Android NDK Practical Learning (quad)-Class cache

1, why class caching is required:

A: Because it takes a lot of time and space overhead to find classes and class member variables frequently, you can refer to the following articles:

http://www.ibm.com/developerworks/cn/java/j-jni/

Http://www.28im.com/java/a2379737.html

2, the cache needs to use static in the Java class, as follows:

1  PackageCom.dasea.test.core;2  Public classTestsetdata {3     //mainly the class ID and the field ID, the method ID of the cache4     Static {5 onnative ();6     }7 8      Public native Static voidonnative ();9 Ten      Public Booleanbdata; One      Public DoubleDData; A      Public intIData; -      Public byteCData; -      PublicString SData; the      Public bytebytearr[]; -  -      Public intintarr[]; -  +      PublicTestsetdata () { -         //TODO auto-generated Constructor stub +Bdata =true; ADData = 100.11; atIData = 333; -CData = 100; -SData = "20150204"; -Bytearr =New byte[10]; -          for(inti = 0; i < bytearr.length; i++) { -Bytearr[i] = ' 2 '; in         } -  toIntarr =New int[10]; +          for(inti = 0; i < intarr.length; i++) { -Intarr[i] = i * 10; the         } *     } $}

The relevant implementation code for the 3,c++ side:

① defines a corresponding structure:

1 struct jtestsetdata{  2    jclass   jtestsetdata; 3 4     jfieldid jbdata; 5     jfieldid jidata; 6     jfieldid jddata; 7     jfieldid jcdata; 8     jfieldid jsdata; 9     jfieldid jarrdata; Ten };

② defines the variables for the corresponding class:

struct Jtestsetdata Gs_testsetdatamgr;

③ Implement the Cache function:

 1  jniexport void   Jnicall java_com_dasea_test_core_testsetdata_onnative ( 2  Jnienv*
   
     env, Jobject obj) { 
    3  debug_out (
     " 
    testsetdata native start!  
     " 
        4   Inittestsetdata (env);  6   " testsetdata native end!   "  8 } 
   

1 BOOLInittestsetdata (jnienv*env) {2     //cache classes and their fields3     //find the field inside the class and assign the value4 5     //STEP 1/3: Load the class ID6Jclass jcsetdatamgr = Env->findclass ("Com/kq/rtk/core/testsetdata");7 8     //STEP 2/3: Assign the ClassId as a Global Reference9Gs_testsetdatamgr.jtestsetdata = (jclass) env->Newglobalref (jcsetdatamgr);Ten  OneJfieldid Funb = Env->getfieldid (Jcsetdatamgr,"bdata","Z"); AGs_testsetdatamgr.jbdata =Funb; -Gs_testsetdatamgr.jidata = Env->getfieldid (Jcsetdatamgr,"IData","I"); -Gs_testsetdatamgr.jddata = Env->getfieldid (Jcsetdatamgr,"DData","D"); theGs_testsetdatamgr.jcdata = Env->getfieldid (Jcsetdatamgr,"CData","B"); -Gs_testsetdatamgr.jsdata = Env->getfieldid (Jcsetdatamgr,"SData","ljava/lang/string;"); -Gs_testsetdatamgr.jarrdata = Env->getfieldid (Jcsetdatamgr,"Intarr","[I"); -  +     //STEP 3/3: Delete the no longer needed local reference -Env->Deletelocalref (jcsetdatamgr); +  A     return true; at}

④ using cached classes and members:

Java-side interface:

 Public native void testprecachefun (Testsetdata obj);

C + + Side implementation:

1JniexportvoidJnicall Java_com_dasea_test_core_rtknativemanager_testprecachefun (2jnienv*env, Jobject obj, Jobject jobj) {3Debug_out ("Testprecache start!");4 5     if(NULL = =gs_testsetdatamgr.jtestsetdata) {6Debug_out ("No Cache class!");7         if(false==Inittestsetdata (env)) {8Debug_out ("Cache failed!");9             return ;Ten         } OneDebug_out ("Cache success!"); A}Else{ -Debug_out ("Has cache!"); -     } the  -Env->setbooleanfield (Jobj, Gs_testsetdatamgr.jbdata,false); -Env->setdoublefield (Jobj, Gs_testsetdatamgr.jddata,209.22); -Env->setintfield (Jobj, Gs_testsetdatamgr.jidata,3653); +Env->setbytefield (Jobj, Gs_testsetdatamgr.jcdata, the); -  +Debug_out ("Set Field succ!"); A  at     Chardata[Ten] ="JFKDSAJFL"; -Jstring SSS = env->Newstringutf (data); -Env->Setobjectfield (jobj, Gs_testsetdatamgr.jsdata, SSS); -Env->Deletelocalref (SSS); -  -     //gets the object of the array property arrays in Java inJintarray Jint_arr = (jintarray) env->Getobjectfield (Jobj, gs_testsetdatamgr.jarrdata); -     intarrint[Ten] = {0}; to      for(inti =0; I <Ten; ++i) { +Arrint[i] = -+i; -     } theEnv->setintarrayregion (Jint_arr,0,Ten, arrint); *  $Debug_out ("Testprecache end!");Panax Notoginseng}

⑤ constructs a class object using a cache class:

1      Debug_out ("allocobject Object! " ); 2      " <init> " " () V " ); 3      Jobject Jresult = Env->newobject (Gs_testgetdatamgr.jtestgetdata, Initid);

Android NDK Practical Learning (quad)-Class cache