Lambda是JDK 1.8新特性，用Lambda代替匿名类，可以使代码更加间接，干练。
语法规则：(param1, param2,...) ->(return param1+param2); return可以省略
function interface（函数接口）: it contains only one abstract method.
the JDK defines several standard functional interfaces, which you can find in the package java.util.function.
lambda Expressions可以和函数接口配合使用，具体demo参考代码
eg:匿名类和lambda比较
package lambda;
import java.time.LocalDate;
import java.util.LinkedList;
import java.util.List;
/**
*
* @Description:
* @author: chenlh
* @date: 2018-07-05
*/
public class Person {
public enum Sex {
MALE, FEMALE
}
String name;
LocalDate birthday;
Sex gender;
String emailAddress;
public int getAge() {
return 20;
}
public void printPerson() {
System.out.println("printPerson");
}
/**
* @return
*/
public static List<Person> createRoster() {
List p = new LinkedList();
p.add(new Person());
p.add(new Person());
p.add(new Person());
return p;
}
/**
* @return
*/
public Sex getGender() {
return Sex.MALE;
}
/**
* @return
*/
public String getEmailAddress() {
return this.getEmailAddress();
}
}
测试类:
package lambda;
import java.util.List;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
/**
*
* @Description:匿名类和lambda测试比较
* @author: chenlh
* @date: 2018-07-05
*/
public class LambdaTest {
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));
}
}
网友评论