How to find Heap size in Java

Java objects reside in a memory area called the heap. It is possible to know the memory specifications of heap in a Java program. In this blog, I’ll demonstrate how to find heap size in Java using the java.lang.Runtime class.

java.lang.Runtime class has the following 3 methods which can give information about the heap memory size:

• totalMemory() – Returns the total amount of memory in the Java virtual machine.
• maxMemory() – Returns the maximum amount of memory that the Java virtual machine will attempt to use.
• freeMemory() – Returns the amount of free memory in the Java Virtual Machine.

public class HeapSizeDemo
{
	public static void main(String[] args)
	{
		java.io.PrintStream out = System.out;

		// Get an instance of the Runtime class
		Runtime runtime = Runtime.getRuntime();

		// To convert from Bytes to MegaBytes:
		// 1 MB = 1024 KB and 1 KB = 1024 Bytes.
		// Therefore, 1 MB = 1024 * 1024 Bytes.
		long MegaBytes = 1024 * 1024;

		// Memory which is currently available for use by heap
		long totalMemory = runtime.totalMemory() / MegaBytes;
		out.println("Heap size available for use -> " + totalMemory + " MB");

		// Maximum memory which can be used if required.
		// The heap cannot grow beyond this size
		long maxMemory = runtime.maxMemory() / MegaBytes;
		out.println("Maximum memory Heap can use -> " + maxMemory + " MB");

		// Free memory still available
		long freeMemory = runtime.freeMemory() / MegaBytes;
		out.println("Free memory in heap -> " + freeMemory + " MB");

		// Memory currently used by heap
		long memoryInUse = totalMemory - freeMemory;
		out.println("Memory already used by heap -> " + memoryInUse + " MB");
	}
}

A sample output of the above program is shown below