【java】【java8】Lambda、Stream、Function、Consumer、Predicate、Supplier

Lambda基本概念

A lambda expression is an unnamed function with parameters and a body.(匿名函数[参数+函数体])
The lambda expression body can be a block statement or an expression.(函数体可以是表达式或者是函数语句)
-> separates the parameters and the body.（分隔符）

语法规则：
(Parameters) -> { Body } (单个参数的时候左边括号也是可以省去的，Body可以没有花括号，那就成为了表达式)

注意点：
lambda表达式主体可能有局部变量语句。我们可以在lambda表达体中使用break，continue和return。 我们甚至可以从lambda表达体中抛出异常。
lambda表达式没有名称，因为它表示匿名内部类。
lambda表达式的返回类型由编译器推断。(隐式、显式)
lambda表达式不能像一个方法一样使用throws子句。
在通用功能界面中定义了lambda表达式不能通用。

举例：
(int x) -> x + 1 takes an int parameter and returns the parameter value incremented by 1.
(int x, int y) -> x + y takes two int parameters and returns the sum.
(String msg)->{System.out.println(msg);} takes a String parameter and prints it on the standard output.
msg->System.out.println(msg) takes a parameter and prints it on the standard output. It is identical to the code above.
() -> "hi" takes no parameters and returns a string.（例如BooleanSupplier）
(String str) -> str.length() takes a String parameter and returns its length.

示例代码一：
public class Test06 {
public static void main(String[] args) {
MyIntegerCalculator myIntegerCalculator = (Integer s1) -> s1 * 2;//接口方法具体实现   //s1的参数类型Integer可以不写  隐式 可以由javac通过上下文推导
System.out.println("1- Result x2 : " + myIntegerCalculator.calcIt(5));//10
}
}

interface MyIntegerCalculator {
public Integer calcIt(Integer s1);
}

示例代码二：
public class Test06 {
public static void main(String[] argv) {
//注意参数类型
Processor stringProcessor = (String str) -> str.length();//实现接口方法
SecondProcessor secondProcessor = (String str) -> str.length();
//stringProcessor = secondProcessor; //compile error
String name = "stringProcessor";
int length = stringProcessor.getStringLength(name);
System.out.println(length);

String name2 = "secondProcessor2";
int length2 = secondProcessor.noName(name2);
System.out.println(length2);

}
}

@FunctionalInterface
interface Processor {
int getStringLength(String str);
}

@FunctionalInterface
interface SecondProcessor {
int noName(String str);
}

好处：简化代码

原来写法：为button添加按钮事件
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
System.out.println("hi");
}
});

lambda写法：
button.addActionListener(e->System.out.println("hi"))

解释：
Instead of passing in an inner class that implements an interface, we're passing in a block of code.
(不在需要匿名类去实现接口)
e is the name of a parameter,
-> separates the parameter from the body of the lambda expression.
In the lambda expression the parameter e is not declared with a type.
javac is inferring the type of e from its context, the signature of addActionListener.
(不要申明参数的类型 javac会根据上下文去自动获取相对应的类型)
We don't need to explicitly write out the type when it's obvious.
The lambda method parameters are still statically typed.

示例代码：

package Test;

import java.util.Arrays;
import java.util.List;

public class Test02 {

public static void main(String[] args) {

String[] atp = {"Rafael Nadal", "Novak Djokovic", "Stanislas Wawrinka", "David Ferrer", "Roger Federer", "Andy Murray", "Tomas Berdych", "Juan Martin Del Potro", "Richard Gasquet", "John Isner"};
List<String> players = Arrays.asList(atp);

// Old looping
for (String player : players) {
System.out.print(player + "; ");
}

System.out.println("");

/**
* default void forEach(Consumer<? super T> action) {
Objects.requireNonNull(action);
for (T t : this) {
action.accept(t);
}
}
* */

// Using lambda expression and functional operations
players.forEach((player) -> System.out.print(player + "; "));

System.out.println("");

// Using double colon operator in Java 8
players.forEach(System.out::println);

System.out.println("");

// Using anonymous innerclass  实现匿名函数类的时候 如果参数列表中有参数 那么其就应该在使用lambda的时候就加上参数
new Thread(new Runnable() {
@Override
public void run() {
System.out.println("Hello world !");
}
}).start();

// Using lambda expression
new Thread(() -> System.out.println("Hello world !")).start();

// Using anonymous innerclass
Runnable race1 = new Runnable() {
@Override
public void run() {
System.out.println("Hello world !");
}
};

// Using lambda expression
Runnable race2 = () -> System.out.println("Hello world !");

// Run em!
race1.run();
race2.run();
}

}

package Test;

import java.util.Arrays;
import java.util.Comparator;

public class Test04 {

public static void main(String[] args) {

String[] players = {"Rafael Nadal", "Novak Djokovic", "Stanislas Wawrinka", "David Ferrer", "Roger Federer", "Andy Murray", "Tomas Berdych", "Juan Martin Del Potro", "Richard Gasquet", "John Isner"};

// Show the list of players
System.out.print("Show the list of players:\n");
Arrays.asList(players).forEach((player) -> System.out.println(player));

// Sort players by name using anonymous innerclass   //Comparator是接口类型
Arrays.sort(players, new Comparator<String>() {
@Override
public int compare(String s1, String s2) {
return (s1.compareTo(s2));
}
});

// Sort players by name using lambda expression
Comparator<String> sortByName = (String s1, String s2) -> (s1.compareTo(s2));
Arrays.sort(players, sortByName);
// or this
Arrays.sort(players, (String s1, String s2) -> (s1.compareTo(s2)));

System.out.print("\nShow the list of players after sorting by name:\n");
Arrays.asList(players).forEach((player) -> System.out.println(player));

// Sort players by surname using anonymous innerclass
Arrays.sort(players, new Comparator<String>() {
@Override
public int compare(String s1, String s2) {
return (s1.substring(s1.indexOf(" ")).compareTo(s2.substring(s2.indexOf(" "))));
}
});

// Sort players by surname using lambda expression  //根据姓开始字母顺序进行排序
Comparator<String> sortBySurname = (String s1, String s2) -> (s1.substring(s1.indexOf(" ")).compareTo(s2.substring(s2.indexOf(" "))));
Arrays.sort(players, sortBySurname);
// or this
Arrays.sort(players, (String s1, String s2) -> (s1.substring(s1.indexOf(" ")).compareTo(s2.substring(s2.indexOf(" ")))));

System.out.print("\nShow the list of players after sorting by surname:\n");
Arrays.asList(players).forEach((player) -> System.out.println(player));

// Sort players by name lenght using anonymous innerclass
Arrays.sort(players, new Comparator<String>() {
@Override
public int compare(String s1, String s2) {
return (s1.length() - s2.length());
}
});

// Sort players by name lenght using lambda expression
Comparator<String> sortByNameLenght = (String s1, String s2) -> (s1.length() - s2.length());
Arrays.sort(players, sortByNameLenght);
// or this
Arrays.sort(players, (String s1, String s2) -> (s1.length() - s2.length()));

System.out.print("\nShow the list of players after sorting by length:\n");
Arrays.asList(players).forEach((player) -> System.out.println(player));

// Sort players by last letter using anonymous innerclass
Arrays.sort(players, new Comparator<String>() {
@Override
public int compare(String s1, String s2) {
return (s1.charAt(s1.length() - 1) - s2.charAt(s2.length() - 1));
}
});

// Sort players by last letter using lambda expression
Comparator<String> sortByLastLetter = (String s1, String s2) -> (s1.charAt(s1.length() - 1) - s2.charAt(s2.length() - 1));
Arrays.sort(players, sortByLastLetter);
// or this
Arrays.sort(players, (String s1, String s2) -> (s1.charAt(s1.length() - 1) - s2.charAt(s2.length() - 1)));

System.out.print("\nShow the list of players after sorting by last letter:\n");
Arrays.asList(players).forEach((player) -> System.out.println(player));
}

}

person类

package Test;

public class Person {

private String firstName, lastName, job, gender;
private int salary, age;

public Person(){}

public Person(String firstName, String lastName, String job, String gender, int age, int salary) {
this.firstName = firstName;
this.lastName = lastName;
this.gender = gender;
this.age = age;
this.job = job;
this.salary = salary;
}

public String getFirstName() {
return firstName;
}

public String getLastName() {
return lastName;
}

public String getJob() {
return job;
}

public String getGender() {
return gender;
}

public int getSalary() {
return salary;
}

public int getAge() {
return age;
}

public void setJob(String job) {
this.job = job;
}

public void setSalary(int salary) {
this.salary = salary;
}

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

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

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

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

package Test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.IntSummaryStatistics;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;
import java.util.function.Consumer;
import java.util.function.Predicate;
import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.toCollection;
import static java.util.stream.Collectors.toList;
import static java.util.stream.Collectors.toSet;

public class Test05 {

public static void main(String[] args) {
List<Person> javaProgrammers = new ArrayList<Person>() {
{
add(new Person("Elsdon", "Jaycob", "Java programmer", "male", 43, 2000));
add(new Person("Tamsen", "Brittany", "Java programmer", "female", 23, 1500));
add(new Person("Floyd", "Donny", "Java programmer", "male", 33, 1800));
add(new Person("Sindy", "Jonie", "Java programmer", "female", 32, 1600));
add(new Person("Vere", "Hervey", "Java programmer", "male", 22, 1200));
add(new Person("Maude", "Jaimie", "Java programmer", "female", 27, 1900));
add(new Person("Shawn", "Randall", "Java programmer", "male", 30, 2300));
add(new Person("Jayden", "Corrina", "Java programmer", "female", 35, 1700));
add(new Person("Palmer", "Dene", "Java programmer", "male", 33, 2000));
add(new Person("Addison", "Pam", "Java programmer", "female", 34, 1300));
}
};

List<Person> phpProgrammers = new ArrayList<Person>() {
{
add(new Person("Jarrod", "Pace", "PHP programmer", "male", 34, 1550));
add(new Person("Clarette", "Cicely", "PHP programmer", "female", 23, 1200));
add(new Person("Victor", "Channing", "PHP programmer", "male", 32, 1600));
add(new Person("Tori", "Sheryl", "PHP programmer", "female", 21, 1000));
add(new Person("Osborne", "Shad", "PHP programmer", "male", 32, 1100));
add(new Person("Rosalind", "Layla", "PHP programmer", "female", 25, 1300));
add(new Person("Fraser", "Hewie", "PHP programmer", "male", 36, 1100));
add(new Person("Quinn", "Tamara", "PHP programmer", "female", 21, 1000));
add(new Person("Alvin", "Lance", "PHP programmer", "male", 38, 1600));
add(new Person("Evonne", "Shari", "PHP programmer", "female", 40, 1800));
}
};

// forEach examples
// Print programmers name
System.out.println("Print programmers names:");
javaProgrammers.forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));
phpProgrammers.forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));

// Increase salary by 5% to programmers
System.out.println("\n\nIncrease salary by 5% to programmers:");
Consumer<Person> giveRaise = e -> e.setSalary(e.getSalary() / 100 * 5 + e.getSalary());

javaProgrammers.forEach(giveRaise);
phpProgrammers.forEach(giveRaise);
javaProgrammers.forEach((p) -> System.out.printf("%s earns now $%,d.%n", p.getFirstName(), p.getSalary()));
phpProgrammers.forEach((p) -> System.out.printf("%s earns now $%,d.%n", p.getFirstName(), p.getSalary()));

// filter examples
// Print PHP programmers that earn more than $1,400
System.out.println("\nPHP programmers that earn more than $1,400:");
phpProgrammers.stream()
.filter((p) -> (p.getSalary() > 1400))
.forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));

// Define some filters  自定义过滤器
Predicate<Person> ageFilter = (p) -> (p.getAge() > 25);
Predicate<Person> salaryFilter = (p) -> (p.getSalary() > 1400);
Predicate<Person> genderFilter = (p) -> ("female".equals(p.getGender()));

System.out.println("\n\nFemale PHP programmers that earn more than $1,400 and are older than 24 years:");
phpProgrammers.stream()
.filter(ageFilter)
.filter(salaryFilter)
.filter(genderFilter)
.forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));

// Reuse filters
System.out.println("\n\nFemale Java programmers older than 24 years:");
javaProgrammers.stream()
.filter(ageFilter)
.filter(genderFilter)
.forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));

// limit examples
System.out.println("\n\nPrint first 3 Java programmers:");
javaProgrammers.stream()
.limit(3)
.forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));

System.out.println("\n\nPrint first 3 female Java programmers:");
javaProgrammers.stream()
.filter(genderFilter)
.limit(3)
.forEach((p) -> System.out.printf("%s %s; ", p.getFirstName(), p.getLastName()));

// sorted, collect, limit, min, max examples
System.out.println("\n\nSort and print first 5 Java programmers by name:");
List<Person> sortedJavaProgrammers = javaProgrammers
.stream()
.sorted((p, p2) -> (p.getFirstName().compareTo(p2.getFirstName())))
.limit(5)
.collect(toList());

sortedJavaProgrammers.forEach((p) -> System.out.printf("%s %s; %n", p.getFirstName(), p.getLastName()));

System.out.println("\nSort and print Java programmers by salary:");
sortedJavaProgrammers = javaProgrammers
.stream()
.sorted((p, p2) -> (p.getSalary() - p2.getSalary()))
.collect(toList());

sortedJavaProgrammers.forEach((p) -> System.out.printf("%s %s; %n", p.getFirstName(), p.getLastName()));

// min is faster than sorting and choosing the first
System.out.println("\nGet the lowest Java programmer salary:");
Person pers = javaProgrammers
.stream()
.min((p1, p2) -> (p1.getSalary() - p2.getSalary()))
.get();

System.out.printf("Name: %s %s; Salary: $%,d.", pers.getFirstName(), pers.getLastName(), pers.getSalary());

System.out.println("\nGet the highest Java programmer salary:");
Person person = javaProgrammers
.stream()
.max((p, p2) -> (p.getSalary() - p2.getSalary()))
.get();

System.out.printf("Name: %s %s; Salary: $%,d.", person.getFirstName(), person.getLastName(), person.getSalary());

// map, collect examples
System.out.println("\nGet PHP programmers first name to String:");
String phpDevelopers = phpProgrammers
.stream()
.map(Person::getFirstName)
.collect(joining(" ; "));    // this can be use as a token in further operations

System.out.println(phpDevelopers);

System.out.println("\nGet Java programmers first name to Set:");
Set<String> javaDevFirstName = javaProgrammers
.stream()
.map(Person::getFirstName)
.collect(toSet());

javaDevFirstName.stream().forEach((s) -> System.out.printf("%s ", s));;

System.out.println("\nGet Java programmers last name to TreeSet:");
TreeSet<String> javaDevLastName = javaProgrammers
.stream()
.map(Person::getLastName)
.collect(toCollection(TreeSet::new));

javaDevLastName.stream().forEach((s) -> System.out.printf("%s ", s));

int numProcessorsOrCores = Runtime.getRuntime().availableProcessors();
System.out.printf("\n\nParallel version on %s-core machine:", numProcessorsOrCores);

// parrallel stream, sum examples
System.out.println("\nCalculate total money spent for paying Java programmers:");
int totalSalary = javaProgrammers
.parallelStream()
.mapToInt(p -> p.getSalary())
.sum();

System.out.printf("Money spent for paying Java programmers: $%,d %n", totalSalary);

//Get count, min, max, sum, and average for numbers
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
IntSummaryStatistics stats = numbers
.stream()
.mapToInt((x) -> x)
.summaryStatistics();

System.out.println("Highest number in List : " + stats.getMax());
System.out.println("Lowest number in List : " + stats.getMin());
System.out.println("Sum of all numbers : " + stats.getSum());
System.out.println("Average of all numbers : " + stats.getAverage());
}

}

Stream基本概念

Stream是Java 8中引入的一个新的抽象层。使用流，您可以以类似于SQL语句的声明方式来处理数据。例如，以下SQL语句

SELECT max（salary），employee_id，employee_name FROM Employee

上述SQL表达式自动返回最高受薪雇员的详细信息，而不需要客户端做任何事情。在Java中使用集合框架，开发人员必须使用循环并进行重复检查。

另一个问题是效率;由于现在的电脑基本都是多核处理器，因此Java开发人员可以编写并行代码处理，但是往往会出错

为了解决这些问题，Java 8引入了流的概念，让开发人员以声明方式处理数据，并利用多核架构，而无需为其编写任何特定的代码。

(代码简洁+多核处理)

stream并不是某种数据结构，它只是数据源的一种视图。这里的数据源可以是一个数组，Java容器或I/O channel等。正因如此要得到一个stream通常不会手动创建，而是调用对应的工具方法，比如：

调用

Collection.stream()

或者

Collection.parallelStream()

方法
调用

Arrays.stream(T[] array)

方法

常见的stream接口继承关系如图：


图中4种stream接口继承自

BaseStream

，其中

IntStream,
LongStream, DoubleStream

对应三种基本类型（

int, long, double

，注意不是包装类型），

Stream

对应所有剩余类型的stream视图。为不同数据类型设置不同stream接口，可以1.提高性能，2.增加特定接口函数。



你可能会奇怪为什么不把

IntStream

等设计成

Stream

的子接口？毕竟这接口中的方法名大部分是一样的。答案是这些方法的名字虽然相同，但是返回类型不同，如果设计成父子接口关系，这些方法将不能共存，因为Java不允许只有返回类型不同的方法重载。

虽然大部分情况下stream是容器调用

Collection.stream()

方法得到的，但stream和collections有以下不同：
无存储。stream不是一种数据结构，它只是某种数据源的一个视图，数据源可以是一个数组，Java容器或I/O channel等。
为函数式编程而生。对stream的任何修改都不会修改背后的数据源，比如对stream执行过滤操作并不会删除被过滤的元素，而是会产生一个不包含被过滤元素的新stream。(重新生成+副本)
惰式执行。stream上的操作并不会立即执行，只有等到用户真正需要结果的时候才会执行。(中间操作和结束操作)
可消费性。stream只能被“消费”一次，一旦遍历过就会失效，就像容器的迭代器那样，想要再次遍历必须重新生成。

count = strings.stream().filter(string -> string.isEmpty()).count();//filter里面是定义好的规则 其参数就是predicate
System.out.println("Empty Strings: " + count);

count = strings.stream().filter(string -> string.length() == 3).count();
System.out.println("Strings of length 3: " + count);

每次使用都是重新调用stream()

对stream的操作分为为两类，中间操作(intermediate operations)和结束操作(terminal
operations)，二者特点是：
中间操作总是会惰式执行，调用中间操作只会生成一个标记了该操作的新stream，仅此而已。
结束操作会触发实际计算，计算发生时会把所有中间操作积攒的操作以pipeline的方式执行，这样可以减少迭代次数。计算完成之后stream就会失效。下表汇总了

Stream

接口的部分常见方法：

操作类型	接口方法
中间操作	concat() distinct() filter() flatMap() limit() map() peek() skip() sorted() parallel() sequential() unordered()
结束操作	allMatch() anyMatch() collect() count() findAny() findFirst() forEach() forEachOrdered() max() min() noneMatch() reduce() toArray()

不要在结束操作后面再调用中间操作
示例代码：

package Java.Stream;

import java.util.*;
import java.util.stream.Collectors;

public class Java8Tester {
public static void main(String args[]) {
System.out.println("Using Java 7: ");

// Count empty strings
List<String> strings = Arrays.asList("abc", "", "bc", "efg", "abcd", "bbbb", "jkl");
System.out.println("List: " + strings);
long count = getCountEmptyStringUsingJava7(strings);

System.out.println("Empty Strings: " + count);
count = getCountLength3UsingJava7(strings);

System.out.println("Strings of length 3: " + count);

//Eliminate empty string
List<String> filtered = deleteEmptyStringsUsingJava7(strings);
System.out.println("Filtered List: " + filtered);

//Eliminate empty string and join using comma.
String mergedString = getMergedStringUsingJava7(strings, ", ");
System.out.println("Merged String: " + mergedString);

List<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5);
//get list of square of distinct numbers
List<Integer> squaresList = getSquares(numbers);
System.out.println("Squares List: " + squaresList);

List<Integer> integers = Arrays.asList(1, 2, 13, 4, 15, 6, 17, 8, 19);
System.out.println("List: " + integers);
System.out.println("Highest number in List : " + getMax(integers));
System.out.println("Lowest number in List : " + getMin(integers));
System.out.println("Sum of all numbers : " + getSum(integers));
System.out.println("Average of all numbers : " + getAverage(integers));
System.out.println("Random Numbers: ");

//print ten random numbers
Random random = new Random();
for (int i = 0; i < 10; i++) {
System.out.println(random.nextInt());
}

System.out.println("Using Java 8: ");
System.out.println("List: " + strings);

count = strings.stream().filter(string -> string.isEmpty()).count();//filter里面是定义好的规则 其参数就是predicate
System.out.println("Empty Strings: " + count);

count = strings.stream().filter(string -> string.length() == 3).count();
System.out.println("Strings of length 3: " + count);

/**
* Collectors are used to combine the result of processing on the elements of a stream.
* Collectors can be used to return a list or a string(list和String都是可以的)
* */
filtered = strings.stream().filter(string -> !string.isEmpty()).collect(Collectors.toList());
System.out.println("Filtered List: " + filtered);

mergedString = strings.stream().filter(string -> !string.isEmpty()).collect(Collectors.joining(", "));
System.out.println("Merged String: " + mergedString);

/**
* The map method is used to map each element to its corresponding result
* key-value(结果)
* */
squaresList = numbers.stream().map(i -> i * i).distinct().collect(Collectors.toList());
System.out.println("Squares List: " + squaresList);
System.out.println("List: " + integers);

/**
* With Java 8, statistics collectors are introduced to calculate all statistics when stream processing is being done.
* IntSummaryStatistics类中已经有最大值、最小值、数量、平均值等函数
* */
IntSummaryStatistics stats = integers.stream().mapToInt((x) -> x).summaryStatistics();

System.out.println("Highest number in List : " + stats.getMax());
System.out.println("Lowest number in List : " + stats.getMin());
System.out.println("Sum of all numbers : " + stats.getSum());
System.out.println("Average of all numbers : " + stats.getAverage());
System.out.println("Random Numbers: ");

/**
* Stream has provided a new method forEach to iterate each element of the stream.
* The following code segment shows how to print 10 random numbers using forEach.
* */

/**
* The limit method is used to reduce the size of the stream.
* */

/**
* The sorted method is used to sort the stream
* */
random.ints().limit(10).sorted().forEach(System.out::println);//返回的是10个已经排好顺序的伪随机int数
random.doubles().limit(10).forEachOrdered(System.out::println);//返回的是10个伪随机double数

/**
*
two methods to generate a Stream
stream() − Returns a sequential stream considering collection as its source.
parallelStream() − Returns a parallel Stream considering collection as its source.
* */
count = strings.parallelStream().filter(string -> string.isEmpty()).count();
System.out.println("Empty Strings: " + count);
}

//返回长度为0的字符串数量
private static int getCountEmptyStringUsingJava7(List<String> strings) {
int count = 0;
for (String string : strings) {
if (string.isEmpty()) {
count++;
}
}
return count;
}

//返回长度为3的字符串数量
private static int getCountLength3UsingJava7(List<String> strings) {
int count = 0;
for (String string : strings) {
if (string.length() == 3) {
count++;
}
}
return count;
}

//去除空字符串
private static List<String> deleteEmptyStringsUsingJava7(List<String> strings) {
List<String> filteredList = new ArrayList<String>();
for (String string : strings) {
if (!string.isEmpty()) {
filteredList.add(string);
}
}
return filteredList;
}

//加入分隔符
private static String getMergedStringUsingJava7(List<String> strings, String separator) {
StringBuilder stringBuilder = new StringBuilder();//StringBuilder不是线程安全
for (String string : strings) {
if (!string.isEmpty()) {
stringBuilder.append(string);
stringBuilder.append(separator);
}
}
String mergedString = stringBuilder.toString();
return mergedString.substring(0, mergedString.length() - 2);
}

//平方
private static List<Integer> getSquares(List<Integer> numbers) {
List<Integer> squaresList = new ArrayList<>();

for (Integer number : numbers) {
Integer square = new Integer(number.intValue() * number.intValue());

if (!squaresList.contains(square)) {
squaresList.add(square);
}
}
return squaresList;
}

//获取最大值
private static int getMax(List<Integer> numbers) {
int max = numbers.get(0);

for (int i = 1; i < numbers.size(); i++) {

Integer number = numbers.get(i);

if (number.intValue() > max) {
max = number.intValue();
}
}
return max;
}

//最小值
private static int getMin(List<Integer> numbers) {
int min = numbers.get(0);

for (int i = 1; i < numbers.size(); i++) {
Integer number = numbers.get(i);

if (number.intValue() < min) {
min = number.intValue();
}
}
return min;
}

//和
private static int getSum(List numbers) {
int sum = (int) (numbers.get(0));

for (int i = 1; i < numbers.size(); i++) {
sum += (int) numbers.get(i);
}
return sum;
}

//平均值
private static int getAverage(List<Integer> numbers) {
return getSum(numbers) / numbers.size();
}
}

Function源代码

package java.util.function;

import java.util.Objects;

/**
* Represents a function that accepts one argument and produces a result.
*
* <p>This is a functional interface whose functional method is apply(Object)
*
* @param <T> the type of the input to the function
* @param <R> the type of the result of the function
*
* @since 1.8
*/
@FunctionalInterface
public interface Function<T, R> {

/**
* Applies this function to the given argument.
*
* @param t the function argument
* @return the function result
*/
R apply(T t);

/**
* Returns a composed function that first applies the {@code before}
* function to its input, and then applies this function to the result.
* If evaluation of either function throws an exception, it is relayed to
* the caller of the composed function.
*
* @param <V> the type of input to the {@code before} function, and to the
*           composed function
* @param before the function to apply before this function is applied
* @return a composed function that first applies the {@code before}
* function and then applies this function
* @throws NullPointerException if before is null
*
* @see #andThen(Function)
*/
default <V> Function<V, R> compose(Function<? super V, ? extends T> before) {
Objects.requireNonNull(before);
return (V v) -> apply(before.apply(v));
}

/**
* Returns a composed function that first applies this function to
* its input, and then applies the {@code after} function to the result.
* If evaluation of either function throws an exception, it is relayed to
* the caller of the composed function.
*
* @param <V> the type of output of the {@code after} function, and of the
*           composed function
* @param after the function to apply after this function is applied
* @return a composed function that first applies this function and then
* applies the {@code after} function
* @throws NullPointerException if after is null
*
* @see #compose(Function)
*/
default <V> Function<T, V> andThen(Function<? super R, ? extends V> after) {
Objects.requireNonNull(after);
return (T t) -> after.apply(apply(t));
}

/**
* Returns a function that always returns its input argument.
*
* @param <T> the type of the input and output objects to the function
* @return a function that always returns its input argument
*/
static <T> Function<T, T> identity() {
return t -> t;
}
}

实例代码

package Test.FCPS;

import java.util.function.Function;

public class testFunction {
public static void main(String[] args) {
//简单的,只有一行
Function<String, String> function1 = (x) -> "test result1: " + x;

//标准的,有花括号, return, 分号.
Function<String, String> function2 = (x) -> {
return "after function1 "+" test result2: " + x;
};

Function<String, String> function3 = (x) -> {
return "before function2 "+" test result3: " + x;
};
System.out.println(function1.apply("98"));
System.out.println(function1.andThen(function2).apply("100"));//先执行function1 然后将其结果作为参数传递到function2中
System.out.println(function2.andThen(function1).apply("100"));
System.out.println(function2.compose(function3).apply("fun100"));//先执行function3 在执行function2
System.out.println(Function.identity());
}
}

/**

test result1: 98
after function1  test result2: test result1: 100
after function1  test result2: before function2  test result3: fun100
java.util.function.Function$$Lambda$6/558638686@448139f0

* */

Predicate源代码

package java.util.function;

import java.util.Objects;

/**
* Represents a predicate (boolean-valued function) of one argument.
*
* This is afunctional interface whose functional method is test(Object).
*
* @param <T> the type of the input to the predicate
*
* @since 1.8
*/
@FunctionalInterface
public interface Predicate<T> {

/**
* Evaluates this predicate on the given argument.
*
* @param t the input argument
* @return  true if the input argument matches the predicate,otherwise false
*/
boolean test(T t);

/**
* Returns a composed predicate that represents a short-circuiting logical
* AND of this predicate and another.  When evaluating the composed
* predicate, if this predicate is {@code false}, then the {@code other}
* predicate is not evaluated.
*
* <p>Any exceptions thrown during evaluation of either predicate are relayed
* to the caller; if evaluation of this predicate throws an exception, the
* {@code other} predicate will not be evaluated.
*
* @param other a predicate that will be logically-ANDed with this
*              predicate
* @return a composed predicate that represents the short-circuiting logical
* AND of this predicate and the {@code other} predicate
* @throws NullPointerException if other is null
*/
default Predicate<T> and(Predicate<? super T> other) {
Objects.requireNonNull(other);
return (t) -> test(t) && other.test(t);
}

/**
* Returns a predicate that represents the logical negation of this
* predicate.
*
* @return a predicate that represents the logical negation of this
* predicate
*/
default Predicate<T> negate() {
return (t) -> !test(t);
}

/**
* Returns a composed predicate that represents a short-circuiting logical
* OR of this predicate and another.  When evaluating the composed
* predicate, if this predicate is {@code true}, then the {@code other}
* predicate is not evaluated.
*
* <p>Any exceptions thrown during evaluation of either predicate are relayed
* to the caller; if evaluation of this predicate throws an exception, the
* {@code other} predicate will not be evaluated.
*
* @param other a predicate that will be logically-ORed with this
*              predicate
* @return a composed predicate that represents the short-circuiting logical
* OR of this predicate and the {@code other} predicate
* @throws NullPointerException if other is null
*/
default Predicate<T> or(Predicate<? super T> other) {
Objects.requireNonNull(other);
return (t) -> test(t) || other.test(t);
}

/**
* Returns a predicate that tests if two arguments are equal according
* to {@link Objects#equals(Object, Object)}.
*
* @param <T> the type of arguments to the predicate
* @param targetRef the object reference with which to compare for equality,
*               which may be {@code null}
* @return a predicate that tests if two arguments are equal according
* to {@link Objects#equals(Object, Object)}
*/
static <T> Predicate<T> isEqual(Object targetRef) {
return (null == targetRef)
? Objects::isNull
: object -> targetRef.equals(object);
}
}

实例代码

package Java.FCPS.PredicateStudy;

import java.util.function.Predicate;

public class Test01 {
public static void main(String[] args) {
Predicate<String> predicate=(s)->s.length()>5;
System.out.println(predicate.test("predicate"));
}
}

package Java.FCPS.PredicateStudy;

import java.util.*;
import java.util.function.Predicate;

class Box {
private int weight = 0;
private String color = "";

public Box() {
}

public Box(int weight, String color) {
this.weight = weight;
this.color = color;
}

public Integer getWeight() {
return weight;
}

public void setWeight(Integer weight) {
this.weight = weight;
}

public String getColor() {
return color;
}

public void setColor(String color) {
this.color = color;
}

public String toString() {
return "Apple{" + "color='" + color + '\'' + ", weight=" + weight + '}';
}
}

public class Test02 {

public static void main(String[] args) {

List<Box> inventory = Arrays.asList(new Box(80, "green"), new Box(155, "green"), new Box(120, "red"));

//filter中的参数更好像是定义了一组规则  按照这个规则  然后predicate调用test函数
List<Box> greenApples = filter(inventory, Test02::isGreenApple);
System.out.println(greenApples);

List<Box> heavyApples = filter(inventory, Test02::isHeavyApple);
System.out.println(heavyApples);

List<Box> greenApples2 = filter(inventory, (Box a) -> "green".equals(a.getColor()));
System.out.println(greenApples2);

List<Box> heavyApples2 = filter(inventory, (Box a) -> a.getWeight() > 150);
System.out.println(heavyApples2);

List<Box> weirdApples = filter(inventory, (Box a) -> a.getWeight() < 80 || "brown".equals(a.getColor()));
System.out.println(weirdApples);
}

public static boolean isGreenApple(Box apple) {
return "green".equals(apple.getColor());
}

public static boolean isHeavyApple(Box apple) {
return apple.getWeight() > 150;
}

public static List<Box> filter(List<Box> inventory,
Predicate<Box> p) {
List<Box> result = new ArrayList<>();
for (Box apple : inventory) {
if (p.test(apple)) {
result.add(apple);
}
}
return result;
}

}

package Java.FCPS.PredicateStudy;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Function;
import java.util.function.Predicate;

class Student {
public int id;
public long gpa;
public String name;

Student(int id, long g, String name) {
this.id = id;
this.gpa = g;
this.name = name;
}

@Override
public String toString() {
return id + ":" + name + ": " + gpa;
}
}

public class Test03 {
public static void main(String[] args) {
List<Student> employees = Arrays.asList(
new Student(1, 5, "John"),
new Student(2, 4, "Jane"),
new Student(3, 3, "Jack")
);

// with predicate
System.out.println(findStudents(employees, createCustomPredicateWith(4)));

// with function definition, both are same
Function<Double, Predicate<Student>> customFunction = threshold -> (e -> e.gpa > threshold);
System.out.println(findStudents(employees, customFunction.apply(4D)));
}

private static Predicate<Student> createCustomPredicateWith(double threshold) {
return e -> e.gpa >= threshold;
}

private static List<Student> findStudents(List<Student> employees, Predicate<Student> predicate) {
List<Student> result = new ArrayList<>();

for (Student e : employees) {
if (predicate.test(e)) {
result.add(e);
}
}

return result;
}

}

/**
[1:John: 5, 2:Jane: 4]
[1:John: 5]
* */

Consumer源代码

package java.util.function;

import java.util.Objects;

/**
* Represents an operation that accepts a single input argument and returns no
* result. Unlike most other functional interfaces, {@code Consumer} is expected
* to operate via side-effects.
*
* <p>This is a <a href="package-summary.html">functional interface</a>
* whose functional method is {@link #accept(Object)}.
*
* @param <T> the type of the input to the operation
*
* @since 1.8
*/
@FunctionalInterface
public interface Consumer<T> {

/**
* Performs this operation on the given argument.
*
* @param t the input argument
*/
void accept(T t);

/**
* Returns a composed {@code Consumer} that performs, in sequence, this
* operation followed by the {@code after} operation. If performing either
* operation throws an exception, it is relayed to the caller of the
* composed operation.  If performing this operation throws an exception,
* the {@code after} operation will not be performed.
*
* @param after the operation to perform after this operation
* @return a composed {@code Consumer} that performs in sequence this
* operation followed by the {@code after} operation
* @throws NullPointerException if {@code after} is null
*/
default Consumer<T> andThen(Consumer<? super T> after) {
Objects.requireNonNull(after);
return (T t) -> { accept(t); after.accept(t); };
}
}

实例代码

package Java.FCPS.ConsumerStudy;

import java.util.function.Consumer;

public class Test01 {
public static void main(String[] args) {
Consumer<String> c = (x) -> System.out.println(x.toLowerCase());
c.accept("CONSUMER");
}
}

package Java.FCPS.ConsumerStudy;

import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;
public class Test02 {

public static void main(String[] args) {
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

//使用匿名函数形式
numbers.forEach(new Consumer<Integer>() {
@Override
public void accept(Integer integer) {
System.out.println(integer);
}
});

//使用Lambda
List<Integer> numbers2 = Arrays.asList(11, 21, 31, 41, 51, 61, 71, 81, 91, 110);
Consumer<List> consumer=(x)-> System.out.println(x);
consumer.accept(numbers2);

}
}

package Java.FCPS.ConsumerStudy;

import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;

class Student {
public int id;
public double gpa;
public String name;

public Student(){}

public Student(int id, long g, String name) {
this.id = id;
this.gpa = g;
this.name = name;
}

@Override
public String toString() {
return id + ":" + name + ": " + gpa;
}
}

public class Test03 {
public static void main(String[] args) {
List<Student> students = Arrays.asList(
new Student(1, 3, "John"),
new Student(2, 4, "Jane"),
new Student(3, 3,"Jack"));

Consumer<Student> raiser = e -> {
e.gpa = e.gpa * 1.1;
};

raiseStudents(students, System.out::println);
raiseStudents(students, raiser.andThen(System.out::println));//先执行raiser 然后再去执行输出操作
}

private static void raiseStudents(List<Student> employees,
Consumer<Student> fx) {
for (Student e : employees) {
fx.accept(e);
}
}

}

Supplier实例代码

package Java.FCPS.Supplier;

import java.util.function.Supplier;

public class Test01 {
public static void main(String[] args) {
Supplier<String> supplier=()->"Supplier";//定义了输出结果 因此没有必要重写toString()
System.out.println(supplier.get());
}
}

package Java.FCPS.Supplier;

import java.util.Objects;
import java.util.function.Supplier;

class SunPower {
public SunPower() {
System.out.println("Sun Power initialized..");
}
}

public class Test02 {
public static SunPower produce(Supplier<SunPower> supp) {
return supp.get();
}

public static void main(String[] args) {
SunPower power = new SunPower();

SunPower p1 = produce(() -> power);//只会初始化一次 因此只会输出一个结果
SunPower p2 = produce(() -> power);

System.out.println("Check the same object? " + Objects.equals(p1, p2));
}
}

/**
*  Sun Power initialized..
Check the same object? true
* */

package Java.FCPS.Supplier;

import java.util.function.Supplier;

class Employee{
@Override
public String toString() {
return "A EMPLOYEE";
}
}
public class Test03 {
private static Employee employee(Supplier<Employee> supplier){
return supplier.get();  //在没有写构造函数的时候  就需要重写toString方法
}

public static void main(String[] args) {
System.out.println(employee(Employee::new));// A EMPLOYEE
}
}

package Java.FCPS.Supplier;

import java.util.function.Supplier;

class Student {
public String name;
public double gpa;

public Student(){}

public Student(String name, double g) {
this.name = name;
this.gpa = g;
}

@Override
public String toString() {
return name + ": " + gpa;
}
}

public class Test04 {
public static void main(String[] args) {
Supplier<Student> studentGenerator = Test04::employeeMaker;

for (int i = 0; i < 10; i++) {
System.out.println("#" + i + ": " + studentGenerator.get());
}
}

public static Student employeeMaker() {
return new Student("A",2);
}

}

package Java.FCPS.Supplier;

import java.util.function.BooleanSupplier;
public class Test05 {
public static void main(String[] args) {
BooleanSupplier bs = () -> true;//没有参数  但是有返回结果
System.out.println(bs.getAsBoolean());

int x = 0, y= 1;
bs = () -> x > y;
System.out.println(bs.getAsBoolean());
}
}

参考资料： http://www.java2s.com/Tutorials/Java/Java_Lambda/index.htm http://blog.csdn.net/renfufei/article/details/24600507