Java8中 lambda表达式

1.用lambda表达式实现map

List cost = Arrays.asList(10.0,20.0,30.0);

cost.stream().forEach(x-> System.out.println(x));

System.out.println("----------");

cost.stream().map(x -> x + x*0.05).forEach(x -> System.out.println(x));

2. 用lambda表达式对集合进行迭代

List languages = Arrays.asList("java","scala","python");

//before java8

for(String each:languages) {

System.out.println(each);

}

System.out.println("-------");

//after java8

languages.forEach(x -> System.out.println(x));

languages.forEach(System.out::println);

3.用lambda表达式实现map与reduce

//map+reduce+lambda表达式

List cost = Arrays.asList(10.0, 20.0,30.0);

 double allCost = cost.stream().map(x -> x+x*0.05).reduce((sum,x) -> sum + x).get();

System.out.println(allCost);//63.0

等同于：

List cost = Arrays.asList(10.0, 20.0,30.0);

        double sum = 0;

        for(double each:cost) {

            each += each * 0.05;

            sum += each;

        }

        System.out.println(sum);//63.0

4.filter操作

List cost = Arrays.asList(10.0,20.0,30.0,40.0);

List filteredCost = cost.stream().filter(x -> x >25.0).collect(Collectors.toList());

filteredCost.forEach(x -> System.out.println(x));//30.0  40.0

5.与函数式接口Predicate配合

public static void filterTest(List languages, Predicate condition) {

   languages.stream().filter(x -> condition.test(x)).forEach(x -> System.out.println(x + " "));   

 }

public static void main(String[] args) {

List languages = Arrays.asList("Java","Python","scala","Shell","R");             System.out.println("Language starts with J: ");        

filterTest(languages,x -> x.startsWith("J"));        

System.out.println("\nLanguage ends with a: ");        

filterTest(languages,x -> x.endsWith("a"));        

System.out.println("\nAll languages: ");        

filterTest(languages,x -> true);        

System.out.println("\nNo languages: ");       

 filterTest(languages,x -> false);        

System.out.println("\nLanguage length bigger three: ");        

filterTest(languages,x -> x.length() > 4);   

 }

返回结果：

Language starts with J:

Java

Language ends with a:

Java

scala

All languages:

Java

Python

scala

Shell

R

No languages:

Language length bigger three:

Python

scala

Shell

6.替代匿名内部类

new Thread(new Runnable() {

            @Override            public void run() {

                System.out.println("The old runable now is using!");

            }

        }).start();

等同于

new Thread(() -> System.out.println("It's a lambda function!")).start();