Why encapsulation is required in Java - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a private variable in a class.

Java

public class Person {
    private String [1];
}

Drag options to blanks, or click blank then click option'

APerson

BgetName

Cname

Dpublic

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names or access modifiers instead of variable names.

The variable name is declared private to hide it from outside access, which is a key part of encapsulation.

2fill in blank

medium

Complete the code to create a public getter method for the private variable.

Java

public String [1]() {
    return name;
}

Drag options to blanks, or click blank then click option'

AsetName

Bname

CName

DgetName

Attempts:

3 left

💡 Hint

Common Mistakes

Using setter method names or variable names instead of getter method names.

The getter method is named getName to provide controlled access to the private variable name.

3fill in blank

hard

Fix the error in the setter method to properly set the private variable.

Java

public void setName(String [1]) {
    this.name = [1];
}

Drag options to blanks, or click blank then click option'

AsetName

Bname

CName

Dthis

Attempts:

3 left

💡 Hint

Common Mistakes

Using different parameter names or keywords incorrectly.

The parameter name should match the variable name to correctly assign the value using this.name = name;.

4fill in blank

hard

Fill both blanks to complete the encapsulated class with private variable and public getter.

Java

public class [1] {
    private int [2];

    public int getAge() {
        return age;
    }
}

Drag options to blanks, or click blank then click option'

AStudent

Bage

Cscore

DPerson

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names that do not match getter methods.

The class is named Student and the private variable is age to demonstrate encapsulation.

5fill in blank

hard

Fill all three blanks to complete the class with private variable, getter, and setter methods.

Java

public class [1] {
    private String [2];

    public String getName() {
        return [2];
    }

    public void setName(String [3]) {
        this.name = [3];
    }
}

Drag options to blanks, or click blank then click option'

AEmployee

Bname

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for setter parameter and private variable.

The class is Employee, the private variable is name, and the setter parameter is also name to properly encapsulate the data.

Practice

1. Why is encapsulation important in Java programming?

easy

A. It allows multiple inheritance.

B. It makes the program run faster.

C. It protects data by hiding it from outside access.

D. It automatically fixes errors in code.

Solution

1. Step 1: Understand encapsulation purpose

   Encapsulation hides the internal state of an object to protect it from unauthorized access.

2. Step 2: Identify the correct benefit

   Protecting data by hiding it is the main reason for encapsulation, not speed or inheritance.

3. Final Answer:

   It protects data by hiding it from outside access. -> Option C

4. Quick Check:

   Encapsulation = Data protection [OK]

Hint: Encapsulation hides data to keep it safe [OK]

Common Mistakes:

• Thinking encapsulation improves speed
• Confusing encapsulation with inheritance
• Believing it fixes code errors automatically

2. Which of the following is the correct way to declare a private variable in Java?

easy

A. private int age;

B. public int age;

C. protected int age;

D. int private age;

Solution

1. Step 1: Recall Java access modifiers

   Private variables are declared using the keyword 'private' before the type and name.

2. Step 2: Check each option

   Only 'private int age;' uses correct syntax for a private variable.

3. Final Answer:

   private int age; -> Option A

4. Quick Check:

   Private variable syntax = private int variableName [OK]

Hint: Private variables start with 'private' keyword [OK]

Common Mistakes:

• Placing 'private' after the type
• Using 'int private' which is invalid syntax
• Confusing 'public' or 'protected' with 'private'

3. What will be the output of this Java code?

class Person {
  private String name = "Alice";
  public String getName() {
    return name;
  }
}
public class Test {
  public static void main(String[] args) {
    Person p = new Person();
    System.out.println(p.getName());
  }
}

medium

A. Compilation error

B. Alice

C. null

D. Runtime error

Solution

1. Step 1: Understand encapsulation usage in code

   The private variable 'name' is accessed via the public method getName(), which returns "Alice".

2. Step 2: Predict output of System.out.println

   Calling p.getName() prints the value "Alice" stored in the private variable.

3. Final Answer:

   Alice -> Option B

4. Quick Check:

   Getter method returns private data = Alice [OK]

Hint: Getter methods return private data safely [OK]

Common Mistakes:

• Expecting direct access to private variable
• Thinking code causes compilation error
• Assuming null because variable is private

4. Identify the error in this Java class related to encapsulation:

public class Car {
  public String model;
  private int speed;
  public void setSpeed(int speed) {
    speed = speed;
  }
}

medium

A. The variable 'model' should be private.

B. The method setSpeed should be private.

C. The class should not have any private variables.

D. The setter method does not update the private variable correctly.

Solution

1. Step 1: Analyze setter method code

   The line 'speed = speed;' assigns the parameter to itself, not to the class variable.

2. Step 2: Identify correct assignment

   To update the private variable, use 'this.speed = speed;' to refer to the class field.

3. Final Answer:

   The setter method does not update the private variable correctly. -> Option D

4. Quick Check:

   Setter must assign to 'this.variable' [OK]

Hint: Use 'this.' to assign to class variables in setters [OK]

Common Mistakes:

• Assigning parameter to itself inside setter
• Not using 'this' keyword for class fields
• Making variables public when they should be private

5. How does encapsulation help in controlling access to sensitive data in a banking application?

hard

A. By hiding data using private variables and providing controlled access via methods.

B. By removing all methods and only using variables.

C. By allowing direct modification of data from anywhere.

D. By making all variables public for easy access.

Solution

1. Step 1: Understand encapsulation in real-world context

   In banking apps, sensitive data must be hidden to prevent unauthorized changes.

2. Step 2: Identify how encapsulation controls access

   Private variables hide data; public methods allow controlled reading or updating with checks.

3. Final Answer:

   By hiding data using private variables and providing controlled access via methods. -> Option A

4. Quick Check:

   Encapsulation = Hide data + controlled access [OK]

Hint: Private variables + public methods control sensitive data [OK]

Common Mistakes:

• Making variables public for convenience
• Allowing direct data modification everywhere
• Ignoring the need for controlled access