什么是原生对象？ [英] what is a native object?

问题描述

什么是本机对象意味着我发现java具有与本机objets接口的对等类？

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

推荐答案

Java程序可以使用 JNI 访问以本机代码实现的功能（任何内容）编译成机器代码）。与面向对象的本机代码接口需要一个java类，它使用jni将方法调用从java转发到本机类的实例。这个类是本机类的java对等。

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.

一个例子：
我们在c ++中有print_hello类，我们需要在java程序中使用它，要做到这一点，我们需要在java中定义它的对等。

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.

原生类

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

java中的对等类

  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代码（不完整）

所有方法声明 native 需要本机jni实现。以下仅实现了上面声明的一个本机方法。

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();
} 

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