Anatomy of a Class Practice

Sample questions

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1. Sample 1difficulty 1/5

   public class Account {
       private double balance;
       public double getBalance() { return balance; }
       public void deposit(double amt) {
           if (amt > 0) balance += amt;
       }
   }
   // ...

   Which best describes why balance is private?

   • A

     To enforce encapsulation; outside code must use methods that validate access and modification

     check_circle
   • B

     Because private variables run faster

   • C

     So they cannot be initialized

   • D

     So static methods cannot use them

   Why

   Encapsulation hides internal state and exposes a controlled interface, allowing validation logic in the methods.

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2. Sample 2difficulty 2/5

   public class Box {
       private final int CAPACITY;
       public Box(int c) { CAPACITY = c; }
       public int getCap() { return CAPACITY; }
   }
   // ...
   Box b = new Box(50);
   System.out.println(b.getCap());

   What is printed?

   • A

     50

     check_circle
   • B

     Compile-time error: cannot assign final

   • C

     0

   • D

     null

   Why

   A blank final instance variable can be assigned exactly once in the constructor; this is allowed.

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3. Sample 3difficulty 2/5

   Which is the correct minimal class declaration?

   • A

     Dog class { }

   • B

     public Dog { }

   • C

     class Dog { }

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   • D

     class { Dog }

   Why

   <code>class ClassName { }</code> defines an empty class. <code>public</code> is optional but common.

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4. Sample 4difficulty 2/5

   An instance variable is declared

   • A

     Inside the class body, outside methods

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   • B

     Inside a method

   • C

     Outside the class file

   • D

     As a parameter

   Why

   Instance fields belong to each object; declared at class level.

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5. Sample 5difficulty 3/5

   <code>Dog a = new Dog(); Dog b = new Dog();</code> — a and b are

   • A

     Compile error

   • B

     References to null

   • C

     Two distinct objects with their own state

     check_circle
   • D

     The same object

   Why

   Each <code>new</code> creates a fresh object.

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