how to increase java heap memory permanently?

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The Java Virtual Machine takes two command line arguments which set the initial and maximum heap sizes: -Xms and -Xmx. You can add a system environment variable named _JAVA_OPTIONS, and set the heap size values there.
For example if you want a 512Mb initial and 1024Mb maximum heap size you could use:

under Windows:

SET _JAVA_OPTIONS = -Xms512m -Xmx1024m

under Linux:

export _JAVA_OPTIONS="-Xms512m -Xmx1024m"

It is possible to read the default JVM heap size programmatically by using totalMemory() method of Runtime class. Use following code to read JVM heap size.

public class GetHeapSize {
    public static void main(String[]args){

        //Get the jvm heap size.
        long heapSize = Runtime.getRuntime().totalMemory();

        //Print the jvm heap size.
        System.out.println("Heap Size = " + heapSize);
    }
}

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