Is there any sizeof-like method in Java

Question

Is there any built-in method in Java to find the size of any datatype  Is there any way to find size

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yes  in JAVA  System out println Integer SIZE 8      gives you 4  System out println Integer SIZE       gives you 32     Similary for Byte Long Double

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The Java Native Access library is typically used for calling native shared libraries from Java   Within this library there exist methods for determining the size of Java objects   The getNativeSize Class cls  method and its overloads will provide the size for most classes   Alternatively  if your classes inherit from JNA s Structure class the calculateSize boolean force  method will be available

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The Instrumentation class has a getObjectSize   method however  you shouldn t need to use it at runtime   The easiest way to examine memory usage is to use a profiler which is designed to help you track memory usage

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EhCache provides a SizeOf class that will try to use the Instrumentation agent and will fall back to a different approach if the agent is not loaded or cannot be loaded  details here     Also see the agent from Heinz Kabutz

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No   There is no such method in the standard Java SE class library  The designers  view is that it is not needed in Java  since the language removes the need for an application1 to know about how much space needs to be reserved for a primitive value  an object or an array with a given number of elements  You might think that a sizeof operator would be useful for people that need to know how much space their data structures take   However you can also get this information and more  simply and reliably using a Java memory profiler  so there is no need for a sizeof method   Previous commenters made the point that sizeof someType  would be more readable than 4   If you accept that readability argument  then the remedy is in your hands   Simply define a class like this     public class PrimitiveSizes       public static int sizeof byte b    return 1         public static int sizeof short s    return 2           etcetera        and statically import it     import static PrimitiveSizes     Or define some named constants  e g  public static final int SIZE OF INT   4   Or  Java 8 and later  use the Integer BYTES constant  and so on   Why haven t the Java designers implemented this in standard libraries   My guess is that   they don t think there is a need for it  they don t think there is sufficient demand for it  and they don t think it is worth the effort   There is also the issue that the next demand would be for a sizeof Object o  method  which is fraught with technical difficulties  The key word in the above is  quot they quot    1 - A programmer may need to know in order to design space efficient data structures   However  I can t imagine why that information would be needed in application code at runtime via a method call

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From the article in JavaWorld     A superficial answer is that Java does not provide anything like C s sizeof    However     let s consider why a Java programmer might occasionally want it       A C programmer manages most datastructure memory allocations himself    and sizeof   is indispensable for knowing memory block sizes to   allocate  Additionally  C memory allocators like malloc   do almost   nothing as far as object initialization is concerned  a programmer   must set all object fields that are pointers to further objects  But   when all is said and coded  C C   memory allocation is quite   efficient       By comparison  Java object allocation and construction are tied   together  it is impossible to use an allocated but uninitialized   object instance   If a Java class defines fields that are references   to further objects  it is also common to set them at construction   time  Allocating a Java object therefore frequently allocates numerous   interconnected object instances  an object graph  Coupled with   automatic garbage collection  this is all too convenient and can make   you feel like you never have to worry about Java memory allocation   details       Of course  this works only for simple Java applications  Compared with   C C    equivalent Java datastructures tend to occupy more physical   memory  In enterprise software development  getting close to the   maximum available virtual memory on today s 32-bit JVMs is a common   scalability constraint  Thus  a Java programmer could benefit from   sizeof   or something similar to keep an eye on whether his   datastructures are getting too large or contain memory bottlenecks    Fortunately  Java reflection allows you to write such a tool quite   easily       Before proceeding  I will dispense with some frequent but incorrect   answers to this article s question  Fallacy  Sizeof   is not needed   because Java basic types  sizes are fixed      Yes  a Java int is 32 bits in all JVMs and on all platforms  but this   is only a language specification requirement for the   programmer-perceivable width of this data type  Such an int is   essentially an abstract data type and can be backed up by  say  a   64-bit physical memory word on a 64-bit machine  The same goes for   nonprimitive types  the Java language specification says nothing about   how class fields should be aligned in physical memory or that an array   of booleans couldn t be implemented as a compact bitvector inside the   JVM  Fallacy  You can measure an object s size by serializing it into   a byte stream and looking at the resulting stream length      The reason this does not work is because the serialization layout is   only a remote reflection of the true in-memory layout  One easy way to   see it is by looking at how Strings get serialized  in memory every   char is at least 2 bytes  but in serialized form Strings are UTF-8   encoded and so any ASCII content takes half as much space

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There s a class jar available on SourceForge net that uses Java instrumentation to calculate the size of any object  Here s a link to the description  java sizeOf

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You can use Integer SIZE   8  Double SIZE   8  etc  for primitive types from Java 1 5

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Just some testing about it  public class PrimitiveTypesV2    public static void main  String   args        Class typesList                   Boolean class   Byte class  Character class  Short class  Integer class              Long class  Float class  Double class  Boolean TYPE  Byte TYPE  Character TYPE              Short TYPE  Integer TYPE  Long TYPE  Float TYPE  Double TYPE                     try                          for   Class type   typesList                 if  type isPrimitive                      System out println  quot Primitive type  t quot    type                              else                   boolean hasSize   false                  java lang reflect Field fields     type getFields                    for  int count 0  count lt fields length  count                          if  fields count  getName   contains  quot SIZE quot    hasSize   true                                    if  hasSize                        System out println  quot Bits size of type  quot    type    quot    t t t quot    type getField  quot SIZE quot   getInt type                         double value   type getField  quot MIN VALUE quot   getDouble type                       long longVal   Math round value                       if    value - longVal     0                            System out println  quot Min value for type  quot    type    quot    t t quot    longVal                            longVal   Math round type getField  quot MAX VALUE quot   getDouble type                            System out println  quot Max value for type  quot    type    quot    t t quot    longVal                                              else                           System out println  quot Min value for type  quot    type    quot    t t quot    value                            value   type getField  quot MAX VALUE quot   getDouble type                           System out println  quot Max value for type  quot    type    quot    t t quot    value                                                            else                       System out println type    quot  t t t type without SIZE field  quot                                       if not primitive              for typesList       catch  Exception e   e printStackTrace          main      class PrimitiveTypes

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I don t think it is in the java API  but most datatypes which have a number of elements in it  have a size   method  I think you can easily write a function to check for size yourself

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There is a contemporary way to do that for primitives  Use BYTES of types   System out println  byte     Byte BYTES   System out println  char     Character BYTES   System out println  int     Integer BYTES   System out println  long     Long BYTES   System out println  short     Short BYTES   System out println  double     Double BYTES   System out println  float     Float BYTES     It results in   byte 1 char 2 int 4 long 8 short 2 double 8 float 4

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You can do bit manipulations like below to obtain the size of primitives   public int sizeofInt         int i   1  j   0      while  i    0            i    i lt  lt 1   j              return j     public int sizeofChar         char i   1  j   0      while  i    0            i    char   i lt  lt 1   j              return j

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As mentioned here  there are possibilities to get the size of primitive types through their wrappers    e g  for a long this could be Long SIZE   Byte SIZE from java 1 5  as mentioned by zeodtr already  or Long BYTES as from java 8

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I decided to create an enum without following the standard Java conventions  Perhaps you like this   public enum sizeof             public static final int FLOAT   Float SIZE   8      public static final int INTEGER   Integer SIZE   8      public static final int DOUBLE   Double SIZE   8

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Try java lang Instrumentation getObjectSize Object   But please be aware that     It returns an implementation-specific approximation of the amount of storage consumed by the specified object  The result may include some or all of the object s overhead  and thus is useful for comparison within an implementation but not between implementations  The estimate may change during a single invocation of the JVM

[java] Is there any sizeof-like method in Java?

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