Is it possible to get the size of the Vector or ArrayList or any object for that matter in bytes in java? size() function gives only the number of elements. But I want to get the actual size of the object.
For the time being, I implemented my own for getting size.
long sizeof(ArrayList<String> list)
{
long size = 0;
for(String s: list)
size+=s.length();
return size;
}
Different JDK having different size for the implicite objects.
You can count it by implicite object size multiply the length of the vector or arraylist. For Example if you declare a araylist of integer with 10 records in it, then Java integers are 32 bits ie 32/8 = 4 bytes. You have 10 records hence 10x4 = 40 byetes.
in standard java byte = 8 bits, short=16bits, int=32bits, long=64bits.
First : try to read Does Java have an operator like "sizeof()" in C
Second : Try this code :
public class Sizeof
{
public static void main (String [] args) throws Exception
{
// Warm up all classes/methods we will use
runGC ();
usedMemory ();
// Array to keep strong references to allocated objects
final int count = 100000;
Object [] objects = new Object [count];
long heap1 = 0;
// Allocate count+1 objects, discard the first one
for (int i = -1; i < count; ++ i)
{
Object object = null;
// Instantiate your data here and assign it to object
object = new Object ();
//object = new Integer (i);
//object = new Long (i);
//object = new String ();
//object = new byte [128][3]
if (i >= 0)
objects [i] = object;
else
{
object = null; // Discard the warm up object
runGC ();
heap1 = usedMemory (); // Take a before heap snapshot
}
}
runGC ();
long heap2 = usedMemory (); // Take an after heap snapshot:
final int size = Math.round (((float)(heap2 - heap1))/count);
System.out.println ("'before' heap: " + heap1 +
", 'after' heap: " + heap2);
System.out.println ("heap delta: " + (heap2 - heap1) +
", {" + objects [0].getClass () + "} size = " + size + " bytes");
for (int i = 0; i < count; ++ i) objects [i] = null;
objects = null;
}
private static void runGC () throws Exception
{
// It helps to call Runtime.gc()
// using several method calls:
for (int r = 0; r < 4; ++ r) _runGC ();
}
private static void _runGC () throws Exception
{
long usedMem1 = usedMemory (), usedMem2 = Long.MAX_VALUE;
for (int i = 0; (usedMem1 < usedMem2) && (i < 500); ++ i)
{
s_runtime.runFinalization ();
s_runtime.gc ();
Thread.currentThread ().yield ();
usedMem2 = usedMem1;
usedMem1 = usedMemory ();
}
}
private static long usedMemory ()
{
return s_runtime.totalMemory () - s_runtime.freeMemory ();
}
private static final Runtime s_runtime = Runtime.getRuntime ();
} // End of class
This is supposed to show memory usage
Runtime rt = Runtime.getRuntime();
long m0 = rt.totalMemory() - rt.freeMemory();
Object obj = new Object(); // create your object here
long m1 = rt.totalMemory() - rt.freeMemory();
System.out.println(m1 - m0);
but it does not work. This works (at least on my PC)
public static void main(String[] args) throws Exception {
Object obj = createObject();
long m0 = usedMem();
long m1 = usedMem();
obj = null;
for (int i = 0; i < 100; i++)
System.gc();
m0 = usedMem();
obj = createObject();
for (int i = 0; i < 100; i++)
System.gc();
m1 = usedMem();
System.out.println(m1 - m0);
}
private static long usedMem() {
return Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory();
}
private static Object createObject() {
return new Object();
}
if it prints 8
for new Object and 40
for new String() then it works correctly, then create your object and see its size
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