Interface declaration in Java - Step-by-Step Execution

Concept Flow - Interface declaration

Start

↓

Write 'interface' keyword

↓

Name the interface

↓

Open curly brace '{'

↓

Declare method signatures (no body)

↓

Close curly brace '}'

↓

Interface ready to be implemented

↓

End

This flow shows how to declare an interface in Java step-by-step, from keyword to method signatures and closing brace.

Execution Sample

Java

public interface Animal {
    void sound();
    void eat();
}

Declares an interface named Animal with two method signatures: sound and eat.

Execution Table

Step	Code Part	Action	Result
1	public interface Animal {	Declare interface named Animal	Interface Animal created
2	void sound();	Declare method signature sound	Method sound() added to interface
3	void eat();	Declare method signature eat	Method eat() added to interface
4	}	Close interface declaration	Interface Animal declaration complete

💡 Interface declaration ends after closing brace '}'

Variable Tracker

Element	Start	After Step 1	After Step 2	After Step 3	Final
Interface Name	none	Animal	Animal	Animal	Animal
Methods	none	none	sound()	sound(), eat()	sound(), eat()

Key Moments - 2 Insights

Why don't interface methods have a body?

Interface methods only declare what should be done, not how. This is shown in steps 2 and 3 where methods have no body, only signatures.

Can we create an object of an interface directly?

No, interfaces cannot be instantiated. They only define method signatures to be implemented by classes. This is implied after step 4 when the interface is ready but not an object.

Visual Quiz - 3 Questions

Look at the execution table, what is declared at step 1?

A A method named sound

B A class named Animal

C An interface named Animal

D An object of Animal

💡 Hint

Check the 'Code Part' and 'Action' columns in row 1 of the execution table.

At which step are method signatures added to the interface?

A Step 2 and Step 3

B Step 1

C Step 4

D No methods are added

💡 Hint

Look at the 'Action' column for steps 2 and 3 in the execution table.

According to the variable tracker, how many methods does the interface have after step 3?

A 1

B 2

C 0

D 3

💡 Hint

Check the 'Methods' row in the variable tracker after step 3.

Concept Snapshot

Interface declaration syntax:
public interface InterfaceName {
    returnType methodName();
    // method signatures only, no bodies
}
Interfaces define method signatures to be implemented by classes.
They cannot be instantiated directly.

Full Transcript

This visual execution shows how to declare an interface in Java. First, the keyword 'interface' is used with a name. Then method signatures are declared without bodies. Finally, the interface declaration is closed with a brace. The interface holds method signatures but no implementations. It cannot be instantiated directly but is used by classes to implement the declared methods.