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javaterminology
satheesh.droid
satheesh.droid

Reputation: 31517

what is a native object?

what is a native object means i found the that java has peer class to interface with native objets?

Upvotes: 11

Views: 9796

Answers (2)

josefx
josefx

Reputation: 15656

Java programs can use JNI to access to functions implemented in native code (anything compiled to machine code). Interfacing with object oriented native code requires a java class which forwards method calls from java to an instance of the native class using jni. This class is the java peer of the native class.

An example: We have the print_hello class in c++ which we need to use in a java program, to do this we need to define its peer in java.

The native class 

  class print_hello{
  public:
      void do_stuff(){std::cout<<"hello"<<std::endl;}
  }

The peer class in java

  class PrintHello{
    //Address of the native instance (the native object)
    long pointer;

    //ctor. calls native method to create
    //instance of print_hello
    PrintHello(){pointer = newNative();}

    ////////////////////////////
    //This whole class is for the following method
    //which provides access to the functionality 
    //of the native class
    public void doStuff(){do_stuff(pointer);}

    //Calls a jni wrapper for print_hello.do_stuff()
    //has to pass the address of the instance.
    //the native keyword keeps the compiler from 
    //complaining about the missing method body
    private native void do_stuff(long p);

    //
    //Methods for management of native resources.
    //

    //Native instance creation/destruction
    private native long newNative();
    private native deleteNative(long p);

    //Method for manual disposal of native resources
    public void dispose(){deleteNative(pointer);pointer = 0;}
  }

JNI code (incomplete)

All methods declared native require a native jni implementation. The following implements only one of the native methods declared above.

//the method name is generated by the javah tool
//and is required for jni to identify it.
void JNIEXPORT Java_PrintHello_do_stuff(JNIEnv* e,jobject i, jlong pointer){
    print_hello* printer = (print_hello*)pointer;
    printer->do_stuff();
}

Upvotes: 20

Peter Lawrey
Peter Lawrey

Reputation: 533530

A Java object has a peer/native object if it has some native methods written in C.

Upvotes: 1

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