Creating and Storing Objects (Instantiation) Practice

Sample questions

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1. Sample 1difficulty 2/5

   Which line creates a new <code>Scanner</code> object reading from System.in?

   • A

     Scanner s = Scanner.in;

   • B

     Scanner s = new Scanner();

   • C

     Scanner s = new Scanner(System.in);

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   • D

     Scanner s = System.scanner;

   Why

   Constructor takes the input stream; <code>new</code> allocates the object.

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2. Sample 2difficulty 3/5

   public class Cell {
       public int v;
   }
   public class Helper {
       public static void replace(Cell c) {
           c = new Cell();
           c.v = 999;
       }
   }
   // ...
   Cell c = new Cell();
   c.v = 10;
   Helper.replace(c);
   System.out.println(c.v);

   What is printed?

   • A

     999

   • B

     10

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   • C

     Compile-time error

   • D

     0

   Why

   Reassigning the parameter c inside replace only changes the local variable; the original reference is unchanged.

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3. Sample 3difficulty 3/5

   The keyword <code>new</code> is used to

   • A

     Allocate a new object and call its constructor

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   • B

     Declare a variable

   • C

     Compare references

   • D

     Cast a type

   Why

   <code>new ClassName(...)</code> allocates memory and runs constructor.

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4. Sample 4difficulty 4/5

   When passing an object reference to a method, Java passes

   • A

     The reference by value (the method has its own reference variable to the same object)

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   • B

     By reference (caller's variable can be reassigned)

   • C

     The whole object by value

   • D

     Deep copy

   Why

   Java is always pass-by-value; for objects, it's the reference value that's copied — both refer to the same object, but reassigning inside the method doesn't affect the caller.

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5. Sample 5difficulty 4/5

   After <code>Box a = new Box(); Box b = a;</code>, modifying <code>b</code> (through its methods)

   • A

     Modifies the same object that a refers to

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   • B

     Has no effect on a

   • C

     Throws an error

   • D

     Creates a copy

   Why

   <code>b = a;</code> copies the reference, not the object. Both refer to the same Box.

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