Method overriding in Java - Step-by-Step Execution

Concept Flow - Method overriding

Parent class defines method

↓

Child class defines method with same signature

↓

Create child class object

↓

Call method on child object

↓

Child's method runs, overrides parent

↓

Output from child method

Method overriding happens when a child class provides its own version of a method defined in its parent class. When called on a child object, the child's method runs instead of the parent's.

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 Test {
  public static void main(String[] args) {
    Parent obj = new Child();
    obj.greet();
  }
}

This code shows a parent and child class both with a greet method. The child overrides the parent's greet. When calling greet on a child object, the child's greet runs.

Execution Table

Step	Action	Object Type	Method Called	Output
1	Create Parent reference to Child object	Child	N/A	N/A
2	Call greet() on obj	Child	Child.greet()	Hello from Child
3	End of main method	N/A	N/A	N/A

💡 Program ends after main method finishes

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
obj	null	Child object reference	Child object reference	Child object reference

Key Moments - 2 Insights

Why does calling greet() on a Parent type variable run the Child's greet method?

Because the actual object is of Child type (see execution_table step 1 and 2), Java uses the object's real type to decide which method to run, not the variable's declared type.

What happens if the Child class does not override greet()?

Then calling greet() on the Child object runs the Parent's greet method, because no overriding method exists in Child (not shown in table but implied).

Visual Quiz - 3 Questions

Look at the execution_table at step 2, which method is called when obj.greet() runs?

A Parent.greet()

B Child.greet()

C Both Parent.greet() and Child.greet()

D No method is called

💡 Hint

Check the 'Method Called' column in execution_table step 2

At which step is the Child object created and assigned to obj?

A Step 3

B Step 2

C Step 1

D No object is created

💡 Hint

Look at the 'Action' and 'Object Type' columns in execution_table step 1

If obj was declared as Parent and assigned a Parent object, which greet() method would run?

A Parent.greet()

B Child.greet()

C Both methods

D No method

💡 Hint

Refer to key_moments explanation about object type deciding method call

Concept Snapshot

Method overriding lets a child class provide its own version of a method from the parent class.
When calling the method on a child object, the child's method runs, even if the variable type is the parent.
The method signature must match exactly.
This enables polymorphism and dynamic method dispatch in Java.

Full Transcript

This example shows method overriding in Java. The Parent class has a greet method. The Child class extends Parent and overrides greet with its own version. In main, a Parent type variable obj holds a Child object. When obj.greet() is called, Java runs Child's greet method because the actual object is Child. The execution table traces creating the Child object, calling greet, and the output. The variable tracker shows obj pointing to the Child object throughout. Key moments clarify why the Child method runs despite the Parent type variable. The quiz tests understanding of method calls and object types. The snapshot summarizes the key points about method overriding and dynamic dispatch.