静态类非静态成员

Question

I'm reading a book on android game development and I've come across the first patch of code:

public static class KeyEvent {
    public static final int KEY_DOWN = 0;
    public static final int KEY_UP = 1;

    public int type;
    public int keyCode;
    public char keyChar;
}

It is my understanding that anything static means there can only be one instance of it.

If there can only ever be one instance of KeyEvent why are type , keyCode and keyChar not declared static as well?

Answer 1

Only nested classes can be declared as static ; not outer/normal classes. It allows you to use the static inner class without instantiating the outer class.

Answer 2

Your code is an nested class . static modifier means here that this class is accessible without creating outer class object.

Assuming that outer class is called OuterClass you can call:

KeyEvent ke = new OuterClass.KeyEvent();

Answer 3

static does not really mean "there can only be one instance of it".

If you are using the static keyword in any declaration within a class, static means "what I declare here is not a member of an instance of the enclosing class, but it is a member of the class itself ."

That being said, if you're declaring a nested class (a class within a class) as static, then it means that the nested class declaration does not rely on an instance of the enclosing class, and can be instantiated directly.