Java MCQ Multiple Choice Question and answer

Java Programming OOPs

Java MCQ Multiple Choice Question and answer

1.	The default value of a static integer  variable of a class in Java is, (a)  0                       (b)  1                       (c)  Garbage value   (d)  Null    (e)  -1. Answer : (a) Reason:  The default value of a static integer  variable of a class in Java is 0.
2.	What will be printed as the output of the following program?                   public class testincr                   {                   public static void main(String args[])                   {                      int i = 0;                      i = i++ + i;                      System.out.println("I = " +i);                    }                    } (a)  I = 0           (b)  I = 1           (c)  I = 2                (d)  I = 3                (e)  Compile-time Error. Answer : (b) Reason:  1                 The execution goes on like this:                           int i = 0;    //  i becomes 0                           i = 0 + i;  //    now, i becomes 1                           i = 0 + 1;  //    perform addition and assign 1 to i.
3.	Multiple inheritance means, (a)   one class inheriting from more super classes (b)   more classes inheriting from one super class (c)   more classes inheriting from more super classes (d)   None of the above (e)   (a) and (b) above. Answer : (a) Reason:  Multiple inheritance means one class inheriting from more super classes.
4.	Which statement is not true in java language? (a)   A public member of a class can be accessed in all the packages. (b)   A private member of a class cannot be accessed by the methods of the same class. (c)   A private member of a class cannot be accessed from its derived class. (d)   A protected member of a class can be accessed from its derived class. (e)   None of the above. Answer : (b) Reason:  Private members of a class can be accessed by the methods within the same class.
5.	To prevent any method from overriding, we declare the method as, (a)  static        (b)  const            (c)  final              (d)  abstract             (e)  none of the above. Answer : (c) Reason:  Final methods of the base class cannot be overridden in the derived Class.
6.	Which one of the following is not true? (a)   A class containing abstract methods is called an abstract class. (b)   Abstract methods should be implemented in the derived class. (c)   An abstract class cannot have non-abstract methods. (d)   A class must be qualified as ‘abstract’ class, if it contains one abstract method. (e)   None of the above. Answer : (c) Reason:  An abstract class can contain both abstract and non-abstract methods.
7.	The fields in an interface are implicitly specified as, (a)  static only                                        (b)  protected                                        (c)  private (d)  both static and final                         (e)  none of the above. Answer : (d) Reason:  The fields in an interface are implicitly specified as both static and final.
8.	What is the output of the following program:                        public class testmeth                        {                            static int i = 1;                            public static void main(String args[])                             {                                  System.out.println(i+” , “);                                  m(i);                                  System.out.println(i);                             }                             public void m(int i)                             {                                i += 2;                                                           }                        } (a)  1 , 3                  (b)  3 , 1                  (c)  1 , 1                  (d)  1 , 0        (e)  none of the above. Answer : (c) Reason:  Parameter values are passed by value in the calling of a method, and  so a copy of the value is created in the method, and the original value is not affected by the method call.
9.	Which of the following is not true? (a)   An interface can extend another interface. (b)   A class which is implementing an interface must implement all the methods of the interface. (c)   An interface can implement another interface. (d)   An interface is a solution for multiple inheritance in java. (e)   None of the above. Answer : (c) Reason:  An interface can extend another interface but not implement.
10.	Which of the following is true? (a)   A finally block is executed before the catch block but after the try block. (b)   A finally block is executed, only after the catch block is executed. (c)   A finally block is executed whether an exception is thrown or not. (d)   A finally block is executed, only if an exception occurs. (e)   None of the above. Answer : (c) Reason:  A finally block is executed whether an exception is thrown or not is correct. 11. Among these expressions, which is(are) of type String? (a)  "0"                                                   (b)  "ab" + "cd"                                       (c)  '0'  (d)  Both (A) and (B) above                    (e)  (A), (B) and (C) above. Answer : (d) Reason:  Strings are  "0" and "ab" + "cd" . 12. Consider the following code fragment                   Rectangle r1 = new Rectangle();                   r1.setColor(Color.blue);                   Rectangle r2 = r1;                   r2.setColor(Color.red);              After the above piece of code is executed, what are the colors of r1 and                r2 (in this order)?   (a)   Color.blue        Color.red (b)   Color.blue        Color.blue (c)   Color.red        Color.red (d)   Color.red        Color.blue (e)   None of the above. Answer : (c) Reason:  Both r1 and r2 are referring the same object of Rectangle class. So, finally the Color of the object is changed to red. 13. What is the type and value of the following expression? (Notice the integer division)                    -4 + 1/2 + 2*-3 + 5.0 (a)  int -5                                                (b)  double -4.5                                       (c)  int -4                              (d)  double -5.0                                      (e)  None of the above. Answer : (d) Reason:  The execution goes on like this: -4 + 1/2 + 2*-3 + 5.0; -4 +  0 +  -6 +  5.0;  // integer division: 1/2 truncates .5 -10 +  5.0;  // higher type is double 5.0, so -10 is casted to double -5.0;  //  finally, double -5.0. 14. What is printed by the following statement? System.out.print("Hello,\nworld!"); (a)  Hello, \nworld!   (b)  Hello, world!                                    (c)  (d)  "Hello, \nworld!" (e)  None of the above. Answer : (c) Reason:  The statement gives output as System.out.print("Hello,\nworld!"); 15. Consider the two methods (within the same class)          public static int foo(int a, String s)          {            s = "Yellow";            a=a+2;            return a;          }          public static void bar()          {            int a=3;            String s = "Blue";            a = foo(a,s);            System.out.println("a="+a+" s="+s);          }          public static void main(String args[])          {             bar();          } What is printed on execution of these methods? (a)  a = 3 s = Blue                                  (b)  a = 5 s = Yellow                                           (c)  a = 3 s = Yellow (d) a = 5 s = Blue                                   (e) none of the above. Answer : (d) Reason:  ‘a’ value is returned from the method and so it is 5. But the string will remain same, as it is passed by value to the method. 16. Which of the following variable declaration would NOT compile in a java program? (a)  int var;               (b)  int VAR;            (c)  int var1;             (d)  int var_1;           (e)  int 1_var;. Answer : (e) Reason:  The first character of a variable name should not be a digit. 17. Consider the following class definition:             public class MyClass             {             private int value;             public void setValue(int i){ /* code */ }             // Other methods...             } The method setValue assigns the value of i to the instance field value. What could you write for the implementation of setValue? (a)  value = i;                                         (b)  this.value = i;                                (c)  value == i; (d)  Both (A) and (B) and above              (e)  (A), (B) and (C) above. Answer : (d) Reason:  ‘==’ is a comparison operator. 18. Which of the following is TRUE? (a)   In java, an instance field declared public generates a compilation error. (b)   int is the name of a class available in the package java.lang (c)   Instance variable names may only contain letters and digits. (d)   A class has always a constructor (possibly automatically supplied by the java compiler). (e)   The more comments in a program, the faster the program runs. Answer : (d) Reason:  A class will always have a constructor, either provided by the user or a default constructor provided by the compiler. 19. A constructor (a)   Must have the same name as the class it is declared within. (b)   Is used to create objects. (c)   May be declared private (d)   Both (A) and (B) above (e)   (a), (b) and (c) above. Answer : (e) Reason:  A constructor ·                    Must have the same name as the class it is declared within. ·                    Is used to create objects. ·                    May be declared private. 20. Consider,               public class MyClass               {               public MyClass(){/*code*/}                // more code...                } To instantiate MyClass, you would write? (a)   MyClass mc = new MyClass(); (b)   MyClass mc = MyClass(); (c)   MyClass mc = MyClass; (d)   MyClass mc = new MyClass; (e)   The constructor of MyClass should be defined as, public void MyClass(){/*code*/}. Answer : (a) Reason:  An object is created by using a new operator.