How is length implemented in Java Arrays

Question

I was wondering about the implementation of length of a Java Array  I know that using arrayName length gives us the number of elements in the array  but was wondering if this is a method   function or it is just a data member of Array   I guess it must be a data member as we do not use parenthesis   when invoking it  But if it is a data member how when is the value of this length assigned computed

User · Answer

I believe its just a property as you access it as a property.

String[] s = new String[]{"abc","def","ghi"}
System.out.println(s.length)

returns 3

if it was a method then you would call s.length() right?

User · Answer

Java arrays  like C   arrays  have the fixed length that after initializing it  you cannot change it  But  like class template vector - vector  lt T gt  - in C   you can use Java class ArrayList that has many more utilities than Java arrays have

User · Answer

You re correct  length is a data member  not a method   From the Arrays tutorial      The length of an array is established when the array is created  After creation  its length is fixed

User · Answer

From the JLS      The array s length is available as a   final instance variable length   And      Once an array object is created  its   length never changes  To make an array   variable refer to an array of   different length  a reference to a   different array must be assigned to   the variable    And arrays are implemented in the JVM   You may want to look at the VM Spec for more info

User · Answer

If you have an array of a known type or is a subclass of Object   you can cast the array first   Object array   new      n   Object   array2    Object    array  System out println array2 length     or  Object array   new char n   char   array2    char    array  System out println array2 length     However if you have no idea what type of array it is you can use Array getLength Object    System out println Array getLength new boolean 4    System out println Array getLength new int 5    System out println Array getLength new String 6

User · Answer

According to the Java Language Specification  specifically   10 7 Array Members  it is a field         The public final field length  which contains the number of components of the array  length may be positive or zero        Internally the value is probably stored somewhere in the object header  but that is an implementation detail and depends on the concrete JVM implementation   The HotSpot VM  the one in the popular Oracle  formerly Sun  JRE JDK  stores the size in the object-header            arrays have a third header field  for the array size

User · Answer

Every array in java is considered as an object  The public final length is the data member which contains the number of components of the array  length may be positive or zero

User · Answer

Yes  it should be a field  And I think this value is assigned when you create your array  you have to choose the length of array while creating  for example  int   a   new int 5

User · Answer

It is a public final field for the array type  You can refer to the document below   http   java sun com docs books jls third edition html arrays html 10 7

[java] How is length implemented in Java Arrays?

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