Concept · Intro

Inheritance

A subclass IS-A superclass — it inherits the parent’s fields and methods for free, and may add to or override them.

Asked atAmazonMicrosoftOracle

step 1 / 9

1/2A family tree

Vehicle

# speed: int

+ start()

+ stop()

Car

+ openTrunk()

Motorcycle

+ start()

Truck

+ load()

A family tree

 1class Vehicle {
 2    protected int speed;
 3    void start() { ... }
 4    void stop()  { ... }
 5}
 6 
 7class Car        extends Vehicle { void openTrunk(){...} }
 8class Truck      extends Vehicle { void load(){...} }
 9class Motorcycle extends Vehicle { void start(){...} }  // override

State

# protectedshared with children

✦

The base class holds what every vehicle shares: a protected speed field (#) and the start()/stop() operations. Define it once, here.