User-defined Methods ICSE Class 10 Computer Applications

What User-defined Methods 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

Need, syntax, prototype and signature

Need for methods: (1) reuse code instead of repeating it; (2) break a large problem into small modules (modular programming); (3) make programs easier to read, test and correct; (4) hide details (abstraction).

Syntax:
accessSpecifier modifier returnType methodName(parameter list)
{
body
return value; // if returnType is not void
}
Example:
public static int square(int n)
{
return n * n;
}

Method prototype (header): the first line: public static int square(int n).
Method signature: the method name together with the number, types and order of its parameters: square(int). The return type is not part of the signature.

The return statement sends a value back to the caller and ends the method; a void method returns no value.

Worked example

(2 marks) For the method double interest(double p, double r, int t), write the prototype and the signature.

Try it first, then show the solutionSolution

1. Prototype: double interest(double p, double r, int t) - 1 mark.
2. Signature: interest(double, double, int): name and parameter types only - 1 mark.

Answer: Prototype: double interest(double p, double r, int t). Signature: interest(double, double, int).

Calling methods; actual and formal parameters; static and non-static

A method runs only when it is called (invoked). A non-static (instance) method is called through an object: ob.display(); a static method can be called with the class name or directly from another static method in the same class: Calc.square(4) or square(4).

Formal parameters: the variables in the method header that receive values: int n in square(int n).
Actual parameters (arguments): the values or variables passed in the call: 4 in square(4), or x in square(x).
Actual and formal parameters must match in number, type and order.

If a method returns a value, the call can be used in an expression: int y = square(5) + 1; gives 26.

Worked example

(2 marks) In int sum = add(a, 7); and int add(int x, int y) { return x + y; }, identify the actual and formal parameters.

Try it first, then show the solutionSolution

1. Actual parameters (in the call): a and 7 - 1 mark.
2. Formal parameters (in the header): x and y - 1 mark.

Answer: Actual parameters: a and 7. Formal parameters: x and y.

Call by value and call by reference

Call (pass) by value: a copy of the actual parameter's value is given to the formal parameter. Changes made to the formal parameter inside the method do not affect the original variable. Primitive types (int, double, char, boolean) are always passed by value.

class Demo
{
void change(int x)
{
x = x * 2;
System.out.println("Inside: " + x);
}
public static void main(String args[])
{
Demo d = new Demo();
int a = 5;
d.change(a);
System.out.println("Outside: " + a);
}
}
Output:
Inside: 10
Outside: 5

Call (pass) by reference: the method receives a reference (address) to the actual object, so changes made through it affect the original. In Java this happens when objects or arrays are passed. Example: a method void doubleAll(int arr[]) that runs arr[i] = arr[i] * 2; for every element changes the caller's array {1, 2, 3} to {2, 4, 6}.

Worked example

(1 mark) Invoking a method by passing objects of a class is termed:
(a) call by reference
(b) call by value
(c) call by method
(d) call by constructor

Try it first, then show the solutionSolution

1. Passing an object passes a reference to it.

Answer: (a) call by reference

Pure and impure methods

Pure method (accessor): does not change the state of the object (its member variables) or anything outside it; it usually computes and returns a value from its parameters, and gives the same result for the same arguments. Example: int reverse(int n) that returns the reverse of n; boolean isPrime(int n).

Impure method (mutator / modifier): changes the state of the object, such as modifying member variables (or an array passed to it). Example: void deposit(double amt) { balance = balance + amt; }

Pure methods are easier to test because their output depends only on their input.

Worked example

(1 mark) A method that reverses a given number and returns it, without changing any member variable, is:
(a) impure
(b) pure
(c) a constructor
(d) a destructor

Try it first, then show the solutionSolution

1. It only computes and returns; no state change.

Answer: (b) pure

Method overloading (polymorphism)

Method overloading means defining several methods in the same class with the same name but different parameter lists (different number, types or order of parameters). Java chooses which one to run by matching the arguments in the call. It is compile-time polymorphism.

Valid overloads:
void test(int a, int b) and void test(double a, double b) (types differ)
void test(int a, double b) and void test(double a, int b) (order differs)
void test(int a, double b) and void test(int a) (number differs)

Invalid: void test(int a) and int test(int a): only the return type differs; the signatures are identical, so it is a compile-time error.

In board questions, use exactly the signatures given, take values from the parameters (do not accept them again with Scanner inside), and return a value when the return type is not void.

Worked example

(1 mark) Which pair causes a compile-time error?
(a) void test(int a, int b) and void test(double a, double b)
(b) void test(int a, double b) and void test(double a, int b)
(c) void test(int a, double b) and void test(int a)
(d) void test(int a) and int test(int a)

Try it first, then show the solutionSolution

1. (d) has the same name and the same parameter list; return type alone cannot distinguish them.

Answer: (d) void test(int a) and int test(int a)

User-defined Methods 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

• Calling Methods, Parameters, Call by Value and Pure/Impure Methods
• Method Overloading and Polymorphism

User-defined Methods: syntax and key facts

Method header

accessSpecifier [static] returnType name(type p1, type p2, …)

void if nothing is returned.

Signature

name + number, types and order of parameters (not return type)

Overloads must differ in signature.

Parameter passing

1. 1.Primitives
2. 2.by value (copy); objects/arrays
3. 3.by reference

Programs only for call by value in the syllabus.

Calling

object.method(args) for non-static; ClassName.method(args) or method(args) for static

How the board asks User-defined Methods

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

Tricks to remember User-defined Methods

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

• NTO decides overloading

  Number, Type, Order of parameters can differ; the return type alone cannot.

  Use it when: Valid vs invalid overloads.

• AF: Actual in the cAll, Formal in the header

  Actual values travel in the call; formal names wait in the definition.

  Use it when: Parameter questions.

User-defined Methods: 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 User-defined Methods

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

• ✗Mistake: Not applying overloading or changing method names

  The 2024 and 2025 examiners reported separate programs or renamed methods.

  ✓Do this: Use exactly the method name and signatures given.

  Usually costs: 3 marks or more.

• ✗Mistake: Accepting values inside methods

  The 2024 examiners reported values accepted inside the perform() methods instead of using the arguments.

  ✓Do this: Parameters already carry the values; use them directly.

  Usually costs: 1 to 2 marks per method.

• ✗Mistake: Printing instead of returning

  In 2024 (cone area) and 2025 (series sum) candidates printed values from methods declared to return them.

  ✓Do this: If the return type is not void, end with return value;.

  Usually costs: 1 to 2 marks.

• ✗Mistake: Thinking return type alone overloads a method

  The 2025 MCQ tested this.

  ✓Do this: Signatures must differ in number, type or order of parameters.

  Usually costs: 1 mark.

Practice questions on User-defined Methods

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

   The keyword used when a method returns no value is:
   (a) null
   (b) void
   (c) static
   (d) return

   Hint

   Empty return type.

   Answer

   (b) void

2. Q2 · 1 mark · MCQBoard level

   Parameters in the method definition are called:
   (a) actual parameters
   (b) formal parameters
   (c) arguments
   (d) constants

   Hint

   Header.

   Answer

   (b) formal parameters

3. Q3 · 2 marks · Very short answerBoard level

   Distinguish between pure and impure methods.

   Hint

   State change.

   Answer

   A pure method does not change the state of the object; it returns a value computed from its parameters (e.g. reverse(int n)). An impure method changes the object's state, such as its member variables (e.g. deposit(double amt) changing balance).

4. Q4 · 2 marks · Very short answerHarder board level

   Distinguish between call by value and call by reference.

   Hint

   Copy vs address.

   Answer

   In call by value a copy of the value is passed, so changes inside the method do not affect the original (primitive types). In call by reference a reference to the object is passed, so changes made through it affect the original (objects and arrays).

5. Q5 · 2 marks · Short answerHarder board level

   Give the output:
   static int g(int a)
   {
   a = a + 5;
   return a * 2;
   }
   ...
   int x = 3;
   int y = g(x);
   System.out.println(x + "," + y);

   Hint

   x is copied.

   Answer

   3,16

6. Q6 · 2 marks · Short answerHOTS / competency

   Why is overloading called polymorphism?

   Hint

   Many forms.

   Answer

   Because one method name takes many forms: the same name performs different tasks depending on the arguments, which is the meaning of polymorphism (many forms).

7. Q7 · 15 marks · Long answerHarder board level

   Define a class to overload the method series: void series(int n) prints the first n square numbers (1 4 9 ...); double series(double x, int n) returns x + x² + ... + xⁿ. Write main() to call series(5) and print series(2.0, 4).

   Hint

   Math.pow for powers.

   Answer

   class Series
   {
   void series(int n)
   {
   for (int i = 1; i <= n; i++)
   System.out.print(i * i + " ");
   System.out.println();
   }
   double series(double x, int n)
   {
   double s = 0;
   for (int i = 1; i <= n; i++)
   s = s + Math.pow(x, i);
   return s;
   }
   public static void main(String args[])
   {
   Series ob = new Series();
   ob.series(5);
   System.out.println(ob.series(2.0, 4));
   }
   }
   Output:
   1 4 9 16 25
   30.0 (2 + 4 + 8 + 16)

8. Q8 · 2 marks · Very short answerBoard level

   Write a method int countDigits(long n) that returns the number of digits, and state whether it is pure.

   Hint

   Divide by 10.

   Answer

   int countDigits(long n)
   {
   int c = 0;
   do
   {
   c++;
   n = n / 10;
   } while (n > 0);
   return c;
   }
   It is pure: it changes only its own copy of n and returns a value. (do-while makes 0 count as 1 digit.)

9. Q9 · 2 marks · Short answerHOTS / competency

   Suppose a class has void show(int a, double b) and void show(double a, int b). Which runs for show(4, 5)? Explain.

   Hint

   Ambiguity.

   Answer

   Neither can be chosen: both need one int widened to double, so the call is ambiguous and the compiler reports an error. A call such as show(4, 5.0) would choose show(int, double).

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.Is the return type part of the signature?Show answer

   No.

2. 2.How are primitives passed in Java?Show answer

   By value.

3. 3.A method that changes member variables is?Show answer

   Impure.

4. 4.Same name, different parameter lists is called?Show answer

   Method overloading.

5. 5.Which statement sends a value back?Show answer

   return

Quick revision checklist

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

• ☐Method = named block for one task; reuse and modularity.
• ☐Prototype = header; signature = name + parameter types.
• ☐Actual in call, formal in header; match number, type, order.
• ☐Primitives by value; objects/arrays by reference.
• ☐Pure: no state change; impure: changes state.
• ☐Overloading: same name, different parameters; return type alone is not enough.

User-defined Methods: frequently asked questions