'instanceof' with incompatible type

Reports instanceof expressions where the expression that is checked has a class/interface type that neither extends/implements the class/interface type on the right-side of the instanceof expression, nor has subclasses that do.

Although it could be intended for e.g. library code, such a construct is likely erroneous, because no instance of any class declared in the project could pass this instanceof test.

Example:

  class Foo { }

  interface Bar { }
  
  class Main {
      void test(Foo f, Bar b) {
          if (f instanceof Bar) { // problem
              System.out.println("fail");
          }
          if (b instanceof Foo) { // problem
              System.out.println("fail");
          }
      }
  }

Locating this inspection

By ID

Can be used to locate inspection in e.g. Qodana configuration files, where you can quickly enable or disable it, or adjust its settings.

InstanceofIncompatibleInterface

Via Settings dialog

Path to the inspection settings via IntelliJ Platform IDE Settings dialog, when you need to adjust inspection settings directly from your IDE.

Settings or Preferences | Editor | Inspections | Java | Probable bugs

Inspection ID: InstanceofIncompatibleInterface

Suppressing Inspection

You can suppress this inspection by placing the following comment marker before the code fragment where you no longer want messages from this inspection to appear:

//noinspection InstanceofIncompatibleInterface

More detailed instructions as well as other ways and options that you have can be found in the product documentation:

IntelliJ IDEA 2025.3

Inspection Details
By default bundled with:	IntelliJ IDEA 2025.3, Qodana for JVM 2025.3,

Last modified: 03 December 2025