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;