java8 stream接口终端操作 count，anyMatch，allMatch，noneMatch

妖狐艹你老母 2021-09-26 23:54 316阅读 0赞

对于中间操作和终端操作的定义，请看[《JAVA8 stream接口 中间操作和终端操作》][JAVA8 stream_]，这篇主要讲述的是stream的count，anyMatch，allMatch，noneMatch操作，我们先看下函数的定义

long count();  
      
        boolean anyMatch(Predicate<? super T> predicate);  
      
        boolean allMatch(Predicate<? super T> predicate);  
      
        boolean noneMatch(Predicate<? super T> predicate);

count方法，跟List接口的size一样，返回的都是这个集合流的元素的长度，不同的是，流是集合的一个高级工厂，中间操作是工厂里的每一道工序，我们对这个流操作完成后，可以进行元素的数量的和；

剩下的三个方法，传入的都是Predicate的函数式接口，接口定义请看[《JAVA8 Predicate接口》][JAVA8 Predicate]；

anyMatch表示，判断的条件里，任意一个元素成功，返回true

allMatch表示，判断条件里的元素，所有的都是，返回true

noneMatch跟allMatch相反，判断条件里的元素，所有的都不是，返回true

下面，看几个例子

List<String> strs = Arrays.asList("a", "a", "a", "a", "b");
            boolean aa = strs.stream().anyMatch(str -> str.equals("a"));
            boolean bb = strs.stream().allMatch(str -> str.equals("a"));
            boolean cc = strs.stream().noneMatch(str -> str.equals("a"));
            long count = strs.stream().filter(str -> str.equals("a")).count();
            System.out.println(aa);// TRUE
            System.out.println(bb);// FALSE
            System.out.println(cc);// FALSE
            System.out.println(count);// 4

通过例子可以看到，变量aa的表达式，strs里的元素，任意有“a”，表示true

变量bb的表达式，strs里的元素，全部为“a”，表示true，否则false

变量cc的表达式，strs里的元素，全部不为“a”，表示true，否则false

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先看下如下代码

public static void main(String[] args) {
            List<String> list = new ArrayList<>();
            boolean allMatch = list.stream().allMatch(e -> e.equals("a"));
            boolean anyMatch = list.stream().anyMatch(e -> e.equals("a"));
            boolean noneMatch = list.stream().noneMatch(e -> e.equals("a"));
            System.out.println(allMatch);// true
            System.out.println(anyMatch);// false
            System.out.println(noneMatch);// true
        }

最近，有小伙伴留言说，`boolean allMatch = list.stream().allMatch(e -> e.equals("a"));`

当list的为空集合时候，这个返回默认为true；按照实际的业务，理解这个的话，应该为false；然后网上搜索了一下，比较尴尬的是，很多都是抄下我之前的文章，秉承着，严谨的原则，查看了源码，下面是整个分析的过程；

详细看[《java8 stream接口终端操作allMatch 当list为空集合的一些思考》][java8 stream_allMatch _list]

## 1.lambda表达式 ##

[《java8 Lambda表达式简介》][java8 Lambda]

[《java8 lambda表达式，方法的引用以及构造器的引用》][java8 lambda]

### 2.函数式接口 ###

[《java8 函数式接口简介》][java8]

[《JAVA8 Function接口以及同类型的特化的接口》][JAVA8 Function]

[《JAVA8 Consumer接口》][JAVA8 Consumer]

[《JAVA8 Supplier接口》][JAVA8 Supplier]

[《JAVA8 UnaryOperator接口》][JAVA8 UnaryOperator]

[《JAVA8 BiConsumer 接口》][JAVA8 BiConsumer]

3.stream接口操作

[《java8 Stream接口简介》][java8 Stream]

[《 java8 Stream-创建流的几种方式》][java8 Stream-]

[《JAVA8 stream接口 中间操作和终端操作》][JAVA8 stream_]

[《JAVA8 Stream接口，map操作，filter操作，flatMap操作》][JAVA8 Stream_map_filter_flatMap]

[《JAVA8 stream接口 distinct，sorted，peek，limit，skip》][JAVA8 stream_ distinct_sorted_peek_limit_skip]

[《java8 stream接口 终端操作 forEachOrdered和forEach》][java8 stream_ _ forEachOrdered_forEach]

[《java8 stream接口 终端操作 toArray操作》][java8 stream_ _ toArray]

[《java8 stream接口 终端操作 min，max，findFirst，findAny操作》][java8 stream_ _ min_max_findFirst_findAny]

[《java8 stream接口终端操作 count，anyMatch，allMatch，noneMatch》][java8 stream_ count_anyMatch_allMatch_noneMatch]

[《java8 srteam接口终端操作reduce操作》][java8 srteam_reduce]

[《java8 stream接口 终端操作 collect操作》][java8 stream_ _ collect]

4.其他部分

[《java8 Optional静态类简介，以及用法》][java8 Optional]

[JAVA8 stream_]: https://blog.csdn.net/qq_28410283/article/details/80634725
[JAVA8 Predicate]: https://blog.csdn.net/qq_28410283/article/details/80601495
[java8 stream_allMatch _list]: https://blog.csdn.net/qq_28410283/article/details/110533469
[java8 Lambda]: https://blog.csdn.net/qq_28410283/article/details/80961022
[java8 lambda]: https://blog.csdn.net/qq_28410283/article/details/80963351
[java8]: https://blog.csdn.net/qq_28410283/article/details/80962325
[JAVA8 Function]: https://blog.csdn.net/qq_28410283/article/details/80615629
[JAVA8 Consumer]: https://blog.csdn.net/qq_28410283/article/details/80618456
[JAVA8 Supplier]: https://blog.csdn.net/qq_28410283/article/details/80625482
[JAVA8 UnaryOperator]: https://blog.csdn.net/qq_28410283/article/details/80634319
[JAVA8 BiConsumer]: https://blog.csdn.net/qq_28410283/article/details/80704487
[java8 Stream]: https://blog.csdn.net/qq_28410283/article/details/80633292
[java8 Stream-]: https://blog.csdn.net/qq_28410283/article/details/80633710
[JAVA8 Stream_map_filter_flatMap]: https://blog.csdn.net/qq_28410283/article/details/80642786
[JAVA8 stream_ distinct_sorted_peek_limit_skip]: https://blog.csdn.net/qq_28410283/article/details/80643711
[java8 stream_ _ forEachOrdered_forEach]: https://blog.csdn.net/qq_28410283/article/details/80782808
[java8 stream_ _ toArray]: https://blog.csdn.net/qq_28410283/article/details/80783286
[java8 stream_ _ min_max_findFirst_findAny]: https://blog.csdn.net/qq_28410283/article/details/80783505
[java8 stream_ count_anyMatch_allMatch_noneMatch]: https://blog.csdn.net/qq_28410283/article/details/80783946
[java8 srteam_reduce]: https://blog.csdn.net/qq_28410283/article/details/80873910
[java8 stream_ _ collect]: https://blog.csdn.net/qq_28410283/article/details/81052881
[java8 Optional]: https://blog.csdn.net/qq_28410283/article/details/80952768