Java8的Lambda表达式你真的会吗

class Task implements Runnable{

 @Override
 public void run() {
  System.out.println("Java8 之前 实现Runnable接口中的run方法");
 }
}
Runnable t = new Task();

Runnable taskBeforeJava8 = new Runnable() {
 @Override
 public void run() {
  System.out.println("Java8 之前的写法, 传入匿名类");
 }
};

// java8 之后
Runnable taskAfterJava8 = () -> System.out.println("Java8 之后的写法,lambda表达式");

(parameters) -> action
 (parameters) -> expression
 (parameters) -> {statements;}

@FunctionalInterface // 此注解作用的接口 只能拥有一个抽象方法
public interface Runnable {
 public abstract void run();
}

@FunctionalInterface // 此注解作用的接口 只能拥有一个抽象方法
public interface Runnable {
 public abstract void run();
}

/**
  * 供给型接口, 无参数,返回T
  */
 public static void supplierTest() {
  Supplier<Object> supplier = () -> new Object();
  System.out.println(supplier.get());
 }

 /**
  * 断言型 传入参数T ,返回boolean
  */
 public static void predicateTest() {
  Predicate<String> predicate = name -> name.startsWith("summer");
  System.out.println(predicate.test("summerday"));
 }

 /**
  * 函数型接口 传入T 返回R
  */
 public static void functionTest() {
  List<Integer> list = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
  Function<List<Integer>, Integer> function = num -> {
   int res = 0;
   for (int n : list) {
    res += n;
   }
   return res;
  };
  Integer num = function.apply(list);
  System.out.println(num);
 }

/**
 * 方法引用
 * 1. 指向静态方法的方法引用
 * 2. 指向现有对象的实例方法的方法引用
 *
 * @author Summerday
 */
public class MethodReferenceTest {
	
 public static List<String> getList(List<String> params, Predicate<String> filter) {
  List<String> res = new LinkedList<>();
  for (String param : params) {
   if (filter.test(param)) {
    res.add(param);
   }
  }
  return res;
 }
 // 静态方法
 public static boolean isStartWith(String name) {
  return name.startsWith("sum");
 }

 public static void main(String[] args) {
  List<String> params = Arrays.asList("summerday","tqbx","天乔巴夏","summer","");
  //静态方法的方法引用 getList(params, name -> MethodReferenceTest.isStartWith(name));
  List<String> list = getList(params, MethodReferenceTest::isStartWith);
  System.out.println(list);
  
  // 指向现有对象的实例方法的方法引用 getList(params, name -> name.isEmpty());
  List<String> sum = getList(params, String::isEmpty);
  System.out.println(sum);
  
 }
}

/**
 * 数组引用
 * @author Summerday
 */
public class ArrayReferenceTest {

 public static void main(String[] args) {
  // 普通lambda
  Function<Integer,String[]> fun1 = x -> new String[x];
  String[] res1 = fun1.apply(10);
  System.out.println(res1.length);

  // 数组引用写法
  Function<Integer,String[]> fun2 = String[]::new;
  String[] res2 = fun2.apply(10);
  System.out.println(res2.length);

 }
}

/**
 * 构造器引用
 * @author Summerday
 */
public class ConstructorReferenceTest {

 public static void main(String[] args) {

  // 普通lambda
  Supplier<User> sup = () -> new User();

  // 构造器引用
  Supplier<User> supplier = User::new;
  User user = supplier.get();
  System.out.println(user);
 }

}

class User{

}