toString()

What happens when you try to print an object directly?

class Car {
    String make;
    int year;

    Car(String make, int year) {
        this.make = make;
        this.year = year;
    }
}

public class Main {
    public static void main(String[] args) {
        Car c = new Car("Infernus", 1986);
        System.out.println(c);
    }
}

Output

Car@6d06d69c

That's... not helpful. Java doesn't know how you want your object displayed, so it gives you the class name and some memory address. To fix this, we override a special method called toString()

Overriding toString()

Every object in Java has a toString() method (inherited from a base class called Object). By default it prints that ugly gibberish. But you can override it: write your own version:

class Car {
    String make;
    int year;

    Car(String make, int year) {
        this.make = make;
        this.year = year;
    }

    @Override
    public String toString() {
        return make + " (" + year + ")";
    }
}

public class Main {
    public static void main(String[] args) {
        Car c = new Car("Infernus", 1986);
        System.out.println(c);
    }
}

Output

Infernus (1986)

Now when you print the object, Java calls your toString() and uses whatever string you return

The @Override Annotation

That @Override thing above the method is an annotation. It tells Java "I'm intentionally replacing a method from the parent class." It's optional but strongly recommended because:

• If you accidentally misspell the method (like tostring() with a lowercase S), Java will give you an error instead of silently creating a new method that does nothing
• It makes your code clearer to anyone reading it

public class Main {
    @Override
    public String toString() {   // Java checks: does the parent have toString()? Yes. Good.
        return "something";
    }
}

toString() Is Called Automatically

Java calls toString() in several situations automatically:

class Weapon {
    String name;
    int damage;

    Weapon(String name, int damage) {
        this.name = name;
        this.damage = damage;
    }

    @Override
    public String toString() {
        return name + " (damage: " + damage + ")";
    }
}

public class Main {
    public static void main(String[] args) {
        Weapon w = new Weapon("Katana", 75);

        // All of these call toString() automatically:
        System.out.println(w);                    // direct print
        System.out.println("Weapon: " + w);       // string concatenation
        String s = "Got a " + w;                   // building a string
        System.out.println(s);
    }
}

Output

Katana (damage: 75)
Weapon: Katana (damage: 75)
Got a Katana (damage: 75)

Whenever Java needs to turn your object into a String, it calls toString(). Concatenation with + does this, println() does this. It's everywhere

A More Detailed Example

Tommy Vercetti's squad needs proper string representations:

class GangMember {
    String name;
    String role;
    int respect;

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

    @Override
    public String toString() {
        return name + " - " + role + " (Respect: " + respect + ")";
    }
}

public class Main {
    public static void main(String[] args) {
        GangMember t = new GangMember("Tommy Vercetti", "Boss", 100);
        GangMember l = new GangMember("Lance Vance", "Partner", 60);
        System.out.println(t);
        System.out.println(l);
    }
}

Output

Tommy Vercetti - Boss (Respect: 100)
Lance Vance - Partner (Respect: 60)

Mission: Tommy's Garage

Tommy keeps his cars in a garage and wants each one to print nicely when he prints it, without building the string by hand every time

Create a Car class with a make (String) field and a year (int) field. Write a constructor and override toString() to return the make, then (, the year, and ), for example Infernus (1986)

In main, first store the values in local variables: make1 and year1 for the first car, make2 and year2 for the second. Then create two cars from those variables and print them directly with System.out.println

Example: Infernus from 1986 and Cheetah from 1984

Infernus (1986)
Cheetah (1984)