Re: hashmap serialize

From:
Lew <lew@lewscanon.nospam>
Newsgroups:
comp.lang.java.help
Date:
Tue, 31 Jul 2007 19:59:25 -0400
Message-ID:
<bZqdnUUNNMBAUTLbnZ2dnUVZ_qy3nZ2d@comcast.com>
gg wrote:

I am using jdk 1.6 and thought serializing hashmap would be a cinch

I got


There is no "class" declaration (e.g., "public class RegexTest{").

    HashMap<String, RegexRecord> myRegexHolder;

There is no "import" declaration for java.util.HashMap.

    String sRegexHolderFile = "c:\data\.regexHolderObj.ser";

    if ( (new java.io.File(strRegexHolderObjFSpec)).exists()) {
            // restore myRegexHolder previously serialized
            boolean bFailed = false;

What's with the "b" prefix? The declaration "boolean" already makes it clear
that it's a boolean.

            try {
                // read and deserialize the blob
                FileInputStream fileIn = new
FileInputStream(strRegexHolderObjFSpec);
                ObjectInputStream ois = new ObjectInputStream(fileIn);
                myRegexHolder = (HashMap<String, regextest.RegexRecord>)
ois.readObject();
// oops Got warning: D:\proj\Util\RegexTest\src\regextest\RegexTest.java:55:
warning: [unchecked] unchecked cast

You really can't cast generically, it's one of Java's little eccentricities.

                //myRegexHolder = myRegexHolder.readObject(ois);

I'm pretty sure that uncommenting this line would give an access violation for
the attempt to invoke a private method of myRegexHolder.

                ois.close();
            } catch (ClassNotFoundException ex) {
                setStatus("Exception in deSerializing myRegexHolder: " +
ex.getMessage());
                ex.printStackTrace();
                bFailed = true;
            } catch (IOException ex) {
                setStatus("Exception in deSerializing myRegexHolder - IO
error: " + ex.getMessage());
                ex.printStackTrace();
                bFailed = true;
            }

            if ( bFailed == false)


What's the problem with saying "if ( ! bFailed )"?

 setStatus("restore myRegexHolder successfully from user file");
        } else {
            // create empty myRegexHolder
            myRegexHolder = new HashMap<String, RegexRecord>(180,
(float)0.75);

Ooh, magic numbers!
Seriously, how did you arrive at these values?

            setStatus("Created myRegexHolder successfully for initial
capacity of 180 and 75% load factor");
        };
    }

...... some processing that results adding, updating the hsahmap of
myRegexHolder
.... before closing or at user request save the hashmap\ to external file

These lines won't compile.

 private void saveRegexHolder() {

    //serialize myRegexHolder
        myRegexHolder.writeToObject();
// oops , error: D:\proj\Util\RegexTest\src\regextest\RegexTest.java:499:
cannot find symbol


You should copy and paste the exact error message instead of paraphrashing.
Cannot find /what/ symbol?

 )

......

This line will not compile.

}

please help, thank you for your time and effort


Several issues:

You did not provide a compilable example. You've been around this group long
enough to have heard of an SSCCE:
<http://www.physci.org/codes/sscce.html>
They really do help.

You called writeToObject(), not writeObject(java.io.ObjectOutputStream).
First, HashMap has no method writeToObject(); it makes no sense to call
methods that don't exist. Second, writeObject() is a private method; you
cannot call it from an instance of a different class.

In the line:

String sRegexHolderFile = "c:\data\.regexHolderObj.ser";


you neglected to escape the backslashes. The actual string in
sRegexHolderFile (why the useless leading 's'?) will contain no path separator
characters. To get a backslash into a String you need to double it:
  String sRegexHolderFile = "c:\\data\\.regexHolderObj.ser";

You will be unable to locate the file with the unescaped backslashes. Check out
<http://java.sun.com/docs/books/tutorial/java/nutsandbolts/datatypes.html>

Happy to help.

--
Lew

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