Plz help , getting error in my java code

Question

Can any one tell the reason for this error:
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
is there any size limit for java classes that I am using in my code?
My code Looks like:
     FileChannel in = null, out = null;
     try {
     in = new FileInputStream(sourceLocation).getChannel();
System.out.println(in.size() +"RptPageBreak rtn: b 4 read file into buffer, source=" + sourceLocation);
// read the file into buffer
// System.out.println("-1 " +in.size() );
MappedByteBuffer buf = in.map(FileChannel.MapMode.READ_ONLY, 0, in.size());
     //System.out.println("RptPageBreak rtn: AFTER read file into buffer" );
System.out.println("1: "+ buf.capacity()+" " +in.size() );
// CharBuffer cb;
               try {
                    cb = Charset.forName ("UTF-8").decode (buf);
               } catch (Exception ex) {
                    System.out.println("2:"+ ex.getMessage());
                    ex.printStackTrace();
System.out.println("2");
String lines[] = Pattern.compile ("\n").split (cb, 0);
     //System.out.println("RptPageBreak rtn: lines.len=" + lines.length);
     Writer writer = new FileWriter (targetLocation);
     System.out.println("3");
     for (int i = 0, n = lines.length; i < n; i++) {
          // also compare if starts with a CRLF
     if ( ( lines.startsWith("\r\n" + rpt_headg_id) == true ) ||
               ( lines[i].startsWith("\f" + rpt_headg_id) == true ) ||
( lines[i].startsWith(rpt_headg_id) == true ) )
//if ( lines[i].contains(rpt_headg_id) == true )
     //System.out.println("RptPageBreak rtn: found headg in if loop " + rpt_headg_id );
writer.write ("1");
else {
     writer.write (" "); // detail lines shift over 1 by addg a space
writer.write (lines[i]);
writer.write ('\n');
//System.out.println("RptPageBreak rtn: lines[i]=" + i + ' ' + lines[i]);
writer.close ();
}catch(Exception e)
     System.out.println("RptPageBreak rtn: Catch Exception: " + e.getMessage() );
     status=false;
e.printStackTrace();
finally {
     try {
if (in != null) in.close();
if (out != null) out.close();
status=true;
catch(Exception e)
     System.out.println("RptPageBreak rtn: Finally-Catch Exception: " + e.getMessage() );
     status=false;
e.printStackTrace();

Answer 1

It has nothing to do with classes. It is that you are reading to much info into memory at one time. If you are only going to cycle through the input line for line, anyway, then why don't you simply read the file (or whatever) a line at a time and process it as you read it, rather than loading the entire thing at once?