misunderstanding about generic
see those codes
public class C1{
// do something
}
public class C2 extends C1{
// do something
}
public class TestClass{
public void FuncA(ArrayList<C1>){
// do something
}
public static void main(String args[]){
TestClass clazz = new TestClass();
ArrayList<C2> aList = new ArrayList<C2>();
// do something
clazz.FuncA(aList); // < attention please!
}
}
It's just a simple use of Generic feature.I define a Function with a parameter in type ArrayList, and I also take the generic feature into the lines.
But just at compile time, IDE tells me that:
The method FuncA(ArrayList<C1>) in the type TestClass is not applicable for the arguments (ArrayList<C2>)
I know the Java language may treate this feature strictly, but in my way, it also performs a safely use!Because C2 is derived from C1,I use a sub-type as parameter to pass into function which is defined with a parameter in parent-type, it's very safy...
How should I consider this...
[1134 byte] By [
Eliottea] at [2007-11-27 7:58:39]
It's not safe, cause what you're saying in your code is the following:
1.) aList is a list that's guaranteed to contain instances of C2
2.) FuncA is a method that works with lists which are guaranteed to contain instances of C1
So far, so good. Unfortunately, FuncA might add a C1 to its list parameter; this way it would break 1.)
So,as you said,generic must be very strict, and no inheriting supported?
i.e.
FuncA(ArrayList<C1> aList){
for(C1 clazz : aList){
// do something
}
}
When I use objects contained in aList in method FuncA,I don't know that the object clazz either refer to type C1 or type C2.So I could only use it as an instance of type C1.
May be I misunderstand...
Anyway,thanks all of u.
T_T ... my poor English. I come from a non-English speaking country.
This works!!.
import java.util.*;
class C2{
//do something
}
public class C1 extends C2{
//do something
}
class TestClass{
public void FuncA(ArrayList<C1> list){
//do something
}
public static void main(String args[]){
TestClass clazz = new TestClass();
ArrayList<C1> aList = new ArrayList<C1>();
//do something
clazz.FuncA(aList); // < attention please!
}
}
> So,as you said,generic must be very strict, and no
> inheriting supported?
Oh yes, there is. Change the signature of FuncA to this:
public void FuncA(List<? extends C1> aList)
