与原始`int`相比，使用原始`byte'增加了占用的空间

Question

I have a sample program for which I'm testing the memory occupied. I don't know where I'm going wrong or I'm implementing something wrong. But when I use byte instead of int , memory occupied by JVM is increased. Below are two class files:

Class Test1:

public class Test1 {
    public Test1 node1, node2;
    DATATYPE a, b; // DATATYPE is Primitive `int` or Primitive `byte`
}

Class Test:

public class Test {
    public static void main(String args[]) throws IOException
    {
        System.out.println(getMemory());

        Test1 root = new Test1();
        Test1 currNode = root;
        for(int i = 0; i < 10000000; i++)
        {
            currNode.node1 = new Test1();
            currNode.a = 10;
            currNode.b = 10;
            currNode.node2 = currNode;
            currNode = new Test1();
        }

        System.out.println(getMemory());
    }

public static String getMemory()
    {
        HashMap<String, Double> hm = new HashMap<String, Double>();
        Runtime runtime = Runtime.getRuntime();
        hm.put("\nTotal Memory ", (double) runtime.totalMemory()/(1024*1024));
        hm.put("\nFree Memory ", (double) runtime.freeMemory()/(1024*1024));
        hm.put("\nUsedup Memory ", (double) (runtime.totalMemory() - runtime.freeMemory())/(1024*1024));
        return hm.toString();
    }
}

Output1 when DATATYPE = int:

{
    Free Memory = 966.1398086547852, 
    Total Memory = 981.5, 
    Usedup Memory = 15.360191345214844}
{
    Free Memory = 869.7226409912109, 
    Total Memory = 981.5, 
    Usedup Memory = 111.77735900878906
}

Output1 when DATATYPE = byte:

{
    Free Memory = 966.1398086547852, 
    Total Memory = 981.5, 
    Usedup Memory = 15.360191345214844
}
{
    Free Memory = 765.0790710449219, 
    Total Memory = 981.5, 
    Usedup Memory = 216.42092895507812
}

I don't know if I'm doing something wrong. What could be the reason for this?

Answer 1

Byte is a boxed primitive which requires more memory than primitives such as int, double, etc.

Object references such as boxed primitives (eg Byte, Integer, Double) have additional overhead such as a Class reference.

Therefore using byte instead of Byte should resolve your issue.