Inheritance

Sometimes you want a class that's basically another class, but with extras. In Java, a class can inherit from another using the keyword extends

class Criminal {
    String name;

    Criminal(String name) {
        this.name = name;
    }

    void speak() {
        System.out.println("...");
    }
}

class Driver extends Criminal {
    Driver(String name) {
        super(name);
    }

    void speak() {
        System.out.println("I'm the driver " + name + ", get in the car!");
    }
}

The Driver class inherits everything from Criminal: its name field, its constructor logic, everything. Then it overrides the speak() method to do its own thing. This is inheritance, one of the biggest ideas in Java

An example from Vice City: Tommy Vercetti is a criminal (the parent class). Lance Vance is also a criminal, but he's a specific kind: a backstabbing criminal. He extends the base criminal class with his own special behavior (betrayal). He still has all the base criminal abilities, plus his own twist

The super keyword is how a child talks to its parent. When Driver calls super(name), it's saying "hey Criminal, run YOUR constructor with this name." The parent constructor sets this.name = name, and now the driver has a name

You must call super(...) in the child constructor if the parent doesn't have a no-argument constructor. Java won't let you skip it: the parent needs to be set up before the child can add its own stuff

class Criminal {
    String name;
    int respect;

    Criminal(String name, int respect) {
        this.name = name;
        this.respect = respect;
    }
}

class Boss extends Criminal {
    Boss(String name) {
        super(name, 100);  // a boss always starts with max respect
    }
}

A child class can also add new fields and methods that the parent doesn't have

class Criminal {
    String name;

    Criminal(String name) {
        this.name = name;
    }

    void speak() {
        System.out.println("...");
    }
}

class Driver extends Criminal {
    String car;

    Driver(String name, String car) {
        super(name);
        this.car = car;
    }

    void speak() {
        System.out.println("I'm the driver " + name);
    }

    void drive() {
        System.out.println(name + " drives a " + car + "!");
    }
}

Now Driver has everything Criminal has, PLUS a car field and a drive() method. The parent Criminal doesn't know about driving, that's the driver's own thing

Here's a full runnable example

class Criminal {
    String name;

    Criminal(String name) {
        this.name = name;
    }

    void speak() {
        System.out.println("Some random Vice City criminal");
    }
}

class Driver extends Criminal {
    Driver(String name) {
        super(name);
    }

    void speak() {
        System.out.println("I'm the driver " + name);
    }
}

class Gunman extends Criminal {
    Gunman(String name) {
        super(name);
    }

    void speak() {
        System.out.println("I'm the gunman " + name);
    }
}

public class Main {
    public static void main(String[] args) {
        Driver d = new Driver("Tommy");
        Gunman g = new Gunman("Lance");
        d.speak();
        g.speak();
    }
}

Output

I'm the driver Tommy
I'm the gunman Lance

Mission: Tommy's Crew

Tommy's crew has different roles, but they're all criminals. Each one introduces themselves their own way. Build the inheritance hierarchy.

Create a Criminal class with a name field, a constructor, and a speak() method that prints "...". Then create two child classes:

1. Driver extends Criminal and overrides speak() to print "I'm the driver " + name
2. Gunman extends Criminal and overrides speak() to print "I'm the gunman " + name

In main, store the two names in variables name1 and name2 (start with "Tommy" and "Lance"). Create a Driver from name1 and a Gunman from name2, then call speak() on both.

Example

I'm the driver Tommy
I'm the gunman Lance