コード

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;

public class ObjectUtils {
	public static int getObjectSize(Object o) {
		ObjectOutput out = null;
		try (ByteArrayOutputStream bos = new ByteArrayOutputStream()) {
			out = new ObjectOutputStream(bos);
			out.writeObject(o);
			out.flush();
			byte[] b = bos.toByteArray();
			return b.length;
		} catch (IOException e) {
			return -1;
		}
	}
}

使い方

	public static void main(String[] args) {
		{
			String o = "ABC";
			System.err.println(ObjectUtils.getObjectSize(o));
		}
		{
			Integer o = 100;
			System.err.println(ObjectUtils.getObjectSize(o));
		}
		{
			String[] o = { "ABC", "ABC", "ABC" };
			System.err.println(ObjectUtils.getObjectSize(o));
		}
	}

実行結果例

10
81
60