Encapsulation ICSE Class 10 Computer Applications

What Encapsulation is about

Weightage: CISCE publishes no chapter weightage. Section A (40 marks) is compulsory: 1-mark MCQs and 2-mark short answers including output and error questions; in Section B you answer any four of six 15-mark programming questions written in Java.Source: CISCE ICSE Computer Applications (661) specimen paper structure for 2027

Key concepts

Meaning and benefits of encapsulation

Encapsulation is the binding of data (variables) and the methods that act on it into a single unit, the class, together with restricting direct access to the data from outside. Usually the data is made private and public methods are provided to read it (getters/accessors) or change it (setters/mutators), which can check the values first (data hiding).

Benefits: (1) data security: outside code cannot set invalid values; (2) control: changes happen only through checked methods; (3) easier maintenance: internal details can change without affecting other code; (4) modularity and reuse.

Real-life example: a medicine capsule; a bank where you cannot touch the vault but can deposit and withdraw through the counter.

Worked example

(2 marks) Define encapsulation and give one benefit.

Try it first, then show the solutionSolution

1. Binding data and methods into one class and restricting direct access to the data - 1 mark.
2. Benefit: data security, since data can change only through the class's own checked methods - 1 mark.

Answer: Encapsulation is wrapping data and the methods that operate on it into a single class while restricting direct access to the data. Benefit: the data is protected, because it can be changed only through the class's own methods, which can reject invalid values.

Access specifiers and visibility rules

Access specifiers decide where a class member can be used.

private: accessible only inside the same class. Most restrictive (least accessible).
default (no specifier, 'package' access): accessible to any class in the same package.
protected: accessible in the same package and in subclasses (even in other packages).
public: accessible from everywhere. Least restrictive.

Visibility table (accessible = yes):

Specifier	Same class	Same package	Subclass in another package	Any other class
private	yes	no	no	no
default	yes	yes	no	no
protected	yes	yes	yes	no
public	yes	yes	yes	yes

Order from least to most accessible: private < default < protected < public.

Worked example

(1 mark) The access specifier that gives the least accessibility is:
(a) package
(b) public
(c) protected
(d) private

Try it first, then show the solutionSolution

1. private allows access only within the class itself.

Answer: (d) private

Getters and setters

A common encapsulation pattern:
class Student
{
private int marks;
public void setMarks(int m)
{
if (m >= 0 && m <= 100)
marks = m;
else
System.out.println("Invalid marks");
}
public int getMarks()
{
return marks;
}
}

Another class cannot write s.marks = 150; (marks is private: compile-time error). It must call s.setMarks(150), which rejects the value. getMarks() lets others read the value safely. setMarks is an impure (mutator) method; getMarks is a pure (accessor) method.

Worked example

(2 marks) Another class has Student s = new Student(); and writes s.marks = 95;. Why is this an error, and how should it be done?

Try it first, then show the solutionSolution

1. marks is private, so it is not visible outside Student: compile-time error - 1 mark.
2. Use the public setter: s.setMarks(95); - 1 mark.

Answer: Because marks is private, it cannot be accessed outside the Student class, so the compiler reports an error. Use the public method: s.setMarks(95);.

Scope of variables

Scope is the part of a program in which a variable can be used.

Class (static) variables: declared with static in the class; one copy shared by all objects; exist as long as the class is loaded; usable throughout the class (and outside, depending on access).
Instance variables: declared in the class without static; one copy per object; exist as long as the object exists; usable in all non-static methods of the class.
Argument (parameter) variables: declared in a method's header; exist only while that method runs; usable only inside that method.
Local variables: declared inside a method or a block; usable only from the point of declaration to the end of that block; they have no default value and must be assigned before use. A variable declared in a for header (for (int i = ...)) is local to the loop.

If a local or argument variable has the same name as a member variable, inside that method the local one hides (shadows) the member.

Worked example

(2 marks) Identify the class, instance, argument and local variables:
class Shop
{
static int count;
double sales;
void sell(double amt)
{
double tax = amt * 0.05;
sales += amt + tax;
count++;
}
}

Try it first, then show the solutionSolution

1. Class variable: count (static). Instance variable: sales - 1 mark.
2. Argument variable: amt. Local variable: tax - 1 mark.

Answer: Class variable: count. Instance variable: sales. Argument variable: amt. Local variable: tax.

Scope in action

class Scope
{
int x = 10; // instance variable
void show(int x) // argument x hides the member x
{
int y = x * 2; // local variable
System.out.println(x + " " + y);
}
void showMember()
{
System.out.println(x);
}
public static void main(String args[])
{
Scope s = new Scope();
s.show(3);
s.showMember();
}
}
Output:
3 6
10

In show(), x means the argument (3); in showMember(), x means the instance variable (10). y cannot be used outside show().

Worked example

(2 marks) Why is this an error? for (int i = 1; i <= 5; i++) { } System.out.println(i);

Try it first, then show the solutionSolution

1. i is declared in the for header, so its scope is the loop only - 1 mark.
2. After the loop i does not exist: compile-time error; declare int i; before the loop to use it later - 1 mark.

Answer: i is local to the for loop, so it cannot be used after the loop (cannot find symbol). Declare it before the loop: int i; for (i = 1; i <= 5; i++) { } System.out.println(i); which prints 6.

Encapsulation in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Access Specifiers and Variable Scope Programs

Encapsulation: syntax and key facts

Visibility order

private < default (package) < protected < public

private = least accessible.

Encapsulation pattern

private data + public getX() / setX(value with checks)

Data hiding.

Scope

class (static) > instance (per object) > argument (method call) > local (block)

Local variables have no default value.

How the board asks Encapsulation

The question patterns to expect, and the method that works for each.

Tricks to remember Encapsulation

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Pri-De-Pro-Pub

  Private, Default, Protected, Public: from the tightest lock to the open door.

  Use it when: Order of accessibility.

• CIAL scope

  Class, Instance, Argument, Local: from the longest life to the shortest.

  Use it when: Types of variables by scope.

Encapsulation: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section B style)

Read the situation, then answer every part. In the board paper this is a 10-mark question split into 2 + 3 + 5 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Encapsulation

The slips examiners see most often, and what to write instead.

• ✗Mistake: Choosing public as least accessible

  The 2024 examiners noted candidates answered public, apparently because they used only public in programs.

  ✓Do this: private is the least accessible; public the most.

  Usually costs: 1 mark.

• ✗Mistake: Choosing protected for open-to-all examples

  In 2025 candidates chose protected for the post office.

  ✓Do this: Open to everyone = public.

  Usually costs: 1 mark.

• ✗Mistake: Using a local variable outside its block

  Loop variables declared in for headers are often printed after the loop.

  ✓Do this: Declare the variable before the loop if it is needed afterwards.

  Usually costs: 1 mark.

• ✗Mistake: Accessing private members from another class

  Students write ob.balance when balance is private.

  ✓Do this: Use public getter or setter methods.

  Usually costs: 1 to 2 marks.

Practice questions on Encapsulation

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   Which specifier makes a member accessible to all classes?
   (a) private
   (b) protected
   (c) public
   (d) default

   Hint

   Open.

   Answer

   (c) public

2. Q2 · 1 mark · MCQBoard level

   A variable declared inside a method is a:
   (a) class variable
   (b) instance variable
   (c) local variable
   (d) static variable

   Hint

   Inside.

   Answer

   (c) local variable

3. Q3 · 1 mark · MCQHarder board level

   A member with no access specifier can be accessed by:
   (a) every class
   (b) classes in the same package
   (c) only its own class
   (d) only subclasses

   Hint

   Package access.

   Answer

   (b) classes in the same package

4. Q4 · 2 marks · Very short answerBoard level

   Distinguish between private and public access.

   Hint

   Where visible.

   Answer

   A private member is accessible only within its own class; a public member is accessible from any class anywhere.

5. Q5 · 2 marks · Very short answerHarder board level

   Distinguish between an instance variable and a local variable on two points.

   Hint

   Where declared; default value.

   Answer

   (1) An instance variable is declared in the class outside methods and lasts as long as the object; a local variable is declared inside a method or block and lasts only while it runs. (2) Instance variables get default values (0, null); local variables must be assigned before use.

6. Q6 · 2 marks · Short answerHOTS / competency

   Why are data members usually private and methods public?

   Hint

   Control.

   Answer

   Private data cannot be changed directly from outside, so the class keeps control and can validate every change; public methods provide the controlled ways for other classes to use the object.

7. Q7 · 15 marks · Long answerBoard level

   Define a class Rectangle with private length and breadth, a public method set(double l, double b) that accepts only positive values, and public methods area() and perimeter(). Write main() to set 6 and 4 and print both.

   Hint

   Validate in set().

   Answer

   class Rectangle
   {
   private double length, breadth;
   public void set(double l, double b)
   {
   if (l > 0 && b > 0)
   {
   length = l;
   breadth = b;
   }
   else
   System.out.println("Invalid sides");
   }
   public double area() { return length * breadth; }
   public double perimeter() { return 2 * (length + breadth); }
   public static void main(String args[])
   {
   Rectangle r = new Rectangle();
   r.set(6, 4);
   System.out.println("Area = " + r.area());
   System.out.println("Perimeter = " + r.perimeter());
   }
   }
   Output:
   Area = 24.0
   Perimeter = 20.0

8. Q8 · 2 marks · Short answerHOTS / competency

   Give the output:
   class Q
   {
   int n = 5;
   void m()
   {
   int n = 8;
   n++;
   System.out.print(n + " ");
   }
   public static void main(String args[])
   {
   Q q = new Q();
   q.m();
   System.out.println(q.n);
   }
   }

   Hint

   Local hides member.

   Answer

   9 5 (the local n becomes 9; the instance n stays 5)

9. Q9 · 2 marks · Very short answerBoard level

   State the scope of an argument variable.

   Hint

   Method.

   Answer

   An argument (parameter) variable can be used only inside the method in whose header it is declared, and exists only while that method is running.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Most restrictive specifier?Show answer

   private

2. 2.Which specifier allows subclasses in other packages?Show answer

   protected (and public)

3. 3.Do local variables get default values?Show answer

   No.

4. 4.Scope of a variable declared in a for header?Show answer

   The loop only.

5. 5.What is data hiding?Show answer

   Keeping data private and allowing access only through methods.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Encapsulation: data + methods in a class; data hidden.
• ☐private (class) < default (package) < protected (package + subclasses) < public (all).
• ☐Getters read, setters change with checks.
• ☐Class (static), instance, argument, local variables.
• ☐Local variables: no default value; scope ends with the block.

Encapsulation: frequently asked questions