Question about method calling (Java 1.5.0_05)

Question

Imagine for example the javax.swing.border.Border hierarchy.
I'm writing a BorderEditor for some gui builder, so I need a function that takes a Border instance and returns the Java code. Here is my first try:
1 protected String getJavaInitializationString() {
2     Border border = (Border)getValue();
3     if (border == null)
4         return "null";
5
6     return getCode(border);
7 }
8
9 private String getCode(BevelBorder border) {...}
10 private String getCode(EmptyBorder border) {...}
11 private String getCode(EtchedBorder border) {...}
12 private String getCode(LineBorder border) {...}
13
14 private String getCode(Border border) {
15     throw new IllegalArgumentException("Unknown border class " + border.getClass());
16 }This piece of code fails. Because no matter of what class is border in line 6, this call always ends in String getCode(Border border).
So I replaced line 6 with:
6     return getCode(border.getClass().cast(border));But with the same result. So, I try with the asSubClass() method:
6     return getCode(Border.class.asSubClass(border.getClass()).cast(border));And the same result again! Then i try putting a concrete instance of some border, say BevelBorder:
6     return getCode(BevelBorder.class.cast(border));Guess what! It worked! But this is like:
6     return getCode((BevelBorder)border);And I don't want that! I want dynamic cast and correct method calling.
After all tests, I give up and put the old trusty and nasty if..else if... else chain.
Too bad! I'm doing some thing wrong?
Thank in advance
Quique.-
PS: Sorry about my english! it's not very good! Escribo mejor en espa�ol!

Answer 1

Hi, your spanish is quite good!
getCode(...) returns the Java code for the given border.
So getCode(BevelBorder border) returns a Java string that is something like this "new BevelBorder()".
I want Java to resolve the method to call.
For example: A1, A2 and A3, extends A.
public void m(A1 a) {...}
public void m(A2 a) {...}
public void m(A3 a) {...}
public void m(A a) {...}
public void p() {
    A a = (A)getValue();
    // At this point 'a' could be instance of A1, A2 or A3.
    m(a); // I want this method call, to call the right method.
}This did not work. So, i've used instead of m(a):
    m(a.getClass().cast(a));Didn't work either. Then:
    m(A.class.asSubClass(a.getClass()).cast(a));No luck! But:
    m(A1.class.cast(a)); // idem m((A1)a);Woks for A1!
I don't know why m(A1.class.cast(a)) works and m(a.getClass().cast(a)) doesn't!
thanks for replying!
Quique