1、Lambda表达式简单说就是一个方法

2、它可以作为参数在方法见传递

3、但只能在使用了FunctionalInterface的地方

4、FunctionalInterface是单个方法的接口，且使用了@FunctionalInterface的注解

5、Lambda的好处是语法简洁，同时在多核CPU下运行效率高

6、Lambda表达式的语法
基本语法:
(parameters) -> expression或
(parameters) ->{ statements; }

实例：
一：runnable接口符合Lambda的要求（3和4点就是使用Lambda表达式的基本要求）

Runnable.class

public class LearnLambda1 {
    public static void main(String [] args){
        for(int i = 0; i<1000; i++)
            new Thread(()->
            System.out.println("I am thread "+Thread.currentThread().getId())).start();
    }
}

二、List.forEach(Consumer c)中的Consumer接口也是只有一个方法，并且使用了@FunctionalInterface的注解

public class LearnLambda2 {
    public static void main(String [] args){
        List<Person> persons = new ArrayList<Person>();
        persons.add(new Person("张三","化学",60));
        persons.add(new Person("李四","生物",78));
        persons.add(new Person("王五","物理",69));
        persons.add(new Person("钱六","计算机",83));
        persons.add(new Person("赵七","英语",90));
        
        persons.forEach((Person p)->System.out.println(p.name));
        System.out.println();
        persons.forEach((Person p)->System.out.println(p.name + ":" + p.department));
        System.out.println();
        persons.forEach((Person p)->System.out.println(p.name + ":" + p.score));
    }
}
public class Person {
    public String name;
    public String department;
    public int score;
    public Person(String name, String department, int score) {
        this.name = name;
        this.department = department;
        this.score = score;
    }
}

三、Predicate接口也是也是只有一个方法，并且使用了@FunctionalInterface的注解(接口详细信息请看API)

public class LearnLambda3 {
    public static void main(String [] args){
        List<Person> persons = new ArrayList<Person>();
        persons.add(new Person("张三","化学",60));
        persons.add(new Person("李四","生物",78));
        persons.add(new Person("王五","物理",69));
        persons.add(new Person("钱六","计算机",83));
        persons.add(new Person("赵七","化学",90));
//      filterPrint(persons,(Person p)->p.department.equals("化学"));
        filterPrint(persons,(Person p)->p.score>70);
    }
    public static void filterPrint(List<Person> persons,Predicate<Person> predicate){
        for(Person p : persons){
            if(predicate.test(p))
                System.out.println(p.name);
        }
    }
}

四、当然我们可以自定义接口来使用lambda

@FunctionalInterface
interface Studey{
    void studing();
}
public class LearnLambda4 {
    public static void doSomething(Studey study){//可以有多个参数，方法内容也可以自定义
        study.studing();
    }
    public static void main(String [] args){
        doSomething(()->System.out.println("我正在学习lambda"));
    }
}