Java中类型与C/C++中对应关系

 

Java中的类的对应

 

Sign签名, 用来识别对应各个方法。

JDK下的javap.exe能输出签名。用法javap -s -p 完整类名

 

 

 package com.test;

 import java.util.Date;

 public class TestNative {

     public native void sayHello();

     private int a = 10;

     public int function(int x,Date date,int[] y){

         System.out.println("function");

         return 0;

     }

     public double max(double a,double b){

         return a>b?a:b;

     }

     /**

      * @param args

      */

     public static void main(String[] args) {

         System.loadLibrary("NativeCode");

         TestNative tNative = new TestNative();

         tNative.sayHello();

     }

 }

 #include<iostream.h>

 #include"com_test_TestNative.h"

 JNIEXPORT void JNICALL Java_com_test_TestNative_sayHello(JNIEnv *env, jobject obj)

 {

     //因为sayHello不是静态函数，所以传进来的obj就是调用这个函数的对象，否则就是传入native方法所在的类

     jclass hello_clazz = env->GetObjectClass(obj); //得到的就是native方法所在的类

 //    jfieldID fieldId_a = env->GetFieldID(hello_clazz,"a","I");

 //    jmethodID methodId_fun = env->GetMethodID(hello_clazz,"function","(ILjava/util/Date;[I)I");

 //    env->CallIntMethod(obj,methodId_fun,0L,NULL,NULL); //方法调用

 //    cout<<"hello world!"<<endl;

 //    cout<<"successful"<<endl;

 /*

     jfieldID field_a = env->GetFieldID(hello_clazz,"a","I");  //得到字段a的ID

     jint a = env->GetIntField(obj,field_a);   //得到字段a的值

     cout<<a<<endl;

     env->SetIntField(obj,field_a,100L);

 */

     jmethodID methodId_max = env->GetMethodID(hello_clazz,"max","(DD)D");

     jvalue *values = new jvalue[];  //jvalue是用来向java函数中传参数的

     values[].d = 3.14;

     values[].d = 3.22;

     //jdouble max = env->CallDoubleMethod(obj,methodId_max,3.18,3.15); //第一种方法调用

     jdouble max = env->CallDoubleMethodA(obj,methodId_max,values); //第二种方法调用

     delete [] values;

     cout<<max<<endl;

 }

 package com.test;

 import java.io.BufferedReader;

 import java.io.IOException;

 import java.io.InputStreamReader;

 public class TestStr {

     public native void cppCode();

     private String message;

     public static void main(String[] args) throws IOException {

         System.loadLibrary("CPP");

         BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

         String str = reader.readLine();

         TestStr obj = new TestStr();

         obj.message = str;

         obj.cppCode();

         System.out.println("java :"+obj.message);

     }

 }

 #include "com_test_TestStr.h"

 #include<windows.h>

 #include<string>

 #include<algorithm>

 using namespace std;

 JNIEXPORT void JNICALL Java_com_test_TestStr_cppCode(JNIEnv *env, jobject obj)

 {

     jfieldID fid_msg = env->GetFieldID(env->GetObjectClass(obj),"message","Ljava/lang/String;");

     jstring j_msg = (jstring)env->GetObjectField(obj,fid_msg);

     jsize len = env->GetStringLength(j_msg);   //得到字符串的长度

     jchar* jstr = new jchar[len+];    //申请空间

     jstr[len] = L'\0';

     env->GetStringRegion(j_msg,,len,jstr);

     //env->ReleaseStringChars(j_msg,jstr);

     //MessageBoxW(NULL,(const wchar_t*)jstr,L"Title",MB_OK);

     wstring wstr((const wchar_t*)jstr);

     delete[] jstr;  //释放空间

     std::reverse(wstr.begin(),wstr.end());  //字符串反转

     jstring j_new_str = env->NewString((const jchar*)wstr.c_str(),(jint)wstr.size());   //创建一个新的字符串

     env->SetObjectField(obj,fid_msg,j_new_str);  //设置字符串给java对象

 }

 package com.test;

 public class TestArray {

     public int[] array = {,,,,,,,,,};

     public native void callCppFun();

     public static void main(String[] args) {

         System.loadLibrary("TestArray");

         TestArray obj = new TestArray();

         obj.callCppFun();

         for(int a:obj.array){

             System.out.println(a);

         }

     }

 }

 #include"com_test_TestArray.h"

 #include<iostream>

 #include<algorithm>

 using namespace std;

 JNIEXPORT void JNICALL Java_com_test_TestArray_callCppFun (JNIEnv *env, jobject obj)

 {

     jfieldID fid_array = env->GetFieldID(env->GetObjectClass(obj),"array","[I"); //获取数组的id

     jintArray jint_array = (jintArray)env->GetObjectField(obj,fid_array);   

     jint* int_arr = env->GetIntArrayElements(jint_array,NULL); //转化为jint数组

     jsize len = env->GetArrayLength(jint_array);

     std::sort(int_arr,int_arr+len);  //对数组进行排序

     env->ReleaseIntArrayElements(jint_array,int_arr,); //0：释放C++数组，并且更新到Java

 /*    for(jsize i=0;i<len;i++){

         cout<<int_arr[i]<<endl;

     }

 */

  //   env->ReleaseIntArrayElements(jint_array,int_arr,JNI_ABORT);//JNI_ABORT:释放C++数组，但是不更新到Java

 }