Understanding the 'implements' Keyword in Java

The 'implements' keyword in Java is used to include an interface in a class. This allows the class to inherit the abstract methods of the interface.

Explanation and Examples

In Java, an interface serves as a prototype or contract which defines a set of methods that a class must have if it implements that interface. In this way, an interface is similar to a class, but it is a collection of abstract methods. These methods are declared but they do not have a body.

When a class uses the 'implements' keyword followed by an interface name, it means the class is making a commitment to implement all the methods defined in that interface.

Consider the following example:

interface Animal {
    void eat();
    void sleep();
}

class Dog implements Animal {
    public void eat() {
        System.out.println("Dog eats");
    }

    public void sleep() {
        System.out.println("Dog sleeps");
    }
}

In the above code, Dog is a class that implements the Animal interface. Since Dog is using the 'implements' keyword with Animal, it must provide the implementation for all methods declared in the Animal interface, in this case, eat() and sleep().

Best Practices and Insights

When using the 'implements' keyword to include an interface in a Java class, consider the following practices and insights:

1. Adherence to the contract: When a class implements an interface, it is like signing a contract committing that the class will provide specific behaviors specified in the interface.

2. Multiple Interfaces: A class in Java can implement multiple interfaces. This is useful in situations where a class needs to exhibit behaviors defined by more than one interface. It uses a comma-separated list of interfaces to do so: class MyClass implements Interface1, Interface2 {...}

3. Coding to an interface, not an implementation: A key principle in object-oriented design is "program to an interface, not an implementation." This means that the variables in a program should be declared to be of the interface type, not the actual implementation type. This promotes flexibility and allows the specific implementation to be chosen at runtime.

Indeed, the 'implements' keyword is a powerful tool in Java, facilitating adherence to interfaces and enabling a form of multiple inheritance in a class hierarchy. By understanding how it works, programmers can write more flexible and maintainable code.