【Java8】Lambda 表达式

面向对象编程是对数据进行抽象；函数式编程是对行为进行抽象。

Lambda 特点

面向对象编程是对数据进行抽象；函数式编程是对行为进行抽象。 核心思想: 使用不可变值和函数，函数对一个值进行处理，映射成另一个值。

1. 内部可以使用静态、非静态和局部变量
2. 在Java中又称为闭包或匿名函数
3. 有个限制，那就是只能引用 final 或 final 局部变量

Lambda 使用以及 Stream 下的接口

stream & parallelStream

parallelStream其实就是一个并行执行的流，它通过默认的ForkJoinPool，可能提高你的多线程任务的速度。

stream中常用方法

1. stream(), parallelStream()
2. filter()
3. findFirst()
4. sorted()
5. forEach()
6. map(), reduce()
7. flatMap()
8. collect(Collectors.toList())
9. distinct(),limit()
10. count()
11. min(), max()

示例

findFirst()

List<User> userList = Arrays.asList(new User("zhangsan","张三","123456","男","123@qq.com","")
                ,new User("zhangsan1","张三","123456","女","123@qq.com",""));

        Optional<User> first = userList.stream().filter(user ->
                StringUtils.endsWithIgnoreCase("张三", user.getUserName())).findFirst();
        System.out.println(first);

输出：

Optional[User[id=null, loginName='zhangsan', userName='张三', password='123456', sex='男', email='123@qq.com', address='']]

sorted()

按照年龄排序

        List<User> userList = Arrays.asList(new User("zhangsan", "张三", "123456", "男", "123@qq.com", "", 23)
                , new User("zhangsan1", "张三", "123456", "女", "123@qq.com", "", 19));
        List<User> collect = userList.stream().sorted(Comparator.comparing(User::getAge)).collect(Collectors.toList());
        System.out.println(collect);

输出：

[User[id=null, loginName='zhangsan1', userName='张三', password='123456', sex='女', email='123@qq.com', address='', age=19], User[id=null, loginName='zhangsan', userName='张三', password='123456', sex='男', email='123@qq.com', address='', age=23]]

distinct()

List<User> userList = Arrays.asList(new User("zhangsan", "张三", "123456", "男", "123@qq.com", "", 23)
                , new User("zhangsan1", "张三", "123456", "女", "123@qq.com", "", 19));
        List<String> collect = userList.stream().map(User::getLoginName).distinct().collect(Collectors.toList());
        System.out.println(collect);

输出：

[zhangsan, zhangsan1]

count()

List<User> userList = Arrays.asList(new User("zhangsan", "张三", "123456", "男", "123@qq.com", "", 23)
                , new User("zhangsan1", "张三", "123456", "女", "123@qq.com", "", 19));
        long count = userList.stream().filter(user -> user.getAge() > 19).count();
        System.out.println(count);

输出：

1

macth

anyMatch

        List<User> userList = Arrays.asList(new User("zhangsan", "张三", "123456", "男", "123@qq.com", "", 23)
                , new User("zhangsan1", "张三", "123456", "女", "123@qq.com", "", 19));
        boolean b = userList.stream().anyMatch(user -> user.getAge() == 19);
        System.out.println(b);

输出：

true

allmatch

List<User> userList = Arrays.asList(new User("zhangsan", "张三", "123456", "男", "123@qq.com", "", 23)
                , new User("zhangsan1", "张三", "123456", "女", "123@qq.com", "", 19));
        boolean b = userList.stream().allMatch(user -> user.getAge() == 19);
        System.out.println(b);

输出：

false

四大内置函数接口

消费型接口

Consumer< T> void accept(T t)有参数，无返回值的抽象方法；

供给型接口

Supplier < T> T get() 无参有返回值的抽象方法；

断定型接口

Predicate boolean test(T t):有参，但是返回值类型是固定的boolean

函数型接口

Function<T,R> R apply(T t)有参有返回值的抽象方法；