YngwieWang 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_r312387424
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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.
Review comment:
非常感谢，你真细心。因为我翻译的时候统一把“lambda”翻译成“Lambda”，可能是不小心整体替换了，已经修正了。另外你觉得翻译的 lambda
全部首字母大写是否合适？因为我觉得翻译以后有的大写有的小写不统一的话有可能造成困惑。再次感谢！
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