Calculate card input memory

Question

I have a map (String, String), and I want to find the size of memory for the record and the map as a whole. I read somewhere that Instrumentation can be useful ( Instrumentation ). Anyone have an idea?

Thanks in advance.

Answer 1

An empty java.util.AbstractMap.SimpleEntry instance should be 24 bytes for a 64-bit JVM and 12 bytes for a 32-bit JVM. Here is the @PeterLawrey technique that I found useful, based on a MemoryUsageExamplesTest :

 System.out.printf("The average memory used by simple entry is %.1f bytes%n", new SizeofUtil() { @Override protected int create() { Map.Entry<String, String> e = new AbstractMap.SimpleEntry<String, String>(null, null); return 1; } }.averageBytes()); 

Answer 2

Use ObjectOutputStream to write an object to ByteArrayOutputstream and check the length of the resulting byte array.

Obviously, your Map.Entry will need to implement Serializable.

 public int getSizeInBytes(Serializable someObject) { ByteArrayOutputStream byteOut = new ByteArrayOutputStream(); ObjectOutputStream objectOut = new ObjectOutputStream(byteOut); objectOut.writeObject(someObject); objectOut.flush(); return byteOut.toByteArray().length; } public int getSizeBits(Serializable someObject) { return getSizeInBytes(someObject) * 8; }