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<qhelp>

<overview>

<p>A type wildcard with an <code>extends</code> clause (for example

<code>?&nbsp;extends&nbsp;String</code>) implicitly suggests that a type (in

this case <code>String</code>) has subclasses. If the type in the <code>extends</code>

clause is final, the code is confusing because a final class cannot have

any subclasses. The only type that satisfies <code>?&nbsp;extends&nbsp;String</code> is

<code>String</code>.</p>

</overview>

<recommendation>

<p>To make the code more readable, omit the wildcard to leave just the final type.</p>

</recommendation>

<example>

<p>In the following example, a wildcard is used to refer to any type that is a subclass of

<code>String</code>.</p>

<sample src="TypeVarExtendsFinalType.java" />

<p>However, because <code>String</code> is declared <code>final</code>, it does not have any

subclasses. Therefore, it is clearer to replace <code>?&nbsp;extends&nbsp;String</code> with

<code>String</code>.</p>

</example>

<references>

<li>

Help - Eclipse Platform:

<a href="https://help.eclipse.org/2020-12/advanced/content.jsp?topic=/org.eclipse.jdt.doc.user/reference/preferences/java/compiler/ref-preferences-errors-warnings.htm">Java Compiler Errors/Warnings Preferences</a>.

</li>

<li>

Java Language Specification:

<a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-4.html#jls-4.5.1">4.5.1 Type Arguments of Parameterized Types </a>,

<a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-8.html#jls-8.1.1.2">8.1.1.2 final Classes</a>.

</li>

</references>

</qhelp>