CodeQL documentation

Equals on incomparable types

ID: java/equals-on-unrelated-types
Kind: problem
Security severity: 
Severity: error
Precision: very-high
   - reliability
   - correctness
Query suites:
   - java-security-and-quality.qls

Click to see the query in the CodeQL repository

Calls of the form x.equals(y), where x and y have incomparable types, should always return false because the runtime types of x and y will be different. Two types are incomparable if they are distinct and do not have a common subtype.


Ensure that such comparisons use comparable types.


In the following example, the call to equals on line 5 refers to the whole array by mistake, instead of a specific element. Therefore, “Value not found” is returned.

String[] anArray = new String[]{"a","b","c"}
String valueToFind = "b";

for(int i=0; i<anArray.length; i++){
  if(anArray.equals(valueToFind){    // anArray[i].equals(valueToFind) was intended
    return "Found value at index " + i;

return "Value not found";


  • © GitHub, Inc.
  • Terms
  • Privacy