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Reference: the Java JNI to interact with CC ++ programming
AndroidStudio use JNI to achieve Log log , we implemented a simple Java调用C++的方法example, took in the realization of a more complex interaction of Java and C ++.
Java call C ++
In the definition of the native methods MainActivity.java addTest01, and invokes the method corresponding to the incoming values, as follows:
Java native-lib.cpp received in the incoming value, and conversion, the output value corresponding to the print log.
Output results are as follows:
It can be seen from the above output, java array in which a value has changed, because the memory address directly modify the values in the C ++ as follows:
C ++ calling Java
We define a Student class, attribute values corresponding to the print process in the set, and defines a static method myStaticMethod, as follows:
Methods test03 method set to Student's age and name attribute values, and call the method of putStudent native, then we need to call in C ++, Java Student in and modify the value of the age and name of.
You can see in the output, we not only call methods Student is in C ++, the name and age also modify the property value.
javap -s acquisition method signature
For the following method signature we can generate by javap -s
Find the following directory
to open the command line
, type:javap -s com.hongx.jni.Student
Paste the code
package com.hongx.jni;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
String TAG = "Hongx";
static {
System.loadLibrary("native-lib");
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView tv = findViewById(R.id.sample_text);
tv.setText(stringFromJNI());
//test01();
// test02();
test03();
}
public native String stringFromJNI();
public native void test01();
public native void addTest01(int number, String text, int[] intArray, String[] array);
public native void putStudent(Student student);
public void test03() {
Student student = new Student();
student.age = 98;
student.name = "雄霸";
putStudent(student);
}
public void test02() {
int[] ints = {1,2,3,4,5,6};
String[] strings = {"李小龙", "李连杰"};
addTest01(9527, "李元霸", ints, strings);
for (int anInt : ints) {
Log.d(TAG, "test02: " + anInt);
}
}
}
package com.hongx.jni;
import android.util.Log;
public class Student {
private final static String TAG = Student.class.getSimpleName();
public String name;
public int age;
public String getName() {
return name;
}
public void setName(String name) {
Log.d(TAG, "Java setName: name:" + name);
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
Log.d(TAG, "Java setAge: age:" + age);
this.age = age;
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
public static void myStaticMethod() {
Log.d(TAG, "myStaticMethod: ");
}
}
#include <jni.h>
#include <string>
#include <android/log.h>
#define TAG "Hongx"
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, TAG, __VA_ARGS__)
extern "C" JNIEXPORT jstring JNICALL
Java_com_hongx_jni_MainActivity_stringFromJNI(
JNIEnv *env,
jobject /* this */) {
std::string hello = "Hello from C++";
return env->NewStringUTF(hello.c_str());
}
extern "C" // 支持C语言的代码
JNIEXPORT // Linux 和 Windows jni.h 内部定义全部都不一样，此宏代表我要暴露出去的标准形式定义
// 例如：在Windows中，对外暴露的标准就规定了，所以函数必须是Windows系统规则定义的
void JNICALL // Linux 和 Windows jni.h 内部定义全部都不一样，此宏代表 当前函数 压栈规则（行参规则）
// 例如：Windows中：代表函数压栈 从右 到 左边
Java_com_hongx_jni_MainActivity_test01(JNIEnv *env, jobject thiz) {
LOGD("test01");
}
extern "C"
JNIEXPORT void JNICALL
Java_com_hongx_jni_MainActivity_addTest01(JNIEnv *env, // Java虚拟机 自动携带过来的，就是为了 让我们可以使用JNI的API
jobject thiz, // java中的 MainActivity 这个实例
jint number,jstring text,jintArray int_array,jobjectArray string_array) {
// C领域中 JNI领域中 Java领域中
// int jint int
// const char * jstring String
int my_number = number;
LOGD("my_number: %d\n", my_number);
// 参数二：第一重意思：是否在内部完成Copy操作，NULL==0 false， 第二重意思：要给他一个值，让内部可以转起来，这个值，随意
const char *my_text = env->GetStringUTFChars(text, NULL);
LOGD("my_text: %s\n", my_text);
// 回收 GetStringUTFChars
env->ReleaseStringUTFChars(text, my_text);
// 打印Int数组
// jint* GetIntArrayElements(jintArray array, jboolean* isCopy)
jint *my_int_array = env->GetIntArrayElements(int_array, NULL);
// jsize GetArrayLength(jarray array)
jsize intsize = env->GetArrayLength(int_array);
for (int i = 0; i < intsize; ++i) {
int result = *(my_int_array + i);
*(my_int_array + i) += 1000;
LOGD("遍历IntArray里面的值：%d\n", result);
}
// 回收
env->ReleaseIntArrayElements(int_array, my_int_array, 0); // 0代表要刷新
// 打印String数组
jsize jsize1 = env->GetArrayLength(string_array);
for (int i = 0; i < jsize1; i++) {
jobject jobject1 = env->GetObjectArrayElement(string_array, i);
jstring jstring1 = static_cast<jstring>(jobject1);
const char *itemStr = env->GetStringUTFChars(jstring1, NULL);
LOGD("遍历String Array 里面的值：%s\n", itemStr);
env->ReleaseStringUTFChars(jstring1, itemStr); // 回收
}
}
extern "C"
JNIEXPORT void JNICALL
Java_com_hongx_jni_MainActivity_putStudent(JNIEnv *env,
jobject thiz,
jobject student) {
// C领域中 JNI领域中 Java领域中
// jclass class
// jmethodID Method
// 1.获取字节码
const char * student_clss_str = "com/hongx/jni/Student";
jclass student_class = env->FindClass(student_clss_str);
// 2.拿到方法对象
const char * sig = "(Ljava/lang/String;)V"; // 方法签名 javap -s 全类名 必须在.class下
jmethodID setName = env->GetMethodID(student_class, "setName", sig);
sig = "(I)V";
jmethodID setAge = env->GetMethodID(student_class, "setAge", sig);
sig = "()V";
jmethodID myStaticMethod = env->GetStaticMethodID(student_class, "myStaticMethod", sig);
// 3.调用对象
const char * str = "AAAAAAAA";
jstring str2 = env->NewStringUTF(str);
env->CallVoidMethod(student, setName, str2);
env->CallVoidMethod(student, setAge, 888);
env->CallStaticVoidMethod(student_class, myStaticMethod);
env->DeleteLocalRef(student_class); // 回收
env->DeleteLocalRef(student); // 回收
}
