Parent Class References Child Class

ID

java.parent_class_references_child

Severity

high

Remediation Complexity

medium

Remediation Risk

low

Remediation Effort

medium

Resource

Code Smell

Language

Java

Tags

code-style, reliability

Description

Reports references from a parent class to one of its subclasses within the same compilation unit. This constitutes an inverted dependency that tightly couples the parent to its children.

Rationale

A well-designed type hierarchy has children depending on parents, never the reverse. When a parent class directly references a subclass — via new ChildClass(), instanceof ChildClass, a field of type ChildClass, or any other reference — the dependency is inverted. This creates:

  • Cyclic coupling — parent and child cannot be compiled, tested, or evolved independently.

  • Fragile base class — adding, renaming, or removing a subclass forces changes in the parent.

  • Violated Open/Closed Principle — extending the hierarchy requires modifying the existing parent class.

// Bad -- parent knows about child
class Shape {
    boolean isCircle() {
        return this instanceof Circle;
    }
}
class Circle extends Shape {}

Remediation

Move child-specific logic into the child class using polymorphism, or use a factory / registry pattern external to the hierarchy.

// Good -- polymorphism instead of instanceof
abstract class Shape {
    abstract String kind();
}
class Circle extends Shape {
    @Override String kind() { return "circle"; }
}

References