Sometimes functionality needs to be layered across multiple levels of abstraction. A Vehicle defines basic movement, a Car adds four-wheel behavior, and an ElectricCar adds battery management. Each level builds on the previous one. Without multilevel inheritance, each new level would need to duplicate features from all ancestors.
Multilevel Inheritance occurs when a class is derived from another derived class, forming a chain. For example: Grandparent → Parent → Child. Each class in the chain inherits from its immediate predecessor and transitively inherits from all ancestors. This creates a layered hierarchy where each level adds specialized behavior.
Each link in the chain uses the standard extends keyword. When Child is instantiated, constructors fire in order: Grandparent() → Parent() → Child(). Method resolution walks up the chain: if Child doesn’t override a method, the JVM checks Parent, then Grandparent. The chain can be arbitrarily deep, but deep hierarchies are fragile and should be avoided.
- Layered abstraction: Each level adds specialized behavior on top of the previous
- Constructor chain: Constructors fire from topmost ancestor to most derived
- Transitive inheritance: Child inherits from ALL ancestors, not just the immediate parent
- Method resolution walks up: JVM checks child, then parent, then grandparent, etc.
- Deep hierarchy is a smell: 3+ levels often indicates over-engineering; favor composition
- Built from: Single Inheritance — each link is a single inheritance relationship
- Built from: Java Inheritance — extends mechanism drives the chain
- Contrasts with: Hierarchical Inheritance — chain vs fan-out
- Related: Inheritance Types — multilevel is one of the five inheritance types
- Deep hierarchy: 3+ levels of inheritance is often a design smell — favor composition over deep inheritance
- Fragile base class problem: Changes at the top of the chain can break classes multiple levels down