java - How did JVM implement array's class? -

can override methods of array? example tostring() or other methods.

import java.lang.reflect.method;  public class arraysclasstest {   static int[] array = { 1, 2, 3, 1 };    public static void main(string[] args) {     class<? extends int[]> class1 = array.getclass();     try {         method method = class1.getmethod("tostring");     } catch (nosuchmethodexception | securityexception e) {         // todo auto-generated catch block         e.printstacktrace();     } } 

}

you can't change features of arrays. jls §10.7 array members specifies every member of array:

the members of array type of following:

• the public final field length, contains number of components of array. length may positive or zero.

• the public method clone, overrides method of same name in class object , throws no checked exceptions. return type of clone method of array type t[] t[].

  a clone of multidimensional array shallow, creates single new array. subarrays shared.

• all members inherited class object; method of object not inherited clone method.

the specification doesn't allow way of customizing implementation. array's tostring() method, example, basic 1 inherited object.

to create array object compiler emits 1 of 3 instructions compiled java bytecode: newarray primitives, anewarray reference types, or multinewarray multidimensional arrays. in implementing instructions, virtual machine creates each array class needed @ runtime (jvms §5.3.3 creating array classes). vm defines dedicated bytecode instructions compiler use getting , setting elements of arrays , getting array's length.

how arrays implemented within vm not specified whatsoever. purely implementation detail, , java compiler doesn't know, or care. actual code involved depends on flavor of virtual machine you're running program on, version of vm, os , cpu it's running on, , relevant runtime options vm configured (e.g., whether in interpreted mode or not).

a quick on openjdk 8 source code turns of relevant machinery arrays:

• src/share/vm/oops/arrayklass.cpp

• src/share/vm/oops/objarrayklass.cpp

• src/share/vm/oops/typearrayklass.cpp

• src/share/vm/interpreter/bytecodeinterpreter.cpp – implements bytecode instructions interpreter, including instructions creating , accessing arrays. it's tortuous , intricate, however.

• src/share/vm/c1/c1_rangecheckelimination.cpp – performs clever array bounds check eliminations when compiling bytecode native code.

as arrays core feature of language , vm, it's impossible point 1 source file , "here, class array code". arrays special, , machinery implements them literally on place.

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if want customize behavior of array, thing can not use array directly, use, subclass, or write, collection class internally contains array. gives complete freedom define class's behavior , performance characteristics. however, impossible make custom class be array in java language sense. means can't make implement [] operator or passable method expects array.