近期看springboot的官方指南，基于java8；看到官方指南中使用较多的Stream和Lambda的功能，感觉代码精炼又简洁，给人耳目一新的感觉。
比如，如果对一个集合做遍历循环处理的话，先判断，然后对相关明细过滤或是做其它操作，如果不使用Stream和Lambda的话，代码量会比较大；
如果使用Lambda，会减少部分代码量，如果2者都使用的话，代码量进一步缩减。（注明:程序员一族，永远追求的是（懒）^$^）
摘录一些代码;
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));
集合对象roster的操作，这些代码就处理了，不需要再额外声明class和方法了。（对roster集合中的元素做age的过滤，然后输出person中的联系方式email）
下面2个类，摘自oracle官网
/*
* Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* 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
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
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;
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.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* 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
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
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;
public class Person {
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;
}
}
原文：https://www.cnblogs.com/nuli/p/12252323.html