com"));
        roster.add(new Person("George", IsoChronology.INSTANCE.date(1991,
                8, 13), Person.Sex.MALE, "george@example.com"));
        roster.add(new Person("Bob", IsoChronology.INSTANCE.date(2000, 9,
                12), Person.Sex.MALE, "bob@example.com"));

        return roster;
    }

}

public class RosterTest {

    interface CheckPerson {
        boolean test(Person p);
    }

    // Approach 1: Create Methods that Search for Persons that Match One
    // Characteristic

    public static void printPersonsOlderThan(List<Person> roster, int age) {
        for (Person p : roster) {
            if (p.getAge() >= age) {
                p.printPerson();
            }
        }
    }

    // Approach 2: Create More Generalized Search Methods

    public static void printPersonsWithinAgeRange(List<Person> roster,
            int low, int high) {
        for (Person p : roster) {
            if (low <= p.getAge() && p.getAge() < high) {
                p.printPerson();
            }
        }
    }

    // Approach 3: Specify Search Criteria Code in a Local Class
    // Approach 4: Specify Search Criteria Code in an Anonymous Class
    // Approach 5: Specify Search Criteria Code with a Lambda Expression

    public static void printPersons(List<Person> roster, CheckPerson tester) {
        for (Person p : roster) {
            if (tester.test(p)) {
                p.printPerson();
            }
        }
    }

    // Approach 6: Use Standard Functional Interfaces with Lambda Expressions

    public static void printPersonsWithPredicate(List<Person> roster,
            Predicate<Person> tester) {
        for (Person p : roster) {
            if (tester.test(p)) {
                p.printPerson();
            }
        }
    }

    // Approach 7: Use Lambda Expressions Throughout Your Application

    public static void processPersons(List<Person> roster,
            Predicate<Person> tester, Consumer<Person> block) {
        for (Person p : roster) {
            if (tester.test(p)) {
                block.accept(p);
            }
        }
    }

    // Approach 7, second example

    public static void processPersonsWithFunction(List<Person> roster,
            Predicate<Person> tester, Function<Person, String> mapper,
            Consumer<String> block) {
        for (Person p : roster) {
            if (tester.test(p)) {
                String data = mapper.apply(p);
                block.accept(data);
            }
        }
    }

    // Approach 8: Use Generics More Extensively

    public static <X, Y> void processElements(Iterable<X> source,
            Predicate<X> tester, Function<X, Y> mapper, Consumer<Y> block) {
        for (X p : source) {
            if (tester.test(p)) {
                Y data = mapper.apply(p);
                block.accept(data);
            }
        }
    }

    public static void main(String... args) {

    List<Person> roster = Person.createRoster();

    for (Person p : roster) {
        p.printPerson();
    }

    // Approach 1: Create Methods that Search for Persons that Match One
    // Characteristic

    System.out.println("Persons older than 20:");
    printPersonsOlderThan(roster, 20);
    System.out.println();

    // Approach 2: Create More Generalized Search Methods

    System.out.println("Persons between the ages of 14 and 30:");
    printPersonsWithinAgeRange(roster, 14, 30);
    System.out.println();

    // Approach 3: Specify Search Criteria Code in a Local Class

    System.out.println("Persons who are eligible for Selective Service:");

    class CheckPersonEligibleForSelectiveService implements CheckPerson {
       public boolean test(Person p) {
            return p.getGender() == Person.Sex.MALE
                && p.getAge() >= 18
                && p.getAge() <= 25;
        }
    }

    printPersons(
        roster, new CheckPersonEligibleForSelectiveService());


    System.out.println();

    // Approach 4: Specify Search Criteria Code in an Anonymous Class

    System.out.println("Persons who are eligible for Selective Service " +
        "(anonymous class):");

    printPersons(
        roster,
        new CheckPerson() {
            public boolean test(Person p) {
                return p.getGender() == Person.Sex.MALE
                    && p.getAge() >= 18
                    && p.getAge() <= 25;
            }
        }
    );

    System.out.println();

    // Approach 5: Specify Search Criteria Code with a Lambda Expression

    System.out.println("Persons who are eligible for Selective Service " +
        "(lambda expression):");

    printPersons(
        roster,
        (Person p) -> p.getGender() == Person.Sex.MALE
            && p.getAge() >= 18
            && p.getAge() <= 25
    );

    System.out.println();

    // Approach 6: Use Standard Functional Interfaces with Lambda
    // Expressions

    System.out.println("Persons who are eligible for Selective Service " +
        "(with Predicate parameter):");

    printPersonsWithPredicate(
        roster,
        p -> p.getGender() == Person.Sex.MALE
            && p.getAge() >= 18
            && p.getAge() <= 25
    );

    System.out.println();

    // Approach 7: Use Lamba Expressions Throughout Your Application

    System.out.println("Persons who are eligible for Selective Service " +
        "(with Predicate and Consumer parameters):");

    processPersons(
        roster,
        p -> p.getGender() == Person.Sex.MALE
            && p.getAge() >= 18
            && p.getAge() <= 25,
        p -> p.printPerson()
    );

    System.out.println();

    // Approach 7, second example

    System.out.println("Persons who are eligible for Selective Service " +
        "(with Predicate, Function, and Consumer parameters):");

    processPersonsWithFunction(
        roster,
        p -> p.getGender() == Person.Sex.MALE
            && p.getAge() >= 18
            && p.getAge() <= 25,
        p -> p.getEmailAddress(),
        email -> System.out.println(email)
    );

    System.out.println();

    // Approach 8: Use Generics More Extensively

    System.out.println("Persons who are eligible for Selective Service " +
        "(generic version):");

    processElements(
        roster,
        p -> p.getGender() == Person.Sex.MALE
            && p.getAge() >= 18
            && p.getAge() <= 25,
        p -> p.getEmailAddress(),
        email -> System.out.println(email)
    );

    System.out.println();

    // Approach 9: Use Bulk Data Operations That Accept Lambda Expressions
    // as Parameters

    System.out.println("Persons who are eligible for Selective Service " +
        "(with bulk data operations):");

    roster
        .stream()
        .filter(
            p -> p.getGender() == Person.Sex.MALE
                && p.getAge() >= 18
                && p.getAge() <= 25)
        .map(p -> p.getEmailAddress())
        .forEach(email -> System.out.println(email));
 }
}

/*
 * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
 *
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 * modification, are permitted provided that the following conditions
 * are met:
 *
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 *     notice, this list of conditions and the following disclaimer.
 *
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 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle or the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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 */

Result

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