Interface with two implementations

Classes & objects · Beginner · 14 min · Runs in your Salesforce Developer org · Free

Define a `Notifier` interface with one method, then write two classes that implement it. `EmailNotifier` prefixes the message with `EMAIL: `, and `SlackNotifier` prefixes it with `SLACK: `. Each class provides its own body for the same method signature.

Lesson

Why this matters

Salesforce code often has to support more than one channel: email, Slack, chatter, SMS. If callers depend on a concrete class (EmailNotifier), swapping channels means rewriting them. An interface is a contract that says "anything with a send(String) method is a Notifier." Callers depend on the contract, not on any one class.

The smallest working example

public interface Notifier {
    String send(String message);
}

public class EmailNotifier implements Notifier {
    public String send(String message) {
        return 'EMAIL: ' + message;
    }
}

new EmailNotifier().send('Hi') returns EMAIL: Hi.

Name the parts

**interface Notifier** lists method signatures with no body. The semicolon after send(String message); ends the signature.
**implements Notifier** on a class is a promise to provide every method on the interface.
Interface methods have no modifier. Inside the class, the exposed method must be **public**.
Each class picks its own prefix and returns the result; the interface itself knows nothing about prefixes.

A common wrong version

public interface Notifier {
    public String send(String message);   // modifier is not allowed
}

public class EmailNotifier implements Notifier {
    String send(String message) {         // missing `public`
        return 'EMAIL: ' + message;
    }
}

Two mistakes. The interface method must have no modifier, and the class method must be public so callers can reach it.

The fix

Strip the modifier from the interface signature and mark the class method public:

public interface Notifier {
    String send(String message);
}

public class SlackNotifier implements Notifier {
    public String send(String message) {
        return 'SLACK: ' + message;
    }
}

Now you try

Fill in Notifier with one method String send(String message);. Make EmailNotifier and SlackNotifier return the message with the matching prefix. Keep every type name and signature; the grader creates instances by name and calls send.

Learn more

Apex Developer Guide: Interfaces

The challenge

Finish the Notifier interface and its two implementations.

Examples:

new EmailNotifier().send('Hi') returns EMAIL: Hi
new SlackNotifier().send('Hi') returns SLACK: Hi
new EmailNotifier().send('') returns EMAIL:

Requirements:

new EmailNotifier().send('Hi') should be EMAIL: Hi.
new SlackNotifier().send('Hi') should be SLACK: Hi.
new EmailNotifier().send('') should be EMAIL: .
new SlackNotifier().send('Deploy done') should be SLACK: Deploy done.
new EmailNotifier().send('Order #42') should be EMAIL: Order #42.

Starter code

public interface Notifier {
}

public class EmailNotifier implements Notifier {
}

public class SlackNotifier implements Notifier {
}

Related drills

Try this drill free

You write the Apex yourself. ApexSensei runs it and tells you what passed and what did not.

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