nonemptybookmarks.java

书籍"Java_面向事件编程"的附带光盘代码

// a recursive data structure that stores a list of bookmarks
class NonemptyBookmarks extends EmptyBookmarks {
    
    private EmptyBookmarks rest;
    private Bookmark first;
    private int mysize;

    public NonemptyBookmarks(EmptyBookmarks list, Bookmark entry)
    {
        rest = list;
        first = entry;
        mysize = rest.getSize() + 1;
    }

    // if this bookmark is at the desired position, return it,
    // otherwise decrement the desired position and pass the call
    // on to the rest of the list
    public Bookmark getSelectedItem( int position ) {
        if ( position == 0 )
            return first;
        else try {
            return rest.getSelectedItem( position-1);
        }catch (IllegalArgumentException e) {
            throw new IllegalArgumentException("Index "+position+" is out of range");
        }
    }
    
    public int getSize() {
        return mysize;
    }
    
    
    public boolean isemtpy()
    {
        return false;
    }
        
}