How to Implement an Interface in Java

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In Brief...

An implementation of an interface is a Java program that references the interface using the implements keyword. The program is required to provide method logic for all non-default methods. Optionally, the program can provide an implementation of a default method defined in the interface. To create an interface implementation in Java, follow these six steps.

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Instructions

  1. Open your text editor and type in the following Java statements:
    Java Source for Interface Definition
    The interface defines three methods for displaying a name and optionally a job title. One method is a default method that contains implementation logic. The remaining two methods do not include implementation logic.
  2. Save your file as CreateAnInterfaceDefinition.java.
  3. Open a command prompt and navigate to the directory containing your Java program. Then type in the command to compile the source and hit Enter.
    Compile Source for Interface Definition
    The interface is now ready to be implemented by a Java program.
  4. Open your text editor and type in the following Java statements:
    Java Source for Interface Implementation
    The Java program declares that it will implement the interface by using the implements keyword. The program is now obligated to provide Java code for the two non-default methods. Accordingly, implementations of the methods are provided.
  5. Save your file as CreateAnInterfaceDefinitionImpl.java. The suffix Impl is a standard way of advertising that this Java program is an implementation of CreateAnInterfaceDefinition.java.
  6. Open a command prompt and navigate to the directory containing your Java program. Then type in the command to compile the source and hit Enter.
    Compile Source for Interface Implementation
    The interface implementation can now be instantiated by a Java class so that the methods can be called.

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Author: Stephen Withrow

Stephen has over 30 years' experience in training, development, and consulting in a variety of technology areas including Java, C, C++, XML, JavaScript, AJAX, Tomcat, JBoss, Oracle, and DB2. His background includes design and implementation of business solutions on client/server, Web, and enterprise platforms. Stephen is a published writer in both technical and non-technical endeavors. Stephen received an undergraduate degree in Computer Science and Physics from Florida State University.

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