How to Call an Interface Method in Java

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In Brief...

In order to call an interface method from a Java program, the program must first instantiate the interface implementation program. A method can then be called using the implementation object. To learn how to call an interface method in Java, follow these 10 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. In your command prompt, 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.
  7. Return to your text editor. You will now type in the Java statements for the program that calls the interface methods:
    Java Source for Calling Interface Methods
    The program instantiates the interface implementation. Next, each of the methods defined in the interface is called.
  8. Save your file as CallAnInterfaceMethod.java.
  9. Return to the 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 Calling Interface Implementation
  10. Type in the command to run your program and hit Enter.
    Run for Interface Implementation
    The output demonstrates that each interface method has been called.

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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