Javaのメモリ使用量(64bitマシン)の計算するプログラムを書きました。プリミティブなフィールドのみに対応します。"gen_nomethod_class.py"はテスト用のクラスの生成のために使っています。

gen_no_method_class.py

#!/usr/bin/env python2.7
#encoding:utf-8
import random
def gen():
  fmt = """public class %(CLASS)s {
    public boolean   %(BOOLEAN)s;
    public int       %(INT)s;
    public char      %(CHAR)s;
    public long      %(LONG)s;
    public double    %(DOUBLE)s;
    public boolean[] %(BI)s;
    public char[]    %(AC)s;
    public int[]     %(AI)s;
    public long[]    %(LI)s;
    public double[]  %(DI)s;
  }"""
  for i in range(4):
    class_name = "NoMethodClass%d" % i
    b = ["b%d" % d for d in range(random.randint(1, 4))]
    c = ["c%d" % d for d in range(random.randint(1, 4))]
    i = ["i%d" % d for d in range(random.randint(1, 4))]
    do = ["d%d" % d for d in range(random.randint(1, 4))]
    l = ["l%d" % d for d in range(random.randint(1, 4))]
    bi = "bi = new boolean[%d]" % pow(2, random.randint(3, 10))
    ac = "ci = new char[%d]" % pow(2, random.randint(3, 10))
    ai = "ai = new int[%d]" % pow(2, random.randint(3, 10))
    li = "li = new long[%d]" % pow(2, random.randint(3, 10))
    di = "di = new double[%d]" % pow(2, random.randint(3, 10))
    with open("%s.java" % class_name,"w") as f:
      f.write(fmt % {
        "CLASS":class_name,
        "BOOLEAN": ",".join(b), 
        "CHAR": ",".join(c), 
        "INT": ",".join(i),
        "LONG": ",".join(l),
        "DOUBLE": ",".join(do),
        "BI": bi,
        "AC": ac,
        "AI": ai,
        "LI": li,
        "DI": di
      })
gen()

MemoryCheck.java

import java.lang.reflect.Field;
public class MemoryCheck {
  private static int OVERHEAD = 16;
  public static int calcUsage(Class testClass) throws Exception {
    int usage = OVERHEAD;
      Object obj = testClass.newInstance();
      for (Field field : testClass.getDeclaredFields()) {
        String fieldName = field.getName();
        String fieldType = field.getType().getSimpleName();
        if (fieldType.equals("boolean"))
          usage += 1;
        else if  (fieldType.equals("char"))
          usage += 2;
        else if  (fieldType.equals("int"))
          usage += 4;
        else if  (fieldType.equals("long"))
          usage += 8;
        else if  (fieldType.equals("double")) 
          usage += 8;
        else if  (fieldType.equals("boolean[]")) {
          usage += 8; // ref
          int n = ((boolean[]) field.get(obj)).length;
          usage += 1 * n + 24;
        }
        else if  (fieldType.equals("char[]")) {
          usage += 8; // ref
          int n = ((char[]) field.get(obj)).length;
          usage += 2 * n + 24;
        }
        else if  (fieldType.equals("int[]")) {
          usage += 8; // ref
          int n = ((int[]) field.get(obj)).length;
          usage += 4 * n + 24;
        }
        else if  (fieldType.equals("long[]")) {
          usage += 8; // ref
          int n = ((long[]) field.get(obj)).length;
          usage += 8 * n + 24;
        }
        else if  (fieldType.equals("double[]")) {
          usage += 8; // ref
          int n = ((double[]) field.get(obj)).length;
          usage += 8 * n + 24;
        }
        else {
          throw new Exception(fieldType);
        }
       }
       while (usage % 8 != 0) usage++; // padding
       return usage;
  }
  public static void main(String[] args) throws Exception {
    if (args.length != 1) throw new IllegalArgumentException();
     int usage = calcUsage(Class.forName(args[0]));
     System.out.println("usage = " + usage + " bytes");
  }
}

Test_MemoryCheck.java

import junit.framework.TestCase;

public class Test_MemoryCheck extends TestCase {
    public void testTestClass0() {
    try {
      assertEquals(1992, MemoryCheck.calcUsage(Class.forName("NoMethodClass0")));
      } catch(Exception e) {
        fail(e.getMessage());
      }
    }
    public void testTestClass1() {
      try {
      assertEquals(8912, MemoryCheck.calcUsage(NoMethodClass1.class));
      } catch(Exception e) {
        fail(e.getMessage());
      }
    }
    public void testTestClass2() {
      try {
      assertEquals(6720, MemoryCheck.calcUsage(NoMethodClass2.class));
      } catch(Exception e) {
        fail(e.getMessage());
      }
    }
    public void testTestClass3() {
      try {
      assertEquals(10056, MemoryCheck.calcUsage(NoMethodClass3.class));
      } catch(Exception e) {
        fail(e.getMessage());
      }
    }
}