If a class has at least one abstract method, then the class must be declared abstract.

Java Programming Language Polymorphism in Java (Article) Polymorphism in Java (Program)

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Program:

<span class="pln"> </span><span class="kwd">abstract</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">Human</span><span class="pun">{</span><span class="pln">
  </span><span class="kwd">abstract</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> mother</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">Woman</span><span class="pln"> </span><span class="kwd">extends</span><span class="pln"> </span><span class="typ">Human</span><span class="pun">{</span><span class="pln">
	</span><span class="kwd">void</span><span class="pln"> mother</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">"I am Your Mother"</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">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="typ">Human</span><span class="pln"> obj </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Woman</span><span class="pun">();</span><span class="pln">
	 obj</span><span class="pun">.</span><span class="pln">mother</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>

Output:

I am Your Mother
Press any key to continue . . .

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