Streams是在Java中引入的,旨在帮助开发人员从一系列对象中执行聚合操作.使用Java 9,添加更多方法可以使流更好.
default Stream<T> takeWhile(Predicate<? super T> predicate)
takeWhile方法获取所有值,直到谓词返回false.在有序流的情况下,它返回一个流,该流包含从该流中获取的与给定谓词匹配的最长元素前缀.
import java.util.stream.Stream; public class Tester { public static void main(String[] args) { Stream.of("a","b","c","","e","f").takeWhile(s->!s.isEmpty()) .forEach(System.out::print); } }
takeWhile方法占用所有a,b和c值,然后一旦字符串为空,它就会停止执行.
abc
default Stream<T> dropWhile(Predicate<? super T> predicate)
dropWhile方法在开始时抛弃所有值,直到谓词返回true.在有序流的情况下,它在丢弃与给定谓词匹配的元素的最长前缀之后返回由该流的剩余元素组成的流.
import java.util.stream.Stream; public class Tester { public static void main(String[] args) { Stream.of("a","b","c","","e","f").dropWhile(s-> !s.isEmpty()) .forEach(System.out::print); System.out.println(); Stream.of("a","b","c","","e","","f").dropWhile(s-> !s.isEmpty()) .forEach(System.out::print); } }
dropWhile方法删除a,b和c值,然后一旦字符串为空,它将获取所有值.
ef ef
static <T> Stream<T> iterate(T seed, Predicate<? super T> hasNext, UnaryOperator<T> next)
iterate方法现在有hasNext谓词作为参数,它停止循环一次hasNext谓词返回false.
import java.util.stream.IntStream; public class Tester { public static void main(String[] args) { IntStream.iterate(3, x -> x < 10, x -> x+ 3).forEach(System.out::println); } }
3 6 9
static <T> Stream<T> ofNullable(T t)
ofNullable方法用于防止NullPointerExceptions并避免对流进行空检查.此方法返回包含单个元素的顺序Stream,如果非null,否则返回空Stream.
import java.util.stream.Stream; public class Tester { public static void main(String[] args) { long count = Stream.ofNullable(100).count(); System.out.println(count); count = Stream.ofNullable(null).count(); System.out.println(count); } }
1 0