Multiple inheritance using interfaces in Java - Step-by-Step Execution

Concept Flow - Multiple inheritance using interfaces

Define Interface A

↓

Define Interface B

↓

Define Class C implements A, B

↓

Create object of Class C

↓

Call methods from A and B via C

This flow shows how a class can inherit from multiple interfaces and implement their methods.

Execution Sample

Java

interface A {
    void methodA();
}
interface B {
    void methodB();
}
class C implements A, B {
    public void methodA() { System.out.println("A method"); }
    public void methodB() { System.out.println("B method"); }
}
public class Test {
    public static void main(String[] args) {
        C obj = new C();
        obj.methodA();
        obj.methodB();
    }
}

This code shows a class C implementing two interfaces A and B, then calling their methods.

Execution Table

Step	Action	Evaluation	Result
1	Define interface A with methodA()	No output	Interface A ready
2	Define interface B with methodB()	No output	Interface B ready
3	Define class C implementing A and B	No output	Class C ready with methodA and methodB
4	Create object obj of class C	obj = new C()	Object obj created
5	Call obj.methodA()	Calls methodA()	Prints: A method
6	Call obj.methodB()	Calls methodB()	Prints: B method
7	End of main method	Program ends	Execution stops

💡 Program ends after calling both interface methods via class C object

Variable Tracker

Variable	Start	After Step 4	After Step 7
obj	null	Reference to new C()	Reference to new C() (no change)

Key Moments - 2 Insights

Why can class C implement both interfaces A and B without conflict?

Because interfaces only declare methods without implementation, class C provides its own implementations, avoiding conflicts as shown in execution_table steps 3 to 6.

What happens if class C does not implement one of the interface methods?

The code will not compile because Java requires all interface methods to be implemented, as implied by step 3 where class C is defined.

Visual Quiz - 3 Questions

Look at the execution_table, what is printed when obj.methodA() is called at step 5?

A B method

B No output

C A method

D Compilation error

💡 Hint

Refer to execution_table row 5 where obj.methodA() prints 'A method'

At which step is the object obj created?

A Step 3

B Step 4

C Step 5

D Step 6

💡 Hint

Check execution_table row 4 for object creation

If class C did not implement methodB(), what would happen?

A Compilation error

B Runtime error

C Program runs normally

D methodB() prints default message

💡 Hint

Recall key_moments about interface method implementation requirements

Concept Snapshot

Multiple inheritance in Java is done using interfaces.
A class can implement multiple interfaces.
Interfaces declare methods without bodies.
The class must implement all interface methods.
This avoids conflicts of multiple inheritance.
Use 'class C implements A, B' syntax.

Full Transcript

This example shows how Java uses interfaces to allow multiple inheritance. Interfaces A and B declare methods methodA and methodB. Class C implements both interfaces and provides method bodies. In main, an object of C calls both methods, printing their messages. This avoids the problems of multiple inheritance with classes by requiring explicit implementation. The execution table traces each step from interface definition to method calls. Variable tracking shows the object creation and usage. Key moments clarify why all methods must be implemented and how conflicts are avoided. The visual quiz tests understanding of method calls, object creation, and compilation rules. The snapshot summarizes the syntax and rules for multiple inheritance using interfaces in Java.