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Answer and Explanation

Question 7

What output is produced by the program shown in Listing 7 ?

  • A. Compiler Error
  • B. Runtime Error
  • C. A-intfcMethodX B-intfcMethodX
  • D. None of the above.

Listing 7 . Listing for Question 7.

public class Ap137{ public static void main(String args[]){new Worker().doIt(); }//end main()}//end class Ap137 class Worker{void doIt(){ Object[]myArray = new Object[2];myArray[0] = new A();myArray[1] = new B();for(int i=0;i<myArray.length;i++){ ((X)myArray[i]).intfcMethodX(); }//end for loopSystem.out.println(""); }//end doIt()}// end class Worker class Base{public void inherMethod(){ System.out.print("Base ");}//end inherMethod() }//end class Baseclass A extends Base implements X{ public void inherMethod(){System.out.print( " A-inherMethod ");}//end inherMethod()public void intfcMethodX(){ System.out.print("A-intfcMethodX "); }//end intfcMethodX()}//end class A class B extends Base implements X{public void inherMethod(){ System.out.print(" B-inherMethod "); }//end inherMethod()public void intfcMethodX(){System.out.print( "B-intfcMethodX ");}//end intfcMethodX() }//end class Binterface X{ public void intfcMethodX();}//end X

Answer and Explanation

Question 8

What output is produced by the program shown in Listing 8 ?

  • A. Compiler Error
  • B. Runtime Error
  • C. A-intfcMethodX B-intfcMethodX
  • D. None of the above.

Listing 8 . Listing for Question 8.

public class Ap138{ public static void main(String args[]){new Worker().doIt(); }//end main()}//end class Ap138 class Worker{void doIt(){ X[]myArray = new X[2];myArray[0] = new A();myArray[1] = new B();for(int i=0;i<myArray.length;i++){ myArray[i].intfcMethodX(); }//end for loopSystem.out.println(""); }//end doIt()}// end class Worker class Base{public void inherMethod(){ System.out.print("Base ");}//end inherMethod() }//end class Baseclass A extends Base implements X{ public void inherMethod(){System.out.print( " A-inherMethod ");}//end inherMethod()public void intfcMethodX(){ System.out.print("A-intfcMethodX "); }//end intfcMethodX()}//end class A class B extends Base implements X{public void inherMethod(){ System.out.print(" B-inherMethod "); }//end inherMethod()public void intfcMethodX(){System.out.print( "B-intfcMethodX ");}//end intfcMethodX() }//end class Binterface X{ public void intfcMethodX();}//end X

Answer and Explanation

Question 9

What output is produced by the program shown in Listing 9 ?

  • A. Compiler Error
  • B. Runtime Error
  • C. Base A B
  • D. None of the above.
Listing 9 . Listing for Question 9.
public class Ap139{ public static void main(String args[]){new Worker().doIt(); }//end main()}//end class Ap139 class Worker{void doIt(){ Base myVar = new Base();myVar.test(); myVar = new A();myVar.test(); myVar = new B();myVar.test(); System.out.println("");}//end doIt() }// end class Workerclass Base{ public void test(){System.out.print("Base "); }//end test()}//end class Base class A extends Base implements X,Y{public void test(){ System.out.print("A ");}//end test() }//end class Aclass B extends Base implements X,Y{ public void test(){System.out.print("B "); }//end test()}//end class B interface X{public void test(); }//end Xinterface Y{ public void test();}//end Y

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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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