Doubt in overloading

[aleyx chow]

  
class animal{}
class cat extends animal{}
 
class methods{
void invoke(animal a,animal b){}  //method 1
void invoke(animal a,cat b){}    //method 2
void invoke(cat a,animal b){}    //method 3
void invoke(cat a,cat b){}       //method 4
}
 
public class Test{
methods method=new methods();
//insert code here Line 5
}

which method would be invoke if the code at line 5 is
method.invoke(null,null);
if i disable the method 4, method.invoke(null,null)would invoke which method or occur a compile err?

i found a way to get the answer but im not sure it will always do the right things. For example,
first list out the inhirency chain and mark them a value like following:

animal 2
|___cat 1
null 0

second caculate them with the methods param list.
result
method.invoke(null,null); / 0 / 0
1.void invoke(animal a,animal b){} / 2 / 2 / (2-0)+(2-0)
2.void invoke(animal a,cat b){} / 2 / 1 / 3
3.void invoke(cat a,animal b){} / 1 / 2 / 3
4.void invoke(cat a,cat b){} / 1 / 1 / 2

the No.4 result is min, so the code method.invoke(null,null)will invoke the method invoke(cat, cat)
if i disable the method 4,then there will be two same result 3 and 3,so it occur compile err becauseof ambigious method param list.

Is it a right way? and some one can show me the rules for invoking a method by the param list?thanx.
[ June 07, 2005: Message edited by: aleyx chow ]

[Nik Raut]

I guess your approach is right but someone should give a more specific explanation. Anyone???

[ankur rathi]

The method which is more specific, always get called but if compiler feel problem in deciding specific one then gives 'ambigous method' error.

Hope it helps.

[amit taneja]

class animal{}
class cat extends animal{}
class methods{
void invoke(animal a,animal b){System.out.println(" A A");} //method 1
void invoke(animal a,cat b){System.out.println(" A C");} //method 2
void invoke(cat a,animal b){System.out.println(" C A");} //method 3
void invoke(cat a,cat b){System.out.println(" C C");} //method 4
}
public class Test14{
methods method=new methods();
//insert code here Line 5
method.invoke (new animal, new animal);
}

why this error is comming...??


D:\java_prac>javac Test14.java
Test14.java:12: <identifier> expected
method.invoke (new animal, new animal);
^
1 error

[Tony Thompson]

Amit,
I could be missing a larger issue here but you should have parentheses on your 'animal' constructors as in: method.invoke(new animal(), new Animal());

HTH,
Tony

[Nikhil Pancholi]

Originally posted by amit taneja:

public class Test14{
methods method=new methods();
//insert code here Line 5
method.invoke (new animal, new animal);
}

why this error is comming...??

1 error

How can one invoke a method from a class?

Shouldn't it be something like

public class Test14{
methods method = new methods();
public static void main(String[] args)
{
Test14 test = new Test14();
test.method.invoke(new animal(), new animal());
}
}

?

[amit taneja]

Originally posted by Nikhil Pancholi:

Originally posted by amit taneja:
[qb]
public class Test14{
methods method=new methods();
//insert code here Line 5
method.invoke (new animal, new animal);
}

why this error is comming...??

1 error

How can one invoke a method from a class?

Shouldn't it be something like

public class Test14{
methods method = new methods();
public static void main(String[] args)
{
Test14 test = new Test14();
test.method.invoke(new animal(), new animal());
}
}

?[/QB]

ya ur right..i don't know how i ignore such silly thing..

[vjy chin]

I couldnt understand the reasoning, I apologize.
It would be great if anyone can explain in layman terms.

Thanks

[Vishnu Prakash]

How can one invoke a method from a class?

Shouldn't it be something like

public class Test14{
methods method = new methods();
public static void main(String[] args)
{
Test14 test = new Test14();
test.method.invoke(new animal(), new animal());
}
}

This is wrong. This will produce a compile time error. Since we are not dealing with any inner classes we don't need a instance of Test14.

method.invoke (new animal(), new animal());
The above method call is correct and will produce output as :
A A