Parent and child classes in Java - Step-by-Step Execution

Concept Flow - Parent and child classes

Define Parent Class

↓

Define Child Class extends Parent

↓

Create Child Object

↓

Child inherits Parent's properties

↓

Child can use or override Parent methods

↓

Use Child object to call methods

↓

End

Shows how a child class inherits from a parent class, can use or change its methods, and how objects of the child class behave.

Execution Sample

Java

class Parent {
  void greet() {
    System.out.println("Hello from Parent");
  }
}

class Child extends Parent {
  void greet() {
    System.out.println("Hello from Child");
  }
}

public class Main {
  public static void main(String[] args) {
    Child c = new Child();
    c.greet();
  }
}

Defines a parent and child class where child overrides a method; creates child object and calls greet.

Execution Table

Step	Action	Evaluation	Result
1	Define Parent class with greet()	No output	Parent class ready
2	Define Child class extends Parent with greet()	No output	Child class ready, overrides greet()
3	Create Child object c	c is new Child()	Object c created
4	Call c.greet()	Calls Child's greet()	Prints: Hello from Child
5	End of program	No more instructions	Program stops

💡 Program ends after calling greet() on Child object

Variable Tracker

Variable	Start	After Step 3	Final
c	undefined	Child object created	Child object exists

Key Moments - 2 Insights

Why does c.greet() print 'Hello from Child' and not 'Hello from Parent'?

Because the Child class overrides the greet() method. Execution_table step 4 shows c.greet() calls Child's greet(), so Child's version runs.

Does the Child class have access to Parent's greet() method?

Yes, but since Child overrides greet(), its own version is used. If Child did not override greet(), Parent's greet() would run.

Visual Quiz - 3 Questions

Look at the execution table, what is printed when c.greet() is called at step 4?

A "Hello from Child"

B "Hello from Parent"

C Nothing is printed

D Compilation error

💡 Hint

See execution_table row 4 where c.greet() calls Child's greet() and prints the message.

At which step is the Child object created?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Check execution_table row 3 where the Child object c is created.

If the Child class did not override greet(), what would c.greet() print?

A "Hello from Child"

B "Hello from Parent"

C Compilation error

D No output

💡 Hint

Since Child inherits Parent, without override, Parent's greet() runs (see concept explanation).

Concept Snapshot

Parent and child classes in Java:
- Use 'class Child extends Parent' to inherit.
- Child inherits Parent's methods and fields.
- Child can override Parent methods to change behavior.
- Create objects of Child to use inherited or overridden methods.
- Method calls on Child objects use Child's version if overridden.

Full Transcript

This example shows how a child class inherits from a parent class in Java. First, the Parent class is defined with a greet() method that prints a message. Then, the Child class extends Parent and overrides the greet() method with its own message. When we create an object c of type Child and call c.greet(), the program runs the Child's greet() method, printing 'Hello from Child'. This demonstrates inheritance and method overriding. The execution table traces each step: defining classes, creating the object, calling the method, and ending the program. The variable tracker shows the Child object c being created and existing. Key moments clarify why the Child's greet() runs and that Child inherits Parent's methods. The quiz tests understanding of method overriding, object creation, and inheritance behavior. This is a basic but important concept in object-oriented programming.