what is a native object?

what is a native object means i found 开发者_如何学编程the that java has peer class to interface with native objets?

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();
} 

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