Reading runtime information about Java is useful when your application is struggling to get resources. System Memory is one of the main resources that an application developer has to consider while managing the application. Hence sometimes it is beneficial to see what amount of memory your application using and what amount of free memory is in system.

Java’s Runtime class provides 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.

The following is a small example of getting/reading JVM Heap Size, Total Memory and used memory using Java Runtime API.

/**
* Class: TestMemory
* @author: Viral Patel
* @description: Prints JVM memory utilization statistics
*/
public class TestMemory {

	public static void main(String [] args) {

		int mb = 1024*1024;

		//Getting the runtime reference from system
		Runtime runtime = Runtime.getRuntime();

		System.out.println("##### Heap utilization statistics [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);
	}
}

You may also want to print the memory utilization in Kilobytes KBs. For that just assign 1024 value to the int variable mb.

From http://viralpatel.net/blogs