检查筛选器找到任何项目并获取第一个项目

Question

Stream<String> res= Stream.of("a1", "a2", "b1", "c2", "c1")
.filter(s -> s.startsWith("c"));

if(res.anyMatch(i->true))
     System.out.println(res.findFirst().get());

Answer 1

使用findfirst和ifpresent:

Stream.of("a1", "a2", "b1", "c2", "c1")
      .filter(s -> s.startsWith("c"))
      .findFirst()
      .ifPresent(System.out::println);

或者如果要执行另一个操作，如果findfirst()返回一个空的可选的 ，则使用

Optional<String> result =
    Stream.of("a1", "a2", "b1", "c2", "c1")
          .filter(s -> s.startsWith("c"))
          .findFirst();
if(result.isPresent()){ System.out.println(result.get());}
else{ System.out.println("nothing found");};

或者从JDK9开始-

 Stream.of("a1", "a2", "b1", "c2", "c1")
       .filter(s -> s.startsWith("c"))
       .findFirst()
       .ifPresentOrElse(System.out::println, () -> System.out.println("nothing found"));