Super keyword in Java - Step-by-Step Execution

Concept Flow - Super keyword

Create Subclass Object

↓

Call Subclass Constructor

↓

Inside Subclass Constructor

↓

Use super() to call Parent Constructor

↓

Parent Constructor runs

↓

Return to Subclass Constructor

↓

Complete Subclass Constructor

↓

Object Ready

Shows how creating a subclass object calls the subclass constructor, which uses super() to run the parent constructor first, then finishes.

Execution Sample

Java

class Parent {
  Parent() { System.out.println("Parent constructor"); }
}
class Child extends Parent {
  Child() { super(); System.out.println("Child constructor"); }
}
new Child();

Creates a Child object that calls Parent constructor first using super(), then runs Child constructor.

Execution Table

Step	Action	Output	Notes
1	Create Child object		Start creating Child instance
2	Call Child constructor		Child() starts
3	Call super() inside Child constructor	Parent constructor	Parent() runs first
4	Return to Child constructor	Child constructor	Child() continues
5	Child constructor ends		Object creation complete

💡 Child object fully created after Parent and Child constructors run

Variable Tracker

Variable	Start	After Step 3	After Step 5
this (Child object)	null	partially constructed (Parent part done)	fully constructed

Key Moments - 3 Insights

Why does the Parent constructor run before the Child constructor finishes?

Because super() in the Child constructor calls the Parent constructor first, as shown in step 3 of the execution_table.

What happens if we omit super() in the Child constructor?

Java inserts super() automatically if no other constructor call is present, so Parent constructor still runs first.

Can super() be called after some code in the Child constructor?

No, super() must be the first statement in the Child constructor, or the code will not compile.

Visual Quiz - 3 Questions

Look at the execution_table, what is printed at step 3?

A No output

B Child constructor

C Parent constructor

D Error

💡 Hint

Check the Output column for step 3 in the execution_table

At which step does the Child constructor print its message?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the Output and Notes columns for step 4 in the execution_table

If super() was missing in the Child constructor, what would happen?

A Parent constructor would not run

B Parent constructor runs automatically

C Compilation error

D Child constructor runs twice

💡 Hint

Recall the key_moments about implicit super() call

Concept Snapshot

Super keyword in Java:
- Used in subclass to call parent class constructor or methods
- super() must be first line in subclass constructor
- Ensures parent class is initialized before subclass
- Helps access overridden methods or hidden variables
- If omitted, Java inserts super() automatically in constructor

Full Transcript

This visual trace shows how the super keyword works in Java. When creating a Child object, the Child constructor runs. Inside it, super() calls the Parent constructor first, printing "Parent constructor". Then control returns to the Child constructor, which prints "Child constructor". This order ensures the parent part of the object is set up before the child part. The variable tracker shows the Child object is partially constructed after the Parent constructor runs, and fully constructed at the end. Key points include that super() must be the first statement in the constructor, and if omitted, Java adds it automatically. The quizzes test understanding of the print order and behavior if super() is missing.