Multiple inheritance by Interface in Java

An interface contains variables and methods like a class but the methods in an interface are abstract by default unlike a class. Multiple inheritance by interface occurs if a class implements multiple interfaces or also if an interface itself extends multiple interfaces.

A program that demonstrates multiple inheritance by interface in Java is given as follows:

Example

<span class="kwd">interface</span><span class="pln"> </span><span class="typ">AnimalEat</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
   </span><span class="kwd">void</span><span class="pln"> eat</span><span class="pun">();</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">interface</span><span class="pln"> </span><span class="typ">AnimalTravel</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
   </span><span class="kwd">void</span><span class="pln"> travel</span><span class="pun">();</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">class</span><span class="pln"> </span><span class="typ">Animal</span><span class="pln"> </span><span class="kwd">implements</span><span class="pln"> </span><span class="typ">AnimalEat</span><span class="pun">,</span><span class="pln"> </span><span class="typ">AnimalTravel</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
   </span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> eat</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Animal is eating"</span><span class="pun">);</span><span class="pln">
   </span><span class="pun">}</span><span class="pln">
   </span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> travel</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Animal is travelling"</span><span class="pun">);</span><span class="pln">
   </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">Demo</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
   </span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> main</span><span class="pun">(</span><span class="typ">String</span><span class="pln"> args</span><span class="pun">[])</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
      </span><span class="typ">Animal</span><span class="pln"> a </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Animal</span><span class="pun">();</span><span class="pln">
      a</span><span class="pun">.</span><span class="pln">eat</span><span class="pun">();</span><span class="pln">
      a</span><span class="pun">.</span><span class="pln">travel</span><span class="pun">();</span><span class="pln">
   </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span>

Output

Animal is eating
Animal is travelling

Now let us understand the above program.

The interface AnimalEat and AnimalTravel have one abstract method each i.e. eat() and travel(). The class Animal implements the interfaces AnimalEat and AnimalTravel. A code snippet which demonstrates this is as follows:

<span class="kwd">interface</span><span class="pln"> </span><span class="typ">AnimalEat</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
   </span><span class="kwd">void</span><span class="pln"> eat</span><span class="pun">();</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">interface</span><span class="pln"> </span><span class="typ">AnimalTravel</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
   </span><span class="kwd">void</span><span class="pln"> travel</span><span class="pun">();</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">class</span><span class="pln"> </span><span class="typ">Animal</span><span class="pln"> </span><span class="kwd">implements</span><span class="pln"> </span><span class="typ">AnimalEat</span><span class="pun">,</span><span class="pln"> </span><span class="typ">AnimalTravel</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
   </span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> eat</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Animal is eating"</span><span class="pun">);</span><span class="pln">
   </span><span class="pun">}</span><span class="pln">
   </span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> travel</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Animal is travelling"</span><span class="pun">);</span><span class="pln">
   </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span>

In the method main() in class Demo, an object a of class Animal is created. Then the methods eat() and travel() are called. A code snippet which demonstrates this is as follows:

<span class="kwd">public</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">Demo</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
   </span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> main</span><span class="pun">(</span><span class="typ">String</span><span class="pln"> args</span><span class="pun">[])</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
      </span><span class="typ">Animal</span><span class="pln"> a </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Animal</span><span class="pun">();</span><span class="pln">
      a</span><span class="pun">.</span><span class="pln">eat</span><span class="pun">();</span><span class="pln">
      a</span><span class="pun">.</span><span class="pln">travel</span><span class="pun">();</span><span class="pln">
   </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span>