我有一个 Object
有一个 HashMap
字段.当 Object
传递给 C 时,如何访问该字段?
I have an Object
that has a HashMap
field. When the Object
is passed to C, how can I access the field?
Object
的Class
有以下字段:
private String hello;
private Map<String, String> params = new HashMap<String, String>();
你的问题的答案真的归结为为什么你想将 Map
传递给C 而不是在 Java 中迭代您的 Map
并将内容传递给 C.但是,我该质疑为什么?
The answer to your question really boils down to why you'd want to pass a Map
to C rather than iterate your Map
in Java and pass the contents to C. But, who am I to question why?
您问如何访问 HashMap
(在您提供的代码中,Map
)字段?在 Java 中为其编写访问器方法,并在传递容器 Object
时从 C 中调用该访问器方法.下面是一些简单的示例代码,展示了如何将 Map
从 Java 传递到 C,以及如何访问 Map的
size()
方法代码>.从中,您应该能够推断出如何调用其他方法.
You ask how to access the HashMap
(in your provided code, Map
) field? Write an accessor method for it in Java and call that accessor method from C when you pass the container Object
. Below is some bare-bones sample code showing how to pass a Map
from Java to C, and how to access the size()
method of the Map
. From it, you should be able to extrapolate how to call other methods.
容器对象:
public class Container {
private String hello;
private Map<String, String> parameterMap = new HashMap<String, String>();
public Map<String, String> getParameterMap() {
return parameterMap;
}
}
将容器传递给 JNI 的主类:
Master Class which passes a Container to JNI:
public class MyClazz {
public doProcess() {
Container container = new Container();
container.getParameterMap().put("foo","bar");
manipulateMap(container);
}
public native void manipulateMap(Container container);
}
相关C函数:
JNIEXPORT jint JNICALL Java_MyClazz_manipulateMap(JNIEnv *env, jobject selfReference, jobject jContainer) {
// initialize the Container class
jclass c_Container = (*env)->GetObjectClass(env, jContainer);
// initialize the Get Parameter Map method of the Container class
jmethodID m_GetParameterMap = (*env)->GetMethodID(env, c_Container, "getParameterMap", "()Ljava/util/Map;");
// call said method to store the parameter map in jParameterMap
jobject jParameterMap = (*env)->CallObjectMethod(env, jContainer, m_GetParameterMap);
// initialize the Map interface
jclass c_Map = env->FindClass("java/util/Map");
// initialize the Get Size method of Map
jmethodID m_GetSize = (*env)->GetMethodID(env, c_Map, "size", "()I");
// Get the Size and store it in jSize; the value of jSize should be 1
int jSize = (*env)->CallIntMethod(env, jParameterMap, m_GetSize);
// define other methods you need here.
}
值得注意的是,我并不热衷于在方法本身中初始化 methodID 和类;this SO Answer 向您展示了如何缓存它们以供重复使用.
Of note, I'm not crazy about initializing methodIDs and classes in the method itself; this SO Answer shows you how to cache them for re-use.
这篇关于如何通过 JNI 将 HashMap 从 Java 发送到 C的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持html5模板网!