Java8 接口初始化的几种场景

通过接口实现类的方式实现

代码实现

public interface MyService {

    void sayMessage(String message);

    default void doWork1() { System.out.println("doWork"); }

    static void printHello() {System.out.println("Hello"); }
}

//接口实现
public class MyServiceImpl implements MyService{

    @Override
    public void sayMessage(String message) {
        System.out.println(message);
    }

}

//测试方法
MyService myService=new MyServiceImpl();

myService.sayMessage("hello,welcome");
 //hello,welcome

通过匿名内部类的来实现

代码实现

 MyService myService=new MyService(){

            @Override
            public void sayMessage(String message) {
                  System.out.println(message);
            }

        };


//测试方法
myService.sayMessage("hello,welcome");
 //hello,welcome

通过JDK8 双冒号用法方式

代码实现

void showMessage(String mssage){
        System.out.println(mssage);
    }

MyService myService3=this::showMessage;
myService3.sayMessage("hello,jack");

通过箭头函数Lambda表达式的方式

代码实现

//定义函数式接口
@FunctionalInterface
public interface YourService<T,R> {

    List<R> map(List<T> src, Function<T, R> mapper, Class<R> targetType);

}

/*@FunctionalInterface 注解申明一个函数式接口，这样就可以采用箭头函数的方式来实现接口，如果接口中默认只定义了一个方法，则@FunctionalInterface注解可以省略
*/

// 接口实现
//通过箭头函数Lambda表达式来实现
YourService<Student, Person> ysImpl = (item1, item2, item3) -> {
    List<Person> persons2 = new ArrayList<Person>();
    for (Student stu : item1) {
        persons2.add(item2.apply(stu));
    }
    return persons2;
};

//测试
List<Student> students = new ArrayList<Student>() {
            {
                add(new Student(0, 10, "a"));
                add(new Student(1, 20, "b"));
                add(new Student(2, 30, "c"));
                add(new Student(3, 40, "d"));
            }
        };

  List<Person> personsBew = ysImpl.map(students, (r) -> {
            Person person = new Person();
            BeanUtils.copyProperties(r, person);
            return person;
        }, Person.class);

System.out.println(personsBew.toString());

[TestRunner.Person(id=0, age=10, firstName=a), TestRunner.Person(id=1, age=20, firstName=b), TestRunner.Person(id=2, age=30, firstName=c), TestRunner.Person(id=3, age=40, firstName=d)]

将接口作为方法参数

代码实现

    //将接口作为方法形参
    private <T, R> void testMethod(List<T> rList, YourService<T, R> service, Class<R> target) {
        
        List<R> rlist = service.map(rList, (t) -> {
            R r = null;
            try {
                
                r = (R) target.newInstance();
                BeanUtils.copyProperties(t, r);
            } catch (InstantiationException | IllegalAccessException e) {

                e.printStackTrace();
                System.out.println(e.toString());
            }
            return r;
        }, target);
        System.out.println(rlist.toString());
    }

//调用方法并实现接口方法
testMethod(students, (item1, item2, item3) -> {
    List<Person> persons2 = new ArrayList<Person>();
    for (Student stu : item1) {
        persons2.add(item2.apply(stu));
    }
    return persons2;
}, Person.class);