为什么用Java返回false？

Question

I'm writing an Android app that uses an AdapterView. There are multiple calls to IsInFilterMode() in the AdapterView class which simply is a one line function that returns false. I can't override the function so I can't for the life of me figure out why this function exists if it just returns false. The description says that it returns true if it's in filter mode. Here is the definition of IsInFilterMode() :

 /**
 * Indicates whether this view is in filter mode. Filter mode can for instance
 * be enabled by a user when typing on the keyboard.
 *
 * @return True if the view is in filter mode, false otherwise.
 */
boolean isInFilterMode() {
    return false;
}

I am relatively new to Java so perhaps I'm missing something that is typical to Java source code here? Is there other code that is be obfuscated from me?

Answer 1

First, the lack of a visibility modifier is often referred to as package-private . It is in between protected and private on the visibility scale- only other classes within the same package can override package-private methods. See Controlling Access to members of a Class for more information.

The Android framework uses this often- it allows the framework to override those methods without allowing the end users (Android developers) to do the same and potentially interfere with how the framework operates.

In this case, the default for AdapterView s is to not support filter mode at all.

Some AdapterView subclasses do support it. For example, AbsListView and it's descendants do. In the case of AbsListView , this method returns the value of an internal property that tracks whether or not the list is actually in filter mode.