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copied!<p>The <code>abstract</code> class is not real implementation class. It may contain <code>abstract</code> methods and doesnot need to <code>implement</code> the methods from the <code>interface</code>. It is concern of the REAL implementing class to define the abstract/interface methods.</p> <p>See this difference between abstract class and interface</p> <pre><code>Interface: public interface InterfaceClass { void interfaceMethod(); //no method definition } //Abstract Class implementing InterfaceClass abstract class AbsClass implements InterfaceClass{ abstract void abstractMethod(); public void doSomethingCommon() { System.out.println("Abstract class may contain method definition"); } //no need to implement methods of InterfaceClass because AbsClass is abstract } </code></pre> <p>And here is real class that extends <code>AbsClass</code>: <strong>Its duty of RealClass to define all abstract methods and interface methods.</strong> Additionally, it may <code>override</code> the defined methods in <code>abstract</code> class as well.</p> <pre><code>public class RealClass extends AbsClass{ @Override public void interfaceMethod() { //implement interface method here } @Override void abstractMethod() { } // you may override the doSomethingCommon() of AbsClass too @Override public void doSomethingCommon() { // TODO Auto-generated method stub super.doSomethingCommon(); } } </code></pre> <p>Why there is no compile time error on <code>AbsClass</code>: We cannot create instances of abstract class. That's why there is no meaning of displaying error at compile time.</p>

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