Java implements keyword examples

In Java, the implements keyword is used to make a class adheres to contract defined by an interface. The implemented class must provide concrete implementation for the methods defined by the interface. If not, the class must be abstract.

The following example illustrates a class implements an interface and provides detailed implementation for the interface's methods:

interface Vehicle {
    void start();
    void stop();
}

class Car implements Vehicle {
    void start() {
        // starts the engine
    }
    
    void stop() {
        // stop the engine    
    }
}

Unlike extends keyword, a class can implement multiple interfaces. The interface names are separated by commas. For example:

interface Peson { }
interface Employee {}
class Director implements Person, Employee { }    

If the implemented class does not provide implementation for the interface's methods, the class must be abstract. For example:

interface Animal {
    void eat();
}

abstract class Reptile implements Animal {
    abstract void crawl();
}

In that case, the first non-abstract class must implement the method. For example:

class Crocodile extends Reptile {
    void eat() {
        // eats
    }
    
    void crawl() {
        // crawls
    }
}

Related keyword: class, interface, abstract and extends. See all keywords in Java.

Related Topics:

• Understand Inheritance in Java

Other Recommended Tutorials:

• 9 Rules about Constructors in Java
• 12 Rules and Examples About Inheritance in Java
• 12 Rules of Overriding in Java You Should Know
• 10 Java Core Best Practices Every Java Programmer Should Know
• Understand Interfaces in Java
• Understand how variables are passed in Java
• Understand encapsulation in Java

About the Author:

Nam Ha Minh is certified Java programmer (SCJP and SCWCD). He began programming with Java back in the days of Java 1.4 and has been passionate about it ever since. You can connect with him on Facebook and watch his Java videos on YouTube.