Question

对于我的项目，我正在使用Java Native Interface（JNI）。

我的项目包含一个JNI系统，该系统使用port参数调用de C ++端的函数。这个函数比返回一个Object数组，如下面的注释中所写，问题在最后的评论中说明：

public Integer SpawnNewConnectionHandler(Integer Port) throws WrapperException {
    //Creation of the object array that will hold the result
    Object[] result;

    //Get the result object array from the external library. Length of the array is either 1 or 2.
    //While debugging i found out that it contains two elements of the type int (Not integer, but its basetype).
    //This means that nothing on the c++ side went wrong.
    result = spawnNewServerConnectionHandler(Port);

    //Error coming from the SDK should be handled here. (Code snipped as the if clause checking for it, is not being called.)
    //The snipped will throw a WrapperException if the length of the array returned is not 1.

    //The debugger will break here and show me that before executing this line both of the result objects are not empty,
    //So result[0] and result[1] are filled with data, for result[1] it is a 1 or higher. For result[0] is is the number 0. (Returned as a fact that everything went alright while executing.)
    //During execution of this line the program crashes and shows a NullPointerException.
    //
    //I found out that it is impossible for it to cast the object, stored in the object array as a int into a Integer.
    //Doing this manually while debugging shows the following error message:
    //"Unable to cast numeric value to java.lang.Integer."
    return (Integer) result[1];
}

有人知道这个问题的解决方案，或者至少为什么它会给我这个奇怪的错误？

Answer 1

转换不会更改对象的类型。为了将结果[1]强制转换为整数，结果[1]必须已经是一个整数。

您没有说明数组中的对象类型。我知道数组被声明为Object，但这意味着数组中的对象可以是任何对象，因为任何对象都可以是对象的子类。

您说数组中的值具有值，但您没有说明您是如何知道这些值或您拥有的值。您排序的错误消息与您的解释并不完全匹配。所以很难确切地说出发生了什么。但是你没有要转换的Integer对象，这就是演员无效的原因。

Answer 2

根据您对@rcook的评论，您似乎有一个int[]数组，而不是Integer[]。这里的区别在于int是primitive type而Integer是对象类型。

试试这个：

public Integer SpawnNewConnectionHandler(Integer Port) throws WrapperException {
    //Creation of the object array that will hold the result
    int[] result;

    //Get the result object array from the external library. Length of the array is either 1 or 2.
    //While debugging i found out that it contains two elements of the type int (Not integer, but its basetype).
    //This means that nothing on the c++ side went wrong.
    result = (int[]) spawnNewServerConnectionHandler(Port);

    //Error coming from the SDK should be handled here. (Code snipped as the if clause checking for it, is not being called.)
    //The snipped will throw a WrapperException if the length of the array returned is not 1.

    //The debugger will break here and show me that before executing this line both of the result objects are not empty,
    //So result[0] and result[1] are filled with data, for result[1] it is a 1 or higher. For result[0] is is the number 0. (Returned as a fact that everything went alright while executing.)
    //During execution of this line the program crashes and shows a NullPointerException.
    //
    //I found out that it is impossible for it to cast the object, stored in the object array as a int into a Integer.
    //Doing this manually while debugging shows the following error message:
    //"Unable to cast numeric value to java.lang.Integer."
    return Integer.valueOf(result[1]);
}

请注意，我已将所有对Object[]的引用替换为int[]。

int对象到整数转换的问题

2 个答案: