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POWeird: can not change the value of Integer in jni
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10650230
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10663966
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2
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6
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2012-05-18T09:41:10.480
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2012-05-22T03:00:08.103
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2012-05-22T03:00:08.103
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I write a jni function to set the value of two java Integer object in C, just like this: <pre><code>jni_do_something(JNIEnv *env, jobject thiz, jobject p1, jobject p2) { jclass c; jfieldID id; c = env->FindClass("java/lang/Integer"); if (c==NULL) { LOGD("FindClass failed"); return -1; } id = env->GetFieldID(c, "value", "I"); if (id==NULL) { LOGD("GetFiledID failed"); return -1; } env->SetIntField(p1, id, 5); env->SetIntField(p2, id, 10); return 0; } </code></pre> In java, I called this function: <pre><code>native int do_something(Integer p1, Integer p2); Integer p1=0, p2=0; do_something(p1, p2); Log.d("test", "p1: "+p1); Log.d("test", "p2: "+p2); </code></pre> The output are both '10', why? =============================================== I have done many tests, and got the following points. (Answer, comments are welcome) <ol> <li>I don't think this jni native is unable to alter immutable object. After all, the both objects are changed to 10 from 0.</li> <li>There is some relation to auto-boxing (yes? I'm not sure). Maybe p1 and p2 are specially processed by jvm, made pointed to a single object if initialized with: Integer p1=0, p2=0;</li> </ol> If change to: <pre><code>Integer p1=0, p2=1; </code></pre> or <pre><code>Integer p1 = new Integer(0); Integer p2 = new Integer(0); </code></pre> The result is right (p1:5, p2:10). Can anyone clarify this? Maybe what I said is not correct. I have write the following code in java: <pre><code>Integer a = 0; Integer b = 0; b = 10; Log.d("test", "a: "+a); Log.d("test", "b: "+b); </code></pre> It output 0, 10. So, they point to not a single object. I'm really confused.
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<android><jni>
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Weird: can not change the value of Integer in jni
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