I find myself writing a lot of {@link ...} tags
into Javadoc. It can be annoying to have to type
out (and remember) the full class and member name,
when code completion works fine in normal code.
Perhaps within Javadoc comments this tag - which
refers to other classes or members - could get
completion from the regular parser database. E.g.

package a;
public class A {
    public int x;
    public void foo() {}
}
package b;
import a.*;
public class B {
    public int y;
    protected void bar(int i) {}
    protected void bar(boolean b) {}
    /** Comment.. <<CARET>> */
    public void whatever() {}
}

At the marked point, typing

    {@link <<CARET>>

could offer completions:

    #whatever
    #bar(int)
    #bar(boolean)
    #y
    B
    A
    A#x
    A#foo
    java.util.Collections#singleton

etc. Basically the same things that regular code
completion would offer you, but with a somewhat
different syntax.

@see could work the same way, assuming you did not
begin the body with '"' or '<' which begin a
different syntax.