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Doubt on Varargs and overriding

 
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Hi,

I am reading the SCJP Tiger Study Guide, I don't quite follow how the overriding with varargs works on the example given. Please help me out.

public class OneSuperclass {
public int doIt(String str, Integer... data) throws java.io.EOFException,
java.io.FileNotFoundException { // (1)
String signature = "(String, Integer[])";
out.println(str + " => " + signature);
return 1;
}

public void doIt(String str, Number... data) { // (2)
String signature = "(String, Number[])";
out.println(str + " => " + signature);
}
}

import static java.lang.System.out;

public class OneSubclass extends OneSuperclass {

public int doIt(String str, Integer[] data) // Overridden (a)
//public int doIt(String str, Integer... data) // Overridden (b)

throws java.io.FileNotFoundException {
String signature = "(String, Integer[])";
out.println("Overridden: " + str + " => " + signature);
return 0;
}

public void doIt(String str, Object... data) { // Overloading
String signature = "(String, Object[])";
out.println(str + " => " + signature);
}

public static void main(String[] args) throws Exception {
OneSubclass ref = new OneSubclass();
ref.doIt("1. (String)");
ref.doIt("2. (String, int)", 10);
ref.doIt("3. (String, Integer)", new Integer(10));
ref.doIt("4. (String, int, byte)", 10, (byte) 20);
ref.doIt("5. (String, int, int)", 10, 20);
ref.doIt("6. (String, int, long)", 10, 20L);
ref.doIt("7. (String, int, int, int)", 10, 20, 30);
ref.doIt("8. (String, int, double)", 10, 20.0);
ref.doIt("9. (String, int, String)", 10, "what?");
ref.doIt("10.(String, boolean)", false);
}
}

It says that with overriden(a), the output will be the following:
1. (String) => (String, Number[])
2. (String, int) => (String, Number[])
3. (String, Integer) => (String, Number[])
4. (String, int, byte) => (String, Number[])
5. (String, int, int) => (String, Number[])
6. (String, int, long) => (String, Number[])
7. (String, int, int, int) => (String, Number[])
8. (String, int, double) => (String, Number[])
9. (String, int, String) => (String, Object[])
10.(String, boolean) => (String, Object[])

But with overriden (b), the output is:
Overridden: 1. (String) => (String, Integer[])
Overridden: 2. (String, int) => (String, Integer[])
Overridden: 3. (String, Integer) => (String, Integer[])
4. (String, int, byte) => (String, Number[])
Overridden: 5. (String, int, int) => (String, Integer[])
6. (String, int, long) => (String, Number[])
Overridden: 7. (String, int, int, int) => (String, Integer[])
8. (String, int, double) => (String, Number[])
9. (String, int, String) => (String, Object[])
10.(String, boolean) => (String, Object[])

My doubt is:
For output statment 1, 2, 3, 5, 7, When overriden (a) is used, why the OneSuperclass.doIt(String str, Number... data) operation is chosen? Why not OneSubclass.doIt(String str, Integer... data)? Isn't the signature of OneSubclass.doIt(String str, Integer... data) is more matching with the input parameter?

Thanks!


Lyn
[ October 02, 2005: Message edited by: Lyn Yang ]
 
Lyn Yang
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no answer?

Somebody please help...
 
Ranch Hand
Posts: 220
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Originally posted by Lyn Yang:
Hi,

But with overriden (b), the output is:


My doubt is:
For output statment 1, 2, 3, 5, 7, When overriden (a) is used, why the OneSuperclass.doIt(String str, Number... data) operation is chosen? Why not OneSuperclass.doIt(String str, Integer... data)? Isn't the signature of OneSuperclass.doIt(String str, Integer... data) is more matching with the input parameter?

Thanks!


Lyn



Overridden: 1. (String) => (String, Integer[])
Overridden: 2. (String, int) => (String, Integer[])
Overridden: 3. (String, Integer) => (String, Integer[])
4. (String, int, byte) => (String, Number[])
Overridden: 5. (String, int, int) => (String, Integer[])
6. (String, int, long) => (String, Number[])
Overridden: 7. (String, int, int, int) => (String, Integer[])
8. (String, int, double) => (String, Number[])
9. (String, int, String) => (String, Object[])
10.(String, boolean) => (String, Object[])


See, the compiler runs this way
1. sees if there's a method that matches the sign exactly without any modification
2. it sees if something can be matched after boxing/unboxing all without varargs
3. it sees if something can be matched after boxing/unboxing and varargs

when you box a long, you get a Long which is a subclass of Number and not of Integer, the same is the case with short > Short extends Number

thats why, hope its clear now.
 
Lyn Yang
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Thanks, Akshay Kiran. However, what I don't understand is when the overriden (a) operation is used in the subclass i.e.
public int doIt(String str, Integer[] data)

However, I think I know the answer when I tried to reorganize the question. I got myself confused as I messed up the overidden (a) and overriden(b)

When the overriden (a) is used, the OneSubclass.doIt(String str, Integer[] data) is not a vararg, so it is expecting an array. Therefore, the 1, 2, 3, 5, 7 will call the OneSuperclass.doIt(String str, Number... data).

B.T.W. Your summary of how compiler works is very clear and precise. Thank you.
 
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