What is the default heap size in a oc4j instance

Hi There,
I am wondering what is the default heap size for an oc4j instance if you don't specify -Xms and -Xmx?
Thanks,
Xingsheng

If you're using the Sun JDK 1.4 I believe the max is 64MB. Not sure about 5.0. It's really dependent on the JVM you're using, not OC4J.
Jason

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Overriding the default heap size of 64mb

I run the java program on my pc on windows xp
I need to increase the heap size, currently I launch the jar file using a batch file, the contents of the batch file are:
java -Xms64m -Xmx512m -jar Lines.jar
I have set the min and max heap size and when I click on the .bat file it launches the jar file with tose heap settings
But I do not want to launch the jar file in this way(I don't want to use a batch file), is there anyway to override the default heap size for the java program to 512mb so that every time I launch the jar file the heap size is 512mb??
Edited by: muddy777 on Sep 23, 2009 6:30 PM

Vikash.SunJava wrote:
set this in some machine startup like a scheduled task at machine startup
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This this will be default JVM settings.Huh?

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If we dont specify what is the default buffer size in BufferedWriter. How to increase/decrease the size of it?
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THis is the bufferedwriter class, it helps to look at them, look at the bold underlined, thats answers your defualt buffer size
* @(#)BufferedWriter.java 1.26 03/12/19
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
package java.io;
* Write text to a character-output stream, buffering characters so as to
* provide for the efficient writing of single characters, arrays, and strings.
* The buffer size may be specified, or the default size may be accepted.
* The default is large enough for most purposes.
* A newLine() method is provided, which uses the platform's own notion of
* line separator as defined by the system property <tt>line.separator</tt>.
* Not all platforms use the newline character ('\n') to terminate lines.
* Calling this method to terminate each output line is therefore preferred to
* writing a newline character directly.
* In general, a Writer sends its output immediately to the underlying
* character or byte stream. Unless prompt output is required, it is advisable
* to wrap a BufferedWriter around any Writer whose write() operations may be
* costly, such as FileWriters and OutputStreamWriters. For example,
* <pre>
* PrintWriter out
* = new PrintWriter(new BufferedWriter(new FileWriter("foo.out")));
* </pre>
* will buffer the PrintWriter's output to the file. Without buffering, each
* invocation of a print() method would cause characters to be converted into
* bytes that would then be written immediately to the file, which can be very
* inefficient.
* @see PrintWriter
* @see FileWriter
* @see OutputStreamWriter
* @version 1.26, 03/12/19
* @author Mark Reinhold
* @since JDK1.1
public class BufferedWriter extends Writer {
private Writer out;
private char cb[];
private int nChars, nextChar;
private static int defaultCharBufferSize = 8192;
* Line separator string. This is the value of the line.separator
* property at the moment that the stream was created.
private String lineSeparator;
* Create a buffered character-output stream that uses a default-sized
* output buffer.
* @param out A Writer
*public BufferedWriter(Writer out) {*
* this(out, defaultCharBufferSize);*
* Create a new buffered character-output stream that uses an output
* buffer of the given size.
* @param out A Writer
* @param sz Output-buffer size, a positive integer
* @exception IllegalArgumentException If sz is <= 0
public BufferedWriter(Writer out, int sz) {
 super(out);
 if (sz <= 0)
 throw new IllegalArgumentException("Buffer size <= 0");
 this.out = out;
 cb = new char[sz];
 nChars = sz;
 nextChar = 0;
 lineSeparator = (String) java.security.AccessController.doPrivileged(
new sun.security.action.GetPropertyAction("line.separator"));
/** Check to make sure that the stream has not been closed */
private void ensureOpen() throws IOException {
 if (out == null)
 throw new IOException("Stream closed");
* Flush the output buffer to the underlying character stream, without
* flushing the stream itself. This method is non-private only so that it
* may be invoked by PrintStream.
void flushBuffer() throws IOException {
 synchronized (lock) {
 ensureOpen();
 if (nextChar == 0)
 return;
 out.write(cb, 0, nextChar);
 nextChar = 0;
* Write a single character.
* @exception IOException If an I/O error occurs
public void write(int c) throws IOException {
 synchronized (lock) {
 ensureOpen();
 if (nextChar >= nChars)
 flushBuffer();
 cb[nextChar++] = (char) c;
* Our own little min method, to avoid loading java.lang.Math if we've run
* out of file descriptors and we're trying to print a stack trace.
private int min(int a, int b) {
 if (a < b) return a;
 return b;
* Write a portion of an array of characters.
* Ordinarily this method stores characters from the given array into
* this stream's buffer, flushing the buffer to the underlying stream as
* needed. If the requested length is at least as large as the buffer,
* however, then this method will flush the buffer and write the characters
* directly to the underlying stream. Thus redundant
* <code>BufferedWriter</code>s will not copy data unnecessarily.
* @param cbuf A character array
* @param off Offset from which to start reading characters
* @param len Number of characters to write
* @exception IOException If an I/O error occurs
public void write(char cbuf[], int off, int len) throws IOException {
 synchronized (lock) {
 ensureOpen();
if ((off < 0) || (off > cbuf.length) || (len < 0) ||
((off + len) > cbuf.length) || ((off + len) < 0)) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return;
 if (len >= nChars) {
 /* If the request length exceeds the size of the output buffer,
 flush the buffer and then write the data directly. In this
 way buffered streams will cascade harmlessly. */
 flushBuffer();
 out.write(cbuf, off, len);
 return;
 int b = off, t = off + len;
 while (b < t) {
 int d = min(nChars - nextChar, t - b);
 System.arraycopy(cbuf, b, cb, nextChar, d);
 b += d;
 nextChar += d;
 if (nextChar >= nChars)
 flushBuffer();
* Write a portion of a String.
* If the value of the <tt>len</tt> parameter is negative then no
* characters are written. This is contrary to the specification of this
* method in the {@linkplain java.io.Writer#write(java.lang.String,int,int)
* superclass}, which requires that an {@link IndexOutOfBoundsException} be
* thrown.
* @param s String to be written
* @param off Offset from which to start reading characters
* @param len Number of characters to be written
* @exception IOException If an I/O error occurs
public void write(String s, int off, int len) throws IOException {
 synchronized (lock) {
 ensureOpen();
 int b = off, t = off + len;
 while (b < t) {
 int d = min(nChars - nextChar, t - b);
 s.getChars(b, b + d, cb, nextChar);
 b += d;
 nextChar += d;
 if (nextChar >= nChars)
 flushBuffer();
* Write a line separator. The line separator string is defined by the
* system property <tt>line.separator</tt>, and is not necessarily a single
* newline ('\n') character.
* @exception IOException If an I/O error occurs
public void newLine() throws IOException {
 write(lineSeparator);
* Flush the stream.
* @exception IOException If an I/O error occurs
public void flush() throws IOException {
 synchronized (lock) {
 flushBuffer();
 out.flush();
* Close the stream.
* @exception IOException If an I/O error occurs
public void close() throws IOException {
 synchronized (lock) {
 if (out == null)
 return;
 flushBuffer();
 out.close();
 out = null;
 cb = null;
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Example, you have a file called c, your writer is b and buffereredwriter is a. so your programs calls a, a talks to b, and b talks to c. when you call the Flush method, the information is sent to the outfile which is c immediately before you even close the file, because when you write to the file, it does not write directly, it writes to a buffer, so flush actually causes the buffer to write to file. Also if you call the close method on that file without the flush, the buffer will still get flushed.
consider BufferedWriter c = new BufferedWriter(new PrintWriter("c:\\c"));
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Dear all,
Please tell me what is the default heap memory size when we start the jvm (using the java command) ?

Google ( [sun java default heap size|http://www.google.com/search?q=sun+java+default+heap+size] )

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Edited by: 938864 on Jun 5, 2012 11:16 PM

938864 wrote:
Hi Kayaman,
Sorry but I don't agree with you on verification part, Why not I can verify it ? to me default means value when I don't specify -Xms and -Xmx and by the way I was testing that program on 32 bit JRE 1.6 on Windows. I am also curious significant difference between 128MB and 870MB I saw, do you see anything obviously wrong ?That spec is outdated. Since Java 6 update 18 (Sun/Oracle implementation) the default maximum heap space is calculated based on total memory availability, but never more than 1GB on 32 bits JVMs / client VMs. On a 64 bits server VM the default can go as high as 32gb.
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All,
Please help!!
I have tested my Application Client Project in WSAD on my pc and it works fine.
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-? -help print this help message
-X print help on non-standard options
Could not create the Java virtual machine.
Press any key to continue . . .
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@echo off
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@pause
I have changed the value of Xms and Xmx of JVM_ARGS to different size but I sitll get error. Anyone knows what the problem is. Thanks..

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What is the default heap size in a oc4j instance

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