Unit 3 Cycle 1 Day 12: super Keyword in Constructors

February 18, 2026

Unit 3 Foundation (Cycle 1) Day 12 of 28 Foundation

super Keyword in Constructors

Section 3.14 — The super Keyword

Key Concept

When a subclass constructor executes, it must call a superclass constructor as its very first statement using super(arguments). If you do not explicitly call super(), Java automatically inserts a call to the no-argument superclass constructor. If the superclass does not have a no-argument constructor, the subclass must explicitly call a parameterized superclass constructor, or the code will not compile. The AP exam tests constructor chaining across inheritance hierarchies where constructors call super() with specific arguments.

Consider the following classes.

public class Vehicle { private int speed; public Vehicle(int s) { speed = s; } public int getSpeed() { return speed; } } public class Car extends Vehicle { private int doors; public Car(int s, int d) { super(s); doors = d; } }

What does new Car(60, 4).getSpeed() return?

Answer: (A) 60

super(s) calls Vehicle's constructor with s=60, setting speed=60. Car inherits getSpeed() from Vehicle, which returns 60.

Why Not the Others?

(B) 4 is the doors value, not speed. getSpeed() returns speed.

(C) The super constructor correctly sets speed to 60.

(D) The code compiles. super(s) correctly calls the parent constructor.

Common Mistake

super() must be the first statement in a subclass constructor. It passes arguments to the parent constructor. Without it, Java tries to call a no-arg parent constructor (which may not exist).