blocks|key|4727120|text|类java.io.File的构造函数不在磁盘上创建文件。它只是对文件路径的抽象。该文件是在写入文件时创建的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4727121|当您创建FileWriter时，它调用FileOutputStream的构造函数，该构造函数调用一系列安全检查，然后调用：|4727122|if+(append)+{
++++openAppend(name);
}+else+{
++++open(name);
}|code-block|syntax|javascript|4727123|调用open()会在磁盘上创建文件。|4727124|编辑：|4727125|下面是open()的定义：|4727126|/**
+*+Opens+a+file,+with+the+specified+name,+for+writing.
+*+@param+name+name+of+file+to+be+opened
+*/
private+native+void+open(String+name)+throws+FileNotFoundException;|4727127|entityMap^0|1|C|0|4|A|J|G|0|0|2|6|0|0|3|6|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|14|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|15|8|@$9|16|A|17|B|C]]|D|@]|E|$]]|$1|O|3|P|5|6|7|18|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|S|3|T|5|J|7|1C|8|@]|D|@]|E|$K|L]]|$1|U|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|V|$]]

Constructor of Class <code>java.io.File</code> does not create file on disk. It is just a abstraction over the file path. The file is created when you write to the file. 

When you are creating <code>FileWriter</code> it calls constructor of <code>FileOutputStream</code> that calls a sequence of security checks and then invokes:

<pre><code>if (append) {
 openAppend(name);
} else {
 open(name);
}
</code></pre>

Invocation of <code>open()</code> creates file on disk.

EDIT:

Here is how <code>open()</code> is defined:

<pre><code>/**
 * Opens a file, with the specified name, for writing.
 * @param name name of file to be opened
 */
private native void open(String name) throws FileNotFoundException;
</code></pre>

blocks|key|4727139|text|File对象只是表示文件在系统中的位置(URL)。您可以在File对象上调用createNewFile()以便写入我们的文件，假设该位置中不存在具有该名称的文件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4727140|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|$]]

The File object is simply a representation of a file's location (URL) in the system. You can call createNewFile() on a File object in order to write our a file assuming one with that name does not already exist in that location.

blocks|key|1922468|text|File并不总是需要表示实际的文件，它可以是您计划创建的文件，可以是猜测存在的文件，也可以是您已经删除的文件。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1922469|从java.io.File的JavaDoc|1922470|1922471|是文件和目录路径名的抽象表示形式。|blockquote|1922472|1922473|1922474|和|1922475|此类的|1922476|实例可能表示也可能不表示实际的文件系统对象，如文件或目录。|1922477|1922478|1922479|为了实际创建文件，需要调用createNEwFile()，根据JavaDoc：|1922480|当且仅当具有此抽象路径名的文件尚不存在时，|1922481|才以原子方式创建一个以此抽象路径名命名的新空文件。|1922482|1922483|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/6/docs/api/java/io/File.html^0|0|4|0|1|C|0|0|0|0|0|0|0|0|0|0|0|D|F|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1A|8|@$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1D|8|@]|D|@$9|1E|A|1F|1|1G]]|E|$]]|$1|H|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]|$1|I|3|J|5|K|7|1I|8|@]|D|@]|E|$]]|$1|L|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]|$1|N|3|O|5|6|7|1L|8|@]|D|@]|E|$]]|$1|P|3|Q|5|6|7|1M|8|@]|D|@]|E|$]]|$1|R|3|S|5|K|7|1N|8|@]|D|@]|E|$]]|$1|T|3|-4|5|6|7|1O|8|@]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1P|8|@]|D|@]|E|$]]|$1|V|3|W|5|6|7|1Q|8|@$9|1R|A|1S|B|C]]|D|@]|E|$]]|$1|X|3|Y|5|6|7|1T|8|@]|D|@]|E|$]]|$1|Z|3|10|5|K|7|1U|8|@]|D|@]|E|$]]|$1|11|3|-4|5|6|7|1V|8|@]|D|@]|E|$]]|$1|12|3|-4|5|6|7|1W|8|@]|D|@]|E|$]]]|13|$14|$5|15|16|17|E|$18|19]]]]

<code>File</code> doesn't always need to represent an actual file, it can be something you plan on creating, are guessing at the existence of, or something you've deleted as well.

From the JavaDoc for <a href="http://docs.oracle.com/javase/6/docs/api/java/io/File.html" rel="nofollow">java.io.File</a>:

<blockquote>
 An abstract representation of file and directory pathnames.
</blockquote>

and

<blockquote>
 Instances of this class may or may not denote an actual file-system object such as a file or a directory. 
</blockquote>

In order to have the file actually be created, one needs to call <code>createNEwFile()</code>, whic according to the JavaDoc:

<blockquote>
 Atomically creates a new, empty file named by this abstract pathname if and only if a file with this name does not yet exist.
</blockquote>

blocks|key|1922494|text|当FileWriter在内部创建新的File对象时，这并不是导致文件存在的原因。这发生在代码的其他部分。File对象只是指定文件(或目录)的标准方法，无论它是否存在。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1922495|entityMap^0|1|A|I|4|1G|4|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

When <code>FileWriter</code> creates a new <code>File</code> object internally, this is not what causes the file to come into existence. That happens in other parts of the code. A <code>File</code> object is just a standard way to designate a file (or directory), whether or not it exists.

blocks|key|1922512|text|确实有很多原因，但是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1922513|文件被java.io中的许多类使用。FileReader，等等。FileWriter是一个使用文件的“方便”类，它使程序员更有效率。一些类只需要一个指向文件位置的File对象，然后根据需要对其进行操作以支持其处理。其他类可能支持FileWriter，因为它只会写入文件，而不会读取。它还使API具有更强的类型。|1922514|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

There are lots of reasons really, but:

File is used by many classes in java.io. FileReader, etc... FileWriter is a "convenience" class that uses File and it enables the programmer to be more productive. Some Classes just want a File object which points to a file location and then they operate on it as needed to support their processing. Other Classes might support a FileWriter because it will only be writing to a file and not reading. It also makes the API more strongly-typed.

blocks|key|2614231|text|我认为file.createNewFile()在实际中创建了新文件。请参阅下面的detal代码。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2614232|++File+file+=+new+File("D:\\tables\\test.sql");

++++++++++++//+if+file+does+not+exists,+then+create+it
++++++++++++if+(!file.exists())+{
++++++++++++++++file.createNewFile();
++++++++++++}

++++++++++++FileWriter+fw+=+new+FileWriter(file.getAbsoluteFile());|code-block|syntax|javascript|2614233|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I think file.createNewFile() creates the new file in actual.. please see following code for detal...

<pre><code> File file = new File("D:\\tables\\test.sql");

 // if file does not exists, then create it
 if (!file.exists()) {
 file.createNewFile();
 }

 FileWriter fw = new FileWriter(file.getAbsoluteFile());
</code></pre>

<code>new File("abc.txt")</code> does not create actual file while <code>new FileWriter("abc.txt")</code> creates a file on disk. While going through source code i found that <code>new FileWriter("abc.txt")</code> eventually creates an object of file like <code>new File()</code>

why new FileWriter("abc.txt") creates a new file and new File("abc.txt") does not?

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。

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new FileWriter("abc.txt")在磁盘上创建文件时，new File("abc.txt")不会创建实际的文件。在浏览源代码时，我发现new FileWriter("abc.txt")最终创建了一个类似于new File()的文件对象

问为什么新文件(“abc.txt”)会创建一个新文件，而新文件(“abc.txt”)不会？
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问为什么新文件(“abc.txt”)会创建一个新文件，而新文件(“abc.txt”)不会？EN