Do Java arrays have a maximum size

Question

Is there a limit to the number of elements a Java array can contain  If so  what is it

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This is  of course  totally VM-dependent   Browsing through the source code of OpenJDK 7 and 8 java util ArrayList   Hashtable   AbstractCollection    PriorityQueue  and  Vector  you can see this claim being repeated           Some VMs reserve some header words in an array     Attempts to allocate larger arrays may result in    OutOfMemoryError  Requested array size exceeds VM limit     private static final int MAX ARRAY SIZE   Integer MAX VALUE - 8     which is added by Martin Buchholz  Google  on 2010-05-09  reviewed by Chris Hegarty  Oracle    So   probably  we can say that the maximum  safe  number would be  2 147 483 639  Integer MAX VALUE - 8  and  attempts to allocate larger arrays may result in OutOfMemoryError     Yes  Buchholz s standalone claim does not include backing evidence  so this is a calculated appeal to authority  Even within OpenJDK itself  we can see code like return  minCapacity  gt  MAX ARRAY SIZE    Integer MAX VALUE   MAX ARRAY SIZE  which shows that MAX ARRAY SIZE does not yet have a real use

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I tried to create a byte array like this  byte   bytes   new byte Integer MAX VALUE-x   System out println bytes length     With this run configuration   -Xms4G -Xmx4G   And java version      Openjdk version  1 8 0 141        OpenJDK Runtime Environment  build 1 8 0 141-b16        OpenJDK 64-Bit Server VM  build 25 141-b16  mixed mode    It only works for x    2 which means the maximum size of an array is Integer MAX VALUE-2  Values above that give     Exception in thread  main  java lang OutOfMemoryError  Requested array size exceeds VM limit       at Main main Main java 6

User · Answer

Yes  there limit on java array  Java uses an integer as an index to the array and the maximum integer store by JVM is 2 32  so you can store 2 147 483 647 elements in the array    In case you need more than max-length you can use two different arrays but the recommended method is store data into a file  because storing data in the file has no limit  because files stored in your storage drivers but array are stored in JVM  JVM provides limited space for program execution

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Actually it s java limitation caping it at 2 30-4 being 1073741820  Not 2 31-1  Dunno why but i tested it manually on jdk  2 30-3 still throwing vm except  Edit  fixed -1 to -4  checked on windows jvm

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Arrays are non-negative integer indexed   so maximum array size you can access would be Integer MAX VALUE  The other thing is how big array you can create  It depends on the maximum memory available to your JVM and the content type of the array  Each array element has it s size  example  byte   1 byte  int   4 bytes  Object reference   4 bytes  on a 32 bit system    So if you have 1 MB memory available on your machine  you could allocate an array of byte 1024   1024  or Object 256   1024     Answering your question - You can allocate an array of size  maximum available memory   size of array item       Summary - Theoretically the maximum size of an array will be Integer MAX VALUE  Practically it depends on how much memory your JVM has and how much of that has already been allocated to other objects

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Going by this article http   en wikipedia org wiki Criticism of Java Large arrays      Java has been criticized for not supporting arrays of more than 231-1  about 2 1 billion  elements  This is a limitation of the language  the Java Language Specification  Section 10 4  states that            Arrays must be indexed by int values    An attempt to access an array     component with a long index value results in a compile-time error       Supporting large arrays would also require changes to the JVM  This limitation manifests itself in areas such as collections being limited to 2 billion elements and the inability to memory map files larger than 2 GiB  Java also lacks true multidimensional arrays  contiguously allocated single blocks of memory accessed by a single indirection   which limits performance for scientific and technical computing

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Haven t seen the right answer  even though it s very easy to test   In a recent HotSpot VM  the correct answer is Integer MAX VALUE - 5   Once you go beyond that   public class Foo     public static void main String   args        Object   array   new Object Integer MAX VALUE - 4           You get   Exception in thread  main  java lang OutOfMemoryError    Requested array size exceeds VM limit

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Maximum number of elements of an array is  2 31 -1 or 2 147 483 647

User · Answer

There are actually two limits   One  the maximum element indexable for the array and  two  the amount of memory available to your application   Depending on the amount of memory available and the amount used by other data structures  you may hit the memory limit before you reach the maximum addressable array element

[java] Do Java arrays have a maximum size?

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