Java 参数类型错误

Question

IDE 提示:“第二个参数类型错误:找到 boolean 值，必需:？”

public void onItemClick(View view, int positon) {
    HashMap<String, ?> movie = (HashMap<String, ?>) movieData.getItem(positon);

    if(view.getId() == R.id.checkBox) {
        boolean selection = (boolean) movie.get("selection") ? false : true;

        // Error here
        movie.put("selection", selection);
    }
}

但是，这个可以工作

public void onItemClick(View view, int positon) {
    HashMap movie = movieData.getItem(positon);

    if(view.getId() == R.id.checkBox) {
        boolean selection = (boolean) movie.get("selection") ? false : true;

        movie.put("selection", selection);
    }
}

Answer 1

在 Unbounded Wildcards 的 Java 教程页面中，它指出:

It's important to note that List<Object> and List<?> are not the same. You can insert an Object, or any subtype of Object, into a List<Object>. But you can only insert null into a List<?>. The Guidelines for Wildcard Use section has more information on how to determine what kind of wildcard, if any, should be used in a given situation.

您应该考虑此处使用通配符的原因。如果可能，不要使用通配符。如果您仍需要使用一个，请使用适当的 Upper Bounded Wildcard这样就可以知道类型。

由于您正在存储 Boolean在其他数据类型中，唯一的共同父级是 Object :

HashMap<String, Object> movie;