Java中Lambda表达式的使用详解

/**
 * lambdab表达式的发展
 */
public class TestLambda1 {
    //3.静态内部类
    static class Like2 implements ILike{
        @Override
        public void lambda() {
            System.out.println("i like lambda2");
        }
    }

    public static void main(String[] args) {
        ILike like=new Like();
        like.lambda();

        like=new Like2();
        like.lambda();

        //4.局部内部类
       class Like3 implements ILike{
            @Override
            public void lambda() {
                System.out.println("i like lambda3");
            }
        }
        like=new Like3();
        like.lambda();

        //5.匿名内部类
        like=new ILike() {
            @Override
            public void lambda() {
                System.out.println("i like lambda4");
            }
        };
        like.lambda();

        //6.用lambda简化
        like=()->{
            System.out.println("i like lambda5");
        };
        like.lambda();
    }
}

//1.定义一个函数式接口
interface ILike{
    void lambda();
}

//2.实现类
class Like implements ILike{

    @Override
    public void lambda() {
        System.out.println("i like lambda");
    }
}

// 1. 不需要参数,返回值为 5  
() -> 5  
  
// 2. 接收一个参数(数字类型),返回其2倍的值  
x -> 2 * x  
  
// 3. 接受2个参数(数字),并返回他们的差值  
(x, y) -> x – y  
  
// 4. 接收2个int型整数,返回他们的和  
(int x, int y) -> x + y  
  
// 5. 接受一个 string 对象,并在控制台打印,不返回任何值(看起来像是返回void)  
(String s) -> System.out.print(s)

public class java8_Lambda_Test {
    public static final void main(String[] args) {

        Operator addOper = (a, b) -> a + b;
        Operator reduceOper = (a, b) -> a - b;
        Operator multiplyOper = (a, b) -> a * b;
        Operator DivideOper = (a, b) -> a / b;

        java8_Lambda_Test test = new java8_Lambda_Test();
        System.out.println(test.getResult(3, 3, addOper));//6
        System.out.println(test.getResult(3, 3, reduceOper));//0
        System.out.println(test.getResult(3, 3, multiplyOper));//9
        System.out.println(test.getResult(3, 3, DivideOper));//1
    }

    public int getResult(int a, int b, Operator operator) {
        return operator.convert(a, b);
    }

    public interface Operator {
        int convert(int a, int b);
        default int get(int a) {
            return a;
        }
    }
}

public class Student implements Comparable<Student>{
    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

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

    @Override
    public int compareTo(Student student2) {
       int result =this.age - student2.age;
       return result;
    }
}

        List<Student> list=new ArrayList<>();
        Student s1=new Student();
        s1.setName("张三");
        s1.setAge(28);
        list.add(s1);
        Student s=new Student();
        s.setName("李四");
        s.setAge(22);
        list.add(s);
        sortUsingJava8(list);

        list.forEach((student) -> System.out.println(student.getName() + ":"+student.getAge()));

 // 使用 java 8 排序
    static void sortUsingJava8(List<Student> list){
        Collections.sort(list, (student1, student2) -> student1.compareTo(student2));
    }

    // 使用 java 7 排序
    private void sortUsingJava7(List<String> list){
        Collections.sort(list, new Comparator<String>() {
           @Override
           public int compare(String s1, String s2) {
                return s1.compareTo(s2);
            }
        });
    }

//先准备一个集合
        List<Student> list=new ArrayList<>();
        Student s1=new Student();
        s1.setName("张三");
        s1.setAge(28);
        list.add(s1);
        Student s=new Student();
        s.setName("李四");
        s.setAge(22);
        list.add(s);
//使用 lambda 表达式以及函数操作(functional operation)
  list.forEach((student) -> System.out.println(student.getName() + ":"+student.getAge()));

 //带条件 打印年龄大于等于20的学生的姓名
        list.forEach((student)->{
            if (student.getAge()>=20)
                System.out.println(student.getName());
                });

Runnable r = new Runnable() {
    @Override
    public void run() {
        //to do something
    }
};
Thread t = new Thread(r);
t.start();

Runnable r = () -> {
    //to do something
};
Thread t = new Thread(r);
t.start();

Thread t = new Thread(() -> {
    //to do something
    // such as for
    for(int i = 0; i < 100; i++){
        System.out.println(i);
           }
});
t.start;