Name clash - Type erasure

[Faber Siagian]

Dear all,
The following program was taken from K&B Bonus Master Exam, but i have made a lot of modification.

<blockquote>code:

---

<pre name="code" class="core">class Base
{
public List<?> asList(List<?> x) { return null; } //line 1
}
class Derived extends Base
{
public List<String> asList(List<String> x) { return null;} // line 2
}</pre>

---

</blockquote>

Compilation error :

name clash: asList(java.util.List<java.lang.String> in Derived and asList(java.util.List<?> in Base have the same erasure, yet neither overrides the other

In this case, does Derived's asList() override Base's asList() ?
How is actually "type erasure" applied in the code ? What part of it raised the error ?

[Chandra Bhatt]

<blockquote>code:

---

<pre name="code" class="core"> class Base{
public List<?> asList(List<?> x)
{ return null; } //line 1}

class Derived extends Base{
public List<String> asList(List<String> x) {
return null;} // line 2
}
</pre>

---

</blockquote>

After type erasure, both the methods will be having same signature, hence no override, therefore compilation error.
[ July 15, 2008: Message edited by: Chandra Bhatt ]

[Raphael Rabadan]

Originally posted by Chandra Bhatt:
<blockquote><font size="1" face="Verdana, Arial">code:</font><hr><pre name="code" class="core"><font size="2"> class Base{
public List<?> asList(List<?> x)
{ return null; } //line 1}

class Derived extends Base{
public List<String> asList(List<String> x) {
return null;} // line 2
}
</font></pre><hr></blockquote>

After type erasure, both the methods will be having same signature, hence no override, therefore compilation error.

[ July 15, 2008: Message edited by: Chandra Bhatt ]

What's the problem here? I couldn't get it..

[Ralph Jaus]

both the methods will be having same signature, hence no override

I thought having the same signature is a precondition for overriding ?? Am I totally wrong ?

When I was studying for SCJP 1.5, I took some mock exams from www.javablackbelt.com and had been confronted with similar questions. But in my experience, type erasure is beyond the scope of SCJP.

I wouldn't be sure if it really helps for SCJP going into depth there. But what do the others mean ?

[Milan Sutaria]

i agree with Ralph on the "same signature being a pre-requisite for overriding methods"
can some1 explain the reason for compilation error?

[Faber Siagian]

If i change the code :

<blockquote>code:

---

<pre name="code" class="core">class Base
{
public List asList(List x)
{
return null;
} //line 1
}

class Derived extends Base
{
public List asList(List x)
{
return null;
} // line 2
}</pre>

---

</blockquote>

There should be no problem if the code is compiled.
I think, code above is the result of type erasure, because all of the type are removed. But then why i get compiler error if i use the code with the type argument ?