klion26 commented on a change in pull request #9348: [FLINK-13505][docs-zh]
Translate "Java Lambda Expressions" page into Chinese
URL: https://github.com/apache/flink/pull/9348#discussion_r311408129
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File path: docs/dev/java_lambdas.zh.md
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@@ -22,41 +22,37 @@ specific language governing permissions and limitations
under the License.
-->
-Java 8 introduced several new language features designed for faster and
clearer coding. With the most important feature,
-the so-called "Lambda Expressions", it opened the door to functional
programming. Lambda expressions allow for implementing and
-passing functions in a straightforward way without having to declare
additional (anonymous) classes.
+Java 8 引入了几种新的语言特性，旨在实现更快、更清晰的编码。 作为最重要的特性，即所谓的“Lambda
表达式”，它开启了函数式编程的大门。Lambda 表达式允许以简捷的方式实现和传递函数，而无需声明额外的（匿名）类。
-<span class="label label-danger">Attention</span> Flink supports the usage of
lambda expressions for all operators of the Java API, however, whenever a
lambda expression uses Java generics you need to declare type information
*explicitly*.
+<span class="label label-danger">注意</span> Flink 支持对 Java API 的所有算子使用 Lambda
表达式，但是，当 Lambda 表达式使用 Java 泛型时，你需要*显式*声明类型信息。
-This document shows how to use lambda expressions and describes current
limitations. For a general introduction to the
-Flink API, please refer to the [Programming Guide]({{ site.baseurl
}}/dev/api_concepts.html)
+本文档介绍了如何使用 Lambda 表达式并描述了其在当前应用中的限制。有关 Flink API 的一般性介绍， 请参阅[编程指南]({{
site.baseurl }}/zh/dev/api_concepts.html)。
-### Examples and Limitations
+### 示例和限制
-The following example illustrates how to implement a simple, inline `map()`
function that squares its input using a lambda expression.
-The types of input `i` and output parameters of the `map()` function need not
to be declared as they are inferred by the Java compiler.
+下例演示了如何实现一个简单的行内 `map()` 函数，它使用 Lambda 表达式计算输入的平方。不需要声明 `map()` 函数的输入 `i`
和输出参数的数据类型，因为 Java 编译器会对它们做出推断。
{% highlight java %}
env.fromElements(1, 2, 3)
-// returns the squared i
+// 返回 i 的平方
.map(i -> i*i)
.print();
{% endhighlight %}
-Flink can automatically extract the result type information from the
implementation of the method signature `OUT map(IN value)` because `OUT` is not
generic but `Integer`.
+由于 `OUT` 是 `Integer` 而不是泛型，Flink 可以由方法签名 `OUT map(IN value)` 的实现中自动提取出结果的类型信息。
-Unfortunately, functions such as `flatMap()` with a signature `void flatMap(IN
value, Collector<OUT> out)` are compiled into `void flatMap(IN value, Collector
out)` by the Java compiler. This makes it impossible for Flink to infer the
type information for the output type automatically.
+不幸的是，`flatMap()` 这样的函数，它的签名 `void flatMap(IN value, Collector<OUT> out)` 被
Java 编译器编译为 `void flatMap(IN value, Collector out)`。这样 Flink 就无法自动推断输出的类型信息了。
-Flink will most likely throw an exception similar to the following:
+Flink 很可能抛出类似如下的异常：
{% highlight plain%}
org.apache.flink.api.common.functions.InvalidTypesException: The generic type
parameters of 'Collector' are missing.
- In many cases lambda methods don't provide enough information for
automatic type extraction when Java generics are involved.
+ In many cases Lambda methods don't provide enough information for
automatic type extraction when Java generics are involved.
An easy workaround is to use an (anonymous) class instead that implements
the 'org.apache.flink.api.common.functions.FlatMapFunction' interface.
Otherwise the type has to be specified explicitly using type information.
{% endhighlight %}
-In this case, the type information needs to be *specified explicitly*,
otherwise the output will be treated as type `Object` which leads to
unefficient serialization.
+在这种情况下，需要*显式*指定类型信息，否则输出将被视为 `Object` 类型，这会导致低效的序列化。
Review comment:
maybe "要*显式*指" -> "要 *显式* 指"
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