Developers Arena: JVM Heap Size

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How to get JVM heap size, used memory, total memory using Java Runtime

Java’s Runtime class provide lot of information about the resource  details of Java Virtual Machine or JVM. The memory consumed by the JVM  can be read by different methods in Runtime class.

Following is the small example of getting/reading JVM Heap Size, Total Memory and used memory using Java Runtime api.

public class Memoryusage{
 
    public static void main(String [] args) {
 
        int mb = 1024*1024;
 
        //Getting the runtime reference from system
        Runtime runtime = Runtime.getRuntime();
 
        System.out.println("Heap Space usage in MB");
 
        //Print used memory
        System.out.println("Used Memory:"
            + (runtime.totalMemory() - runtime.freeMemory()) / mb);
 
        //Print free memory
        System.out.println("Free Memory:"
            + runtime.freeMemory() / mb);
 
        //Print total available memory
        System.out.println("Total Memory:" + runtime.totalMemory() / mb);
 
        //Print Maximum available memory
        System.out.println("Max Memory:" + runtime.maxMemory() / mb);
    }

Increase heap size in Java to prevent java.lang.OutOfMemoryError

Setting/Increase JVM heap size

It is possible to increase heap size allocated by the Java Virtual Machine (JVM) by using command line options.
Following are few options available to change Heap Size.

-Xms<size>        set initial Java heap size
-Xmx<size>        set maximum Java heap size
-Xss<size>        set java thread stack size

What is Java Heap Space in Java virtual Machine JVM?

Java heap is the heap size allocated to JVM applications which takes care of the new objects being created. If the objects being created exceed the heap size, it will throw an error saying memoryOutof Bound
Java's default heap size limit is 128MB.
It is possible to increase heap size allocated by the Java Virtual Machine (JVM) by using command line options.
Following are few options available to change Heap Size.

-Xms        set initial Java heap size
-Xmx        set maximum Java heap size
-Xss        set java thread stack size

How do I increase the heap size available to Eclipse?

Some JVMs put restrictions on the total amount of memory available on the heap. If you are getting OutOfMemoryErrors while running Eclipse, the VM can be told to let the heap grow to a larger amount by passing the -vmargs command to the Eclipse launcher. For example, the following command would run Eclipse with a heap size of 256MB

eclipse [normal arguments] -vmargs -Xmx256M [more VM args]

The arguments after -vmargs are directly passed to the VM. Run java -X for the list of options your VM accepts. Options starting with -X are implementation-specific and may not be applicable to all VMs.
You can also put the extra options in eclipse.ini.
Here is an example;
-startup plugins/org.eclipse.equinox.launcher_1.0.100.v20080501.jar --launcher.library plugins/org.eclipse.equinox.launcher.gtk.linux.x86_64_1.0.100.v20080428-1330 -showsplash org.eclipse.platform -vm /usr/lib/jvm/java-1.5.0-sun/jre/bin/java -vmargs -Xms512m -Xmx1024m -XX:+UseParallelGC -XX:PermSize=256M -XX:MaxPermSize=512M

How to Increase JVM / Java Heap Size,Increasing JVM / Java Heap Size Tutorial

Java programs executes in JVM uses Heap of memory to manage the data. If your Java program requires a large amount of memory, it is possible that the virtual machine will begin to throw OutOfMemoryError instances when attempting to instantiate an object. The default heap size if 1 MB and can increase as much as 16 MB.

It is possible to increase heap size allocated by the Java Virtual Machine (JVM) by using command line options.
Following are few options available to change Heap Size.

-Xms<size>        set initial Java heap size
-Xmx<size>        set maximum Java heap size
-Xss<size>        set java thread stack size
 
Also we can set the Minimum and Maximum Heap size
 
java -Xms64m -Xmx256m MyProgram

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