Map占用內存大小評估

public class test {
    private static java.util.HashMap<String, String> needQueryResProductList = new java.util.HashMap<String, String>();
    public static void main(String[] args) throws Exception {

        String userlabel="12345678998765432100";
        long start = 0;
        long end = 0;
        // 先垃圾回收
        System.gc();
        start = Runtime.getRuntime().freeMemory();
        HashMap map = new HashMap();
        for (int i = 0; i < 360000; i++) {
            map.put("1111,2222,3333"+String.valueOf(i), userlabel);
        }
        // 快要計算的時,再清理一次
        System.gc();
        end = Runtime.getRuntime().freeMemory();
        System.out.println("一個HashMap對象占內存:" + (end - start));
}
}