int 对象到整数转换的问题

Question

对于我的一个项目，我正在使用 Java 本机接口 (JNI)。

我的项目包含一个 JNI 系统，它使用端口参数在 de C++ 端调用一个函数。此函数返回一个 Object 数组，如下面的 cmets 中所写，问题在最后一条评论中说明：

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];
}

有没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

铸造不会改变对象的类型。为了将 result[1] 转换为 Integer，result[1] 必须已经是整数。

你没有说数组中有什么类型的对象。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东西，因为任何对象都可以是对象的子类。

你说数组中的值有值，但你没有说你是怎么知道的或者你有什么样的值。您给出的错误消息与您的解释并不完全相符。所以很难说到底发生了什么。但是您没有要转换的 Integer 对象，这就是转换不起作用的原因。

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[]。