[Java] About interface

I'm learning Java and would like to summarize one of the points (?) Interface that is easy to trip over.

An example of interface on Android is summarized in another article.

-[Android] interface example

If you want to deepen your understanding of interface in Android application programming, I think it's a good idea to create your own listener.

-Android Countdown

About interface

How to write an interface.

Runnable in java.lang is an example interface.


package java.lang;

 * Represents a command that can be executed. Often used to run code in a
 * different {@link Thread}.
public interface Runnable {

     * Starts executing the active part of the class' code. This method is
     * called when a thread is started that has been created with a class which
     * implements {@code Runnable}.
    public void run();

To make it simple


public interface Runnable {
    public void run();

It will be like this.

A refreshing introduction to Java In the second edition, it is sometimes explained by the expression "abstract class in abstract class".

Two conditions treated as an interface

  1. All methods are abstract methods
  2. Basically it has no fields

Abstract method

Contents of processing (without {/ * ... processing ... * /}) Method.


public void run();

Part of.

About interface fields

When you declare a field in the interface, it is treated as if you declared a constant in public static final.

Instance generation

Abstract methods must be ** always overridden **, so when instantiating ╩╗interface`,


Runnable runnable = new Runnable() {
    public void run() {


In this way, you will create an instance while overriding the run () method.


--Introduction to Java that you can understand clearly 2nd edition -Interface Runnable

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