Practice›Java Fundamentals›Module 7. Inheritance & Polymorphism›7.2 Overriding

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7.2 Overriding — the toString method

Lesson

Making an object printable

Every object has a toString() method (inherited from Object) that println uses to turn it into text. By default it returns something unhelpful — the class name and a hash code. Override toString() to return a readable description, and System.out.println(obj) will use it automatically.

Worked example

class Dog extends Animal {
    @Override
    public String toString() {
        return "Dog(" + getName() + ")";
    }
}

Dog d = new Dog("Rex");
System.out.println(d);   // "Dog(Rex)" — println calls toString()

You do not call toString() yourself; println calls it for you.

▶ Try it: run this — printing the Dog object uses your toString().

class Animal {
    private String name;
    public Animal(String name) { this.name = name; }
    public String getName() { return name; }
    public String describe() { return name + " is an animal"; }
}
class Dog extends Animal {
    public Dog(String name) { super(name); }
    @Override
    public String toString() { return "Dog(" + getName() + ")"; }
}
public class Main {
    public static void main(String[] args) {
        Dog d = new Dog("Rex");
        System.out.println(d);
    }
}

Which method does println use to turn an object into text?

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By default (not overridden), toString() returns...

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Type exactly what this program prints.

class Animal { String n; Animal(String x){n=x;} String getName(){return n;} }
class Dog extends Animal { Dog(String x){super(x);} public String toString(){return "Dog("+getName()+")";} }
public class Main { public static void main(String[] a){
    System.out.println(new Dog("Rex"));
}}

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System.out.println(myDog) with an overridden toString() prints...

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True or false?

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