Java Multilevel Inheritance
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What is Multilevel Inheritance?
Multilevel inheritance chains classes together — C extends B, and B extends A — so C ends up inheriting from both its direct parent B and, transitively, from B's own parent A, forming a multi-tier hierarchy.
Example: What is Multilevel Inheritance?
class A {}
class B extends A {}
class C extends B {} // chain: C -> B -> A
public class Main {
public static void main(String[] args) {
C c = new C();
System.out.println(c instanceof A);
}
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Method Overriding in Multilevel Chains
Any class in the chain can override a method it inherited, and that override applies to it and everything below it in the chain, letting each tier customize behavior progressively as you move down the hierarchy.
Example: Method Overriding in Multilevel Chains
class A {
void show() { System.out.println("A"); }
}
class B extends A {
@Override
void show() { System.out.println("B"); }
}
class C extends B {
}
public class Main {
public static void main(String[] args) {
new C().show(); // uses B's override
}
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Constructor Chaining
Constructors run in order from the topmost ancestor down to the class actually being instantiated — A's constructor runs first, then B's, then C's — ensuring every level of the hierarchy gets to initialize its own portion of the object's state before the next level begins.
Example: Constructor Chaining
class A {
A() { System.out.println("A constructor"); }
}
class B extends A {
B() { System.out.println("B constructor"); }
}
class C extends B {
C() { System.out.println("C constructor"); }
}
public class Main {
public static void main(String[] args) {
new C();
}
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The super Keyword in Chains
super inside class C only reaches its immediate parent B, not grandparent A directly — if C needs something from A specifically, it has to go through B (assuming B exposes it), since super doesn't skip levels.
Example: The super Keyword in Chains
class A {
void show() { System.out.println("A"); }
}
class B extends A {
void showB() { super.show(); } // reaches only immediate parent A
}
class C extends B {
}
public class Main {
public static void main(String[] args) {
new C().showB();
}
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Instanceof in Multilevel Chains
An object created from the bottom class in the chain is considered an instance of every class above it, so instanceof checks against A, B, or C would all return true for that single object.
Example: Instanceof in Multilevel Chains
class A {}
class B extends A {}
class C extends B {}
public class Main {
public static void main(String[] args) {
C c = new C();
System.out.println(c instanceof A);
System.out.println(c instanceof B);
System.out.println(c instanceof C);
}
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