blocks|key|514840|text|如果不可能经常发生更改，那么设置布尔变量的每次更改开销也是可以忽略不计的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|514841|理想情况下，您的代码中有一个点，即所有更改都必须通过(例如，处理撤销/重做的地方)，并且可以将布尔变量更新代码放在那里。|514842|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|$]]

If changes aren't likely to happen often then surely the per-change overhead of setting a boolean variable is negligible too.

Ideally you'll have a point in your code that all changes have to go through (for example where you deal with undo/redo) and you can put your boolean variable updating code there.

blocks|key|306159|text|另一种方法是读取文件并对照程序的内容检查它的内容，这似乎会产生不必要的开销。或者节省保存某些内容的时间，并检查自那以后是否进行了更改。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|306160|考虑到我认为你的布尔解是目前为止最有效的。|306161|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|$]]

The alternative would be to read the file and check it´s contents against the content of your program, which seems to produce unnecessary overhead. Or to save the time when something has been saved and check if changes has been made since. 

Considering that I think your boolean solution is by far the most efficient.

blocks|key|514863|text|我的建议是使FileWriter类记住文件的状态(保存/更改)，因此您只需要使用这个编写器，并且不需要每次写入文件时都处理布尔操作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|514864|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|$]]

My propose is to make FileWriter class which remember the state of file (saved / changed) so you only need to use this writer and don't need to deal with boolean operations every time you write to file.

blocks|key|306020|text|如果文档不是很大，您可以在后台将其副本与用户可以编辑的文档分开保存，然后在应用程序关闭之前对两者进行比较。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|306021|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|$]]

If the document isn't really big, you could keep a copy of it behind the scenes separate from the one the user can edit, and then just compare the two before the app closes.

blocks|key|516427|text|布尔变量是最好的主意。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|516428|boolean+isDataChanged|code-block|syntax|javascript|516429|这是一个很好的阅读，并没有混淆代码。|516430|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

A boolean variable is a the best Idea.

<pre><code>boolean isDataChanged
</code></pre>

It is nice to read, and does not confuse the code.

blocks|key|516432|text|我刚刚在google上为你找到了这个小的二进制比较方法，没有承诺如果它工作的话;)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|516433|/**
*+Compare+binary+files.+Both+files+must+be+files+(not+directories)+and+exist.
*+
*+@param+first++-+first+file
*+@param+second+-+second+file
*+@return+boolean+-+true+if+files+are+binery+equal
*+@throws+IOException+-+error+in+function
*/
public+boolean+isFileBinaryEqual(
++File+first,
++File+second
)+throws+IOException
{
++//+TODO:+Test:+Missing+test
++boolean+retval+=+false;

++if+((first.exists())+&&+(second.exists())+
+++++&&+(first.isFile())+&&+(second.isFile()))
++{
+++++if+(first.getCanonicalPath().equals(second.getCanonicalPath()))
+++++{
++++++++retval+=+true;
+++++}
+++++else
+++++{
++++++++FileInputStream+firstInput+=+null;
++++++++FileInputStream+secondInput+=+null;
++++++++BufferedInputStream+bufFirstInput+=+null;
++++++++BufferedInputStream+bufSecondInput+=+null;

++++++++try
++++++++{++++++++++++
+++++++++++firstInput+=+new+FileInputStream(first);+
+++++++++++secondInput+=+new+FileInputStream(second);
+++++++++++bufFirstInput+=+new+BufferedInputStream(firstInput,+BUFFER_SIZE);+
+++++++++++bufSecondInput+=+new+BufferedInputStream(secondInput,+BUFFER_SIZE);

+++++++++++int+firstByte;
+++++++++++int+secondByte;

+++++++++++while+(true)
+++++++++++{
++++++++++++++firstByte+=+bufFirstInput.read();
++++++++++++++secondByte+=+bufSecondInput.read();
++++++++++++++if+(firstByte+!=+secondByte)
++++++++++++++{
+++++++++++++++++break;
++++++++++++++}
++++++++++++++if+((firstByte+<+0)+&&+(secondByte+<+0))
++++++++++++++{
+++++++++++++++++retval+=+true;
+++++++++++++++++break;
++++++++++++++}
+++++++++++}
++++++++}
++++++++finally
++++++++{
+++++++++++try
+++++++++++{
++++++++++++++if+(bufFirstInput+!=+null)
++++++++++++++{
+++++++++++++++++bufFirstInput.close();
++++++++++++++}
+++++++++++}
+++++++++++finally
+++++++++++{
++++++++++++++if+(bufSecondInput+!=+null)
++++++++++++++{
+++++++++++++++++bufSecondInput.close();
++++++++++++++}
+++++++++++}
++++++++}
+++++}
++}

++return+retval;
}|code-block|syntax|javascript|516434|来源：http://www.java2s.com/Code/Java/File-Input-Output/Comparebinaryfiles.htm|offset|length|516435|当您想要保存您的文件时，只需创建currentFile的file，并将其与您现有的文件进行比较;)|516436|entityMap|0|LINK|mutability|MUTABLE|url|http://www.java2s.com/Code/Java/File-Input-Output/Comparebinaryfiles.htm^0|0|0|3|20|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@$I|X|J|Y|1|Z]]|A|$]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

I just found this little bit binary compare method for you on google, no promise if it works ;) 

<pre><code>/**
* Compare binary files. Both files must be files (not directories) and exist.
* 
* @param first - first file
* @param second - second file
* @return boolean - true if files are binery equal
* @throws IOException - error in function
*/
public boolean isFileBinaryEqual(
 File first,
 File second
) throws IOException
{
 // TODO: Test: Missing test
 boolean retval = false;

 if ((first.exists()) &amp;&amp; (second.exists()) 
 &amp;&amp; (first.isFile()) &amp;&amp; (second.isFile()))
 {
 if (first.getCanonicalPath().equals(second.getCanonicalPath()))
 {
 retval = true;
 }
 else
 {
 FileInputStream firstInput = null;
 FileInputStream secondInput = null;
 BufferedInputStream bufFirstInput = null;
 BufferedInputStream bufSecondInput = null;

 try
 { 
 firstInput = new FileInputStream(first); 
 secondInput = new FileInputStream(second);
 bufFirstInput = new BufferedInputStream(firstInput, BUFFER_SIZE); 
 bufSecondInput = new BufferedInputStream(secondInput, BUFFER_SIZE);

 int firstByte;
 int secondByte;

 while (true)
 {
 firstByte = bufFirstInput.read();
 secondByte = bufSecondInput.read();
 if (firstByte != secondByte)
 {
 break;
 }
 if ((firstByte &lt; 0) &amp;&amp; (secondByte &lt; 0))
 {
 retval = true;
 break;
 }
 }
 }
 finally
 {
 try
 {
 if (bufFirstInput != null)
 {
 bufFirstInput.close();
 }
 }
 finally
 {
 if (bufSecondInput != null)
 {
 bufSecondInput.close();
 }
 }
 }
 }
 }

 return retval;
}
</code></pre>

source: <a href="http://www.java2s.com/Code/Java/File-Input-Output/Comparebinaryfiles.htm" rel="nofollow">http://www.java2s.com/Code/Java/File-Input-Output/Comparebinaryfiles.htm</a>

you just have to create an File object of your currentFile, when you want to save your file, and compare it to you´r existing File ;)

I have an app that may save some files. When the user closes the app, I would like to ask for saving if the user did not already save the file as it is currenty. 
If I am not clear enough, I somehow want to check if the file has been modified from the last saving. 
I have considered making a <code>Boolean</code> variable that turns to <code>true</code> if the file is saved and then turns back to <code>false</code> every time the file is modified in any way (writing or deleting elements in the file). 
My question is if there is any easier solution to do that. It seems to me a lot of useless work to set the variable to <code>true</code> every time the file changes (work both for me and the machine), and I would not want this, since I have a quite wide and complex app, and changes in file are likely to happen quite often. 

Edit after the answers:
Thank you all, it was really helpful. Eventually I realised that I needed a function that was needed in most of the changes I made to the file, so I didn't need to work so much. The other changes were not so many so I just made the changes to the <code>Boolean</code>. 
Thanks again

Check if file was already saved java

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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我有一个应用程序，可以保存一些文件。当用户关闭应用程序时，如果用户还没有保存当前的文件，我想请求保存。如果我不够清楚，我想要检查文件是否从上次保存中修改过。我已经考虑过创建一个Boolean变量，如果保存了该文件，该变量将转到true，然后每次以任何方式修改该文件时(写入或删除文件中的元素)都会返回到false。我的问题是，是否有更容易的解决办法来做到这一点。在我看来，每次文件更改时都要将变量设置

问检查文件是否已经保存了java
EN

回答 6

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问检查文件是否已经保存了javaEN

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问检查文件是否已经保存了java
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