Question

我想计算两个指向相同文本的字符串对象使用的内存。由于两个String都从以下结果指向相同的地址，因此我预计GraphLayout.parseInstance（text1，text2）.toFootprint（）中使用的总内存应为40（char []）+ 24（String类型）= 64字节。）。但是，将一个额外的24个String类型的字节添加到此总数中。还是我错过了一些不应以这种方式使用API的东西？

PrintWriter pw = new PrintWriter(out);
String text1 = "1111111111";
String text2 = "1111111111";

pw.println(GraphLayout.parseInstance(text1).toPrintable());
pw.println(GraphLayout.parseInstance(text2).toPrintable());
pw.println(GraphLayout.parseInstance(text1, text2).toPrintable());
pw.println(GraphLayout.parseInstance(text1, text2).toFootprint());
pw.println(RamUsageEstimator.sizeOf(text1));
pw.close();

这是执行结果：

Both text1 and text2 share the same String as they are pointing to the same address.
java.lang.String@4f209819d object externals:
          ADDRESS       SIZE TYPE             PATH                           VALUE
        76c6675e0         24 java.lang.String                                (object)
        76c6675f8         40 [C               .value                         [1, 1, 1, 1, 1, 1, 1, 1, 1, 1]


java.lang.String@4f209819d object externals:
          ADDRESS       SIZE TYPE             PATH                           VALUE
        76c6675e0         24 java.lang.String                                (object)
        76c6675f8         40 [C               .value                         [1, 1, 1, 1, 1, 1, 1, 1, 1, 1]

The GraphLayout of both text1 and text2 shows there are only one String object.
java.lang.String@4f209819d, java.lang.String@4f209819d object externals:
          ADDRESS       SIZE TYPE             PATH                           VALUE
        76c6675e0         24 java.lang.String <r2>                           (object)
        76c6675f8         40 [C               <r1>.value                     [1, 1, 1, 1, 1, 1, 1, 1, 1, 1]

The GraphLayout of both text1 and text2 shows there are only one String object.
java.lang.String@4f209819d, java.lang.String@4f209819d footprint:
     COUNT       AVG       SUM   DESCRIPTION
         1        40        40   [C
         2        24        48   java.lang.String
         3                  88   (total)

Java jol用常量池计算总内存占用量不准确吗？

0 个答案: