CodeQL documentation

Type variable hides another type

ID: java/type-variable-hides-type
Kind: problem
Severity: warning
Precision: medium
   - reliability
   - readability
   - types
Query suites:
   - java-security-and-quality.qls

Click to see the query in the CodeQL repository

Type shadowing occurs if two types have the same name but one is defined within the scope of the other. This can arise if you introduce a type variable with the same name as an imported class.

Type shadowing may cause the two types to be confused, which can lead to various problems.


Name the type variable so that its name does not clash with the imported class.


In the following example, the type java.util.Map.Entry is imported at the top of the file, but the class Mapping is defined with two type variables, Key and Entry. Uses of Entry within the Mapping class refer to the type variable, and not the imported interface. The type variable therefore shadows Map.Entry.

import java.util.Map;
import java.util.Map.Entry;

class Mapping<Key, Entry>  // The type variable 'Entry' shadows the imported interface 'Entry'.
	// ...

To fix the code, the type variable Entry on line 4 should be renamed.