blocks|key|5611979|text|这是一个匿名内部类。它正在使用大括号中的代码创建Runnable接口的实现。除了实现接口之外，您还可以扩展其他类。好的方面是，您可以在不显式创建单独的类的情况下做到这一点，并且还可以在匿名内部类的主体中引用final局部变量(包括参数)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5611980|有关更多详细信息，请参阅Java+tutorial，或者只需搜索“匿名内部类”即可获得大量相关页面。|5611981|entityMap|0|LINK|mutability|MUTABLE|url|http://download.oracle.com/javase/tutorial/java/javaOO/innerclasses.html^0|O|8|2V|5|0|C|D|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@]|D|@$9|V|A|W|1|X]]|E|$]]|$1|H|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

That's an anonymous inner class. It's creating an implementation of the <code>Runnable</code> interface using code within the braces. As well as implementing interfaces, you can extend other classes. The nice aspects are that you can do this without explicitly creating a separate class, and you can also refer to <code>final</code> local variables (including parameters) within the body of the anonymous inner class.

See the <a href="http://download.oracle.com/javase/tutorial/java/javaOO/innerclasses.html">Java tutorial</a> for more details, or just search for "anonymous inner class" for loads of related pages.

blocks|key|1510034|text|正如其他人所提到的，这里创建的是一个匿名内部类。具体地说，编写代码的人说：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1510035|运行而不是Runnable类的实例，我想创建一个覆盖“|1510036|+()”方法的子类，并创建它的一个实例。不值得我花时间去创建一个命名的子类，因为我只打算创建这个实例。相反，只需覆盖该方法并返回我需要的子类实例。|blockquote|1510037|1510038|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|-4|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

As mentioned by others, what is being created here is an anonymous inner class. Specifically, the person who wrote the code is saying:

<blockquote>
 Instead of an instance of the Runnable class, I want to create a subclass that overrides the "run()" method and create an instance of that. Its not worth my time to create a named subclass, since I'm only going to create this one instance. Instead, just override the method and return the subclass instance I need.
</blockquote>

blocks|key|1827220|text|这是一个anonymous+class声明--基本上就是一个实现Runnable接口的类，作为一个匿名嵌套类进行声明和实例化。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1827221|注意，你也可以用同样的方式声明匿名子类：|1827222|Object+o+=+new+Object(){
++++public+String+toString(){+return+"boo!"+};
}|code-block|syntax|javascript|1827223|还要注意，您可以在匿名类代码中使用封闭方法的变量，但前提是变量为final+(因为匿名类实际上获得了变量的副本)。|1827224|entityMap|0|LINK|mutability|MUTABLE|url|http://docstore.mik.ua/orelly/java-ent/jnut/ch03_12.htm^0|W|8|4|F|0|0|0|0|W|5|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|F|3|G|5|6|7|12|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|13|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|14|8|@$9|15|A|16|B|C]]|D|@]|E|$]]|$1|O|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

That's an <a href="http://docstore.mik.ua/orelly/java-ent/jnut/ch03_12.htm" rel="nofollow">anonymous class</a> declaration - basically, a class that implements the <code>Runnable</code> interface, declared and instantiated inline as an anonymous nested class.

Note that you can also declare anonymous subclasses the same way:

<pre><code>Object o = new Object(){
 public String toString(){ return "boo!" };
}
</code></pre>

Also note that you can use variables of the enclosing method inside the anonymous class code, but only if the variables are <code>final</code> (because the anonymous class actually gets a copy of the variable).

blocks|key|1827090|text|我会从这2300万个http://www.google.co.uk/search?q=anonymous%2Bclasses%2Btutorial结果开始。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1827091|基本上，它允许您定义一个实现或一个子类，而不必创建一个完整的类定义。|1827092|编辑:为了你自己的兴趣，看看你是否能弄清楚这是做什么的。|1827093|Map<String,+String>+map+=+new+LinkedHashMap<String,+String>()+{{+//+two+brackets
+++put("a",+"aye");
+++put("b",+"bee");
+++put("c",+"see");
+++put("d",+"dee");
+++put("e",+"ee");
+++put("f",+"eff");
}};|code-block|syntax|javascript|1827094|entityMap|0|LINK|mutability|MUTABLE|url|http://www.google.co.uk/search?q=anonymous%2Bclasses%2Btutorial^0|A|1N|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|Z|8|@]|9|@]|C|$]]|$1|H|3|I|5|J|7|10|8|@]|9|@]|C|$K|L]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

I would start with these <a href="http://www.google.co.uk/search?q=anonymous+classes+tutorial" rel="nofollow">http://www.google.co.uk/search?q=anonymous+classes+tutorial</a> 23 million results.

Basically, it allows you to define an implementation or a subclass without having to create a fully formed class defintiions.

EDIT: For your own interest, see if you can figure out what this does.

<pre><code>Map&lt;String, String&gt; map = new LinkedHashMap&lt;String, String&gt;() {{ // two brackets
 put("a", "aye");
 put("b", "bee");
 put("c", "see");
 put("d", "dee");
 put("e", "ee");
 put("f", "eff");
}};
</code></pre>

blocks|key|4143619|text|这就是所谓的“匿名类”。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4143620|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It's so called 'anonymous class'.

blocks|key|1515427|text|您可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1515428|++class+MyRunnable+implements+Runnable{
+++++public+void+run()+{
++++++++System.out.println("Hello");
+++++}
++}|code-block|syntax|javascript|1515429|然后：|1515430|+Runnable+r+=+new+MyRunnable();|1515431|并达到同样的效果。但是，在代码的任何其他部分中都不需要您创建的MyRunnable类。所以没有必要创建一个命名类。另一方面，您编写的代码正在创建一个匿名内部类，以便类的实现恰好位于需要它的位置。它不会在代码中的任何其他地方访问rom，但这就是你的想法，你不需要它在其他任何地方。|1515432|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

You can do this:

<pre><code> class MyRunnable implements Runnable{
 public void run() {
 System.out.println("Hello");
 }
 }
</code></pre>

Then:

<pre><code> Runnable r = new MyRunnable();
</code></pre>

And achieve the same thing. However, the MyRunnable class that you created is never needed in any other part of your code. So creating a named class is not necessary. The code that you wrote on the other hand is creating an anonymous inner class such that the implementation of the class is precisely where it is needed. It will not be accessible rom anywhere else in the code but that is the idea, you do not need it anywhere else.

Though i have often come across,i dont understand this way of writing code:

<pre><code>Runnable r=new Runnable() {//&lt;----- (braces start here?)
 public void run() {
 System.out.println("Hello");
 }
}; // ?
</code></pre>

What is this?
Please explain very clearly.

This Way of Writing?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

虽然我经常遇到，但我不理解这种编写代码的方式：Runnable r=new Runnable() {//<----- (braces start here?) public void run() { System.out.println("Hello"); }}; // ?这是什么？请解释清楚。

问这种写作方式？
EN

回答 6

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问这种写作方式？EN

回答 6

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问这种写作方式？
EN