什么是 native 对象意味着我发现 java 具有与 native 对象交互的对等类?
最佳答案
Java程序可以使用JNI访问以 native 代码实现的功能(任何编译为机器代码的东西)。与面向对象的 native 代码接口(interface)需要一个 java 类,它使用 jni 将方法调用从 java 转发到 native 类的实例。此类是 native 类的 java 对等体。
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,为此我们需要在 java 中定义它的对等体。
原生类
class print_hello{
public:
void do_stuff(){std::cout<<"hello"<<std::endl;}
}
java中的peer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)
所有声明为 native
的方法都需要一个本地 jni 实现。以下仅实现上面声明的 native 方法之一。
//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();
}
关于java - 什么是本地对象?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/4568972/