How to write interfaces in java or Android?

By | February 7, 2013

This tutorial is about how to use interfaces in java or Android.

What is an Interface?

An interface is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface.

An interface is not a class. Writing an interface is similar to writing a class, but they are two different concepts. A class describes the attributes and behaviors of an object. An interface contains behaviors that a class implements.

Unless the class that implements the interface is abstract, all the methods of the interface need to be defined in the class.

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An interface is similar to a class in the following ways:

  • An interface can contain any number of methods.

  • An interface is written in a file with a .java extension, with the name of the interface matching the name of the file.

  • The bytecode of an interface appears in a .class file.

  • Interfaces appear in packages, and their corresponding bytecode file must be in a directory structure that matches the package name.

However, an interface is different from a class in several ways, including:

  • You cannot instantiate an interface.

  • An interface does not contain any constructors.

  • All of the methods in an interface are abstract.

  • An interface cannot contain instance fields. The only fields that can appear in an interface must be declared both static and final.

  • An interface is not extended by a class; it is implemented by a class.

  • An interface can extend multiple interfaces.

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Sample Code

Here I will show you how to do it in Android or Java.
This example is for Android.

So can we start.

This is the interface that I am going to implement.

Interface Class

package com.coderzheaven.interfacetest1;

public interface MyTestInterface {

	void testFunctionOne();

	void testFunctionTwo();


Now we will write the activity that implements the above interface.

package com.coderzheaven.interfacetest1;

import android.os.Bundle;

public class MainActivity extends Activity implements MyTestInterface {

	protected void onCreate(Bundle savedInstanceState) {

	public void testFunctionOne() {
		System.out.println("Print from testFunctionOne in the Interface");

	public void testFunctionTwo() {
		System.out.println("Print from testFunctionTwo in the Interface");

Ok Done. Go on and Run it.

3 thoughts on “How to write interfaces in java or Android?

  1. Krishh

    ur code is flawless .But interface methods are not executing.

    Can you please provide code of how we can transfer data between two activities using interface .

  2. Rakesh R

    Useful tutorial..
    I suggest to beginners to use Toast instead of SOP…


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