Java Object Layout
以下步驟是查看物件佔用記憶體大小(byte)。
下載jol-core.jar，點擊下圖方框的部分。
加入jol-core.jar
包裝類別的佔用記憶體大小
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import org.openjdk.jol.info.ClassLayout;
public class Test {
public static void main(String[] args) {
System.out.println(ClassLayout.parseInstance((byte)1).toPrintable()); // Byte
System.out.println(ClassLayout.parseInstance('a').toPrintable()); // Character
System.out.println(ClassLayout.parseInstance(1).toPrintable()); // Integer
System.out.println(ClassLayout.parseInstance(1L).toPrintable()); // Long
System.out.println(ClassLayout.parseInstance(1.0f).toPrintable()); // Float
System.out.println(ClassLayout.parseInstance(1.0).toPrintable()); // Double
}
}
=============Boolean===================
java.lang.Boolean object internals:
OFF SZ TYPE DESCRIPTION VALUE
0 8 (object header: mark) 0x0000000000000001 (non-biasable; age: 0)
8 4 (object header: class) 0x00006390
12 1 boolean Boolean.value true
13 3 (object alignment gap)
Instance size: 16 bytes
Space losses: 0 bytes internal + 3 bytes external = 3 bytes total
=============Character===================
java.lang.Character object internals:
OFF SZ TYPE DESCRIPTION VALUE
0 8 (object header: mark) 0x0000002d6b418f01 (hash: 0x2d6b418f; age: 0)
8 4 (object header: class) 0x00023288
12 2 char Character.value a
14 2 (object alignment gap)
Instance size: 16 bytes
Space losses: 0 bytes internal + 2 bytes external = 2 bytes total
=============Byte===================
java.lang.Byte object internals:
OFF SZ TYPE DESCRIPTION VALUE
0 8 (object header: mark) 0x00000033affdfa01 (hash: 0x33affdfa; age: 0)
8 4 (object header: class) 0x00033da8
12 1 byte Byte.value 1
13 3 (object alignment gap)
Instance size: 16 bytes
Space losses: 0 bytes internal + 3 bytes external = 3 bytes total
=============short===================
java.lang.Short object internals:
OFF SZ TYPE DESCRIPTION VALUE
0 8 (object header: mark) 0x0000007413b5b301 (hash: 0x7413b5b3; age: 0)
8 4 (object header: class) 0x00035c40
12 2 short Short.value 1
14 2 (object alignment gap)
Instance size: 16 bytes
Space losses: 0 bytes internal + 2 bytes external = 2 bytes total
=============Integer===================
java.lang.Integer object internals:
OFF SZ TYPE DESCRIPTION VALUE
0 8 (object header: mark) 0x00000063c12bbe01 (hash: 0x63c12bbe; age: 0)
8 4 (object header: class) 0x00026830
12 4 int Integer.value 1
Instance size: 16 bytes
Space losses: 0 bytes internal + 0 bytes external = 0 bytes total
=============Long===================
java.lang.Long object internals:
OFF SZ TYPE DESCRIPTION VALUE
0 8 (object header: mark) 0x0000001d9ff05801 (hash: 0x1d9ff058; age: 0)
8 4 (object header: class) 0x00037950
12 4 (alignment/padding gap)
16 8 long Long.value 1
Instance size: 24 bytes
Space losses: 4 bytes internal + 0 bytes external = 4 bytes total
=============Float===================
java.lang.Float object internals:
OFF SZ TYPE DESCRIPTION VALUE
0 8 (object header: mark) 0x0000000000000001 (non-biasable; age: 0)
8 4 (object header: class) 0x00031228
12 4 float Float.value 1.0
Instance size: 16 bytes
Space losses: 0 bytes internal + 0 bytes external = 0 bytes total
=============Double===================
java.lang.Double object internals:
OFF SZ TYPE DESCRIPTION VALUE
0 8 (object header: mark) 0x0000000000000001 (non-biasable; age: 0)
8 4 (object header: class) 0x00032820
12 4 (alignment/padding gap)
16 8 double Double.value 1.0
Instance size: 24 bytes
Space losses: 4 bytes internal + 0 bytes external = 4 bytes total