lambda表达式
语法
最常用的:
Runnable runnable = () -> System.out.println("Hello!");
Thread t = new Thread(runnable);
t.start();
t.join();
你还可以这么写:
Thread t = new Thread(() -> System.out.println("Hello!"));
t.start();
t.join();
带有参数的呢?
Comparator<String> stringComparator = (s1, s2) -> s1.compareTo(s2); 扩展成一个完整的表达式: Comparator<String> stringComparator = (String s1, String s2) -> { System.out.println("Comparing..."); return s1.compareTo(s2); }; |
函数式接口
Lambda表达式使得你可以更紧凑地表达出单方法类。单一方法类也被称作函数式接口,它可以通过
@FunctionalInterface来进行注解:
@FunctionalInterface public interface MyFunctionalInterface<T> { boolean test(T t); } // Usage MyFunctionalInterface<String> l = s -> s.startsWith("A"); |
方法引用
方法引用就是更紧凑,易懂的Lambda表达式,它适用于那些已经有名字的方法。来看一个简单的例子:
public class Sample { public static void main(String[] args) { Runnable runnable = Sample::run; } private static void run() { System.out.println("Hello!"); } } |
还有一个:
public static void main(String[] args) { Sample sample = new Sample(); Comparator<String> stringLengthComparator = sample::compareLength; } private int compareLength(String s1, String s2) { return s1.length() - s2.length(); } |
Stream API基础
stream是一个元素序列,它支持串行及并行的操作。
遍历列表
List<String> list = Arrays.asList("one", "two", "three", "four", "five", "six");
list.stream()
.forEach(s -> System.out.println(s));