java 下划线

In this post, we will discuss about What is the use of Underscore (“_”) in Java Modifiers? Changes to underscore in Java SE 9 release with some simple and useful examples. I have already released many Java SE 9 tutorials. Please go through them to learn all Java SE 9 new features.

在本文中，我们将讨论Java修饰符中下划线（“ _”）的用法是什么？ Java SE 9版本中对下划线的更改带有一些简单而有用的示例。 我已经发布了许多Java SE 9教程。 请通过他们学习所有Java SE 9的新功能。

Recently Oracle Corp has changed the release date of Java SE 9 from March 2017 to July 2017.

最近，Oracle Corp将Java SE 9的发布日期从2017年3月更改为2017年7月。

Let us start this post now.

让我们现在开始这篇文章。

Java下划线（“ _”）简介 (Introduction to Underscore (“_”) in Java)

In Java, we can start an identifier with a letter, dollar sign ($) or underscore (“_”). However, Identifiers cannot start with a number.

在Java中，我们可以以字母，美元符号（$）或下划线（“ _”）开头的标识符。 但是，标识符不能以数字开头。

In Java, we can use underscore in identifiers mainly the following cases:

在Java中，主要在以下情况下，我们可以在标识符中使用下划线：

• To connect two different words of an identifier.连接标识符的两个不同单词。
• To define constants.定义常量。
• To define some lengthy and useful identifier (mostly in unit tests).定义一些冗长而有用的标识符（主要在单元测试中）。
• To define private variables, methods etc.定义私有变量，方法等

在Java SE 8之前：下划线（“ _”） (Before Java SE 8: Underscore (“_”))

Before Java SE 8 release, we can use Underscore in identifiers. And also we can use Underscore alone as an identifier without any issues. Even though it is not recommended, but it works fine without any issues.

在Java SE 8发行之前，我们可以在标识符中使用Underscore。 而且我们也可以单独使用Underscore作为标识符，而不会出现任何问题。 即使不建议这样做，但它可以正常工作而不会出现任何问题。

Java SE 8：“ _”更改 (Java SE 8: “_” Changes)

In Java SE 8 release, using Underscore alone as an identifier is not recommended and it gives a WARNING message. To test it, write a simple Java program in any IDEs like Eclipse and run it.

在Java SE 8发行版中，建议不要单独使用Underscore作为标识符，它会给出警告消息。 要对其进行测试，请在诸如Eclipse之类的所有IDE中编写一个简单的Java程序并运行它。

Example:-

例：-

public class Java8UnderscoreTest
{public static void main(String[] args) {int _ = 10;System.out.println("Value of underscore (_) = " + _);}
}

Output:-

输出：-

Value of underscore (_) = 10

It works fine without any issues. However, we can see the following warning messages in IDEs.

它工作正常，没有任何问题。 但是，我们可以在IDE中看到以下警告消息。

Multiple markers at this line
- '_' should not be used as an identifier, since it is a reserved keyword from source level 1.8 on
- Occurrence of '_'

That means Underscore is not allowed as an identifier from Java SE 8 on-wards.

这意味着从Java SE 8开始不允许使用下划线作为标识符。

NOTE:-

注意：-

It is a compile-time error if a Lambda Parameter has the name underscore (“_”).

如果Lambda参数的名称下划线（“ _”），则是编译时错误。

Java SE 9：“ _”更改 (Java SE 9: “_” Changes)

Oracle Corp is going to remove that underscore (“_”) usage as identifier completely in Java SE 9 release.

Oracle Corp将在Java SE 9发行版中完全删除下划线（_）用作标识符。

NOTE:- Disallowing “_” as a legal identifier

注意：-禁止将“ _”作为合法标识符

jshell> int _ = 10
|  Error:
|  as of release 9, '_' is a keyword, and may not be used as an identifier
|  int _ = 10
|      ^
|  Error:
|  reached end of file while parsing
|  int _ = 10

That’s it all about “Java SE 9: Underscore Changes”. We will discuss some more Java SE 9 New Features in my coming posts.

关于“ Java SE 9：下划线更改”的全部内容。 我们将在以后的文章中讨论更多Java SE 9新功能。

Please drop me a comment if you like my post or have any issues/suggestions/type errors.

如果您喜欢我的帖子或有任何问题/建议/类型错误，请给我评论。

Thank you for reading my tutorials.

感谢您阅读我的教程。

Happy Java SE 9 Learning!

Java SE 9学习愉快！

翻译自: https://www.journaldev.com/13563/javase9-underscore-changes

java 下划线