<div dir="ltr">This question would probably be better asked on Stack Overflow or the like. The short answer is that the compiler is following the language spec. <a href="https://docs.oracle.com/javase/specs/jls/se24/html/jls-4.html#jls-4.8">§4.8</a> says:<br><p class="gmail-norm-static" style="color:rgb(0,0,0);font-size:12px">> The type of a constructor (<a class="gmail-xref" href="https://docs.oracle.com/javase/specs/jls/se24/html/jls-8.html#jls-8.8" title="8.8. Constructor Declarations">§8.8</a>), instance method (<a class="gmail-xref" href="https://docs.oracle.com/javase/specs/jls/se24/html/jls-8.html#jls-8.4" title="8.4. Method Declarations">§8.4</a>, <a class="gmail-xref" href="https://docs.oracle.com/javase/specs/jls/se24/html/jls-9.html#jls-9.4" title="9.4. Method Declarations">§9.4</a>), or non-<code class="gmail-literal">static</code> field (<a class="gmail-xref" href="https://docs.oracle.com/javase/specs/jls/se24/html/jls-8.html#jls-8.3" title="8.3. Field Declarations">§8.3</a>) of a raw type <span class="gmail-type">C</span> that is not inherited from its superclasses or superinterfaces is the erasure of its type in the generic class or interface <span class="gmail-type">C</span>.</p>It <i>doesn't</i> say that this only applies when the original type references the type parameters that have been omitted from the raw type. So the return type of getValues() in the raw Child is raw List, even though the original type List<String> doesn't mention T.</div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Tue, 10 Jun 2025 at 08:50, Jean-Noël Rouvignac <<a href="mailto:jean-noel.rouvignac@pingidentity.com">jean-noel.rouvignac@pingidentity.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>Hello,</div><div><br></div><div>When doing refactorings to take advantage of newer Java features, I hit a new and weird edge case. I trimmed down the code several times, and ended up with the following tiny reproducer, and I don't understand what javac is complaining about even with javac 24:<br><div><div><br></div><div>(Note: unlike the original code, this reproducer is very contrived,
so there's no need to make comments on how bad it is: I fully agree)</div></div><br>```java<br>1 import java.util.ArrayList;<br>import java.util.List;<br>import java.util.stream.Collectors;<br><br>public class Main {<br> private static final class Child<T> {<br> public List<String> getValues() {<br> return new ArrayList<>();<br> }<br> }<br><br> @SuppressWarnings("unchecked")<br> private static String getString1(Child c) {<br> // Compilation error:<br> // Main.java:16: error: incompatible types: Object cannot be converted to String<br> return c.getValues().stream().collect(Collectors.joining());<br> }<br><br> private static String getString2(Child c) {<br> // Compilation error:<br> // Main.java:27: warning: [unchecked] unchecked conversion<br> // List<String> values = c.getValues();<br> // ^<br> // required: List<String><br> // found: List<br> //1 warning<br> List<String> values = c.getValues();<br> return values.stream().collect(Collectors.joining());<br> }<br>}<br>```<br><br>It turns out IntelliJ is a bit more eloquent than javac, and when hovering over the warning on `c.getValues()` at the line with `List<String> values = c.getValues();`, it reports the following:<br><br>> Unchecked assignment: 'java.util.List' to
'java.util.List<java.lang.String>'. Reason: 'c' has raw type, so
result of getValues is erased <br><br></div><div>Is it possible that javac is doing early type erasure when analysing this code, erasing a bit too much? Even if the code uses `Child` without type argument, I would expect the return type of `getValues()` to be well defined as `List<String>`?<br><br></div><div>What do you think?<br></div><div>I am sure there is some rational explanation that I missed for this behaviour. I could not find a JBS issue showing the same case as here.</div><div><br></div><div>Thank you,</div><div>Jean-Noël Rouvignac</div></div>
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