User-Defined Methods

ICSE Class 10 · Computer Applications · Chapter 3

What this chapter covers

Need for methods
Syntax of a method, method prototype and signature
Forms of methods: ways to define a method
Method definition and method calling
Returning values from methods
Static and non-static methods
Object creation and modular programming with multiple methods
Call by value (pass by value)
Call by reference (pass by reference)
Pure and impure methods
Method overloading (polymorphism)

Key points

A user-defined method is a named block of statements, written by the programmer, that performs one task and is called when needed.
Methods give reusability, less repetition, easier debugging and modular programming.
A method header contains an optional access specifier and modifier, a compulsory return type, the method name and the parameter list.
The prototype is the complete first line of a method; the signature is only the name with the number, types and order of parameters.
Methods take four forms, depending on whether they receive parameters and whether they return a value.
Actual parameters appear in the call; formal parameters appear in the header and receive copies of the actual values, matched by position and type.
`return` ends a method and sends back exactly one value of the declared type; a `void` method returns nothing and is called as a statement.
Static methods belong to the class and need no object; non-static methods belong to objects and are called as `object.method()`.
Data members store an object's state; member methods work on them; `new` creates the object through which member methods are invoked.
Call by value passes a copy, so the caller's variable is unchanged; Java passes every primitive type this way.
Call by reference passes the reference, so changes inside the method are seen by the caller; in Java this happens with objects and arrays.
A pure method does not change the state of an object; an impure method changes it.
Method overloading means several methods with the same name but different parameter lists; it is compile-time polymorphism, and a different return type alone does not make an overload.

Questions answered

Define a user-defined method and give two reasons for using methods in a program.

A user-defined method is a named block of statements, written by the programmer inside a class, that performs one specific task and can be called when needed. Methods allow code to be reused without repetition, and they make a program modular, so errors are easier to find and correct.

Distinguish between a method prototype and a method signature, using `public static int sum(int a, int b)` as the example.

The prototype is the whole first line, `public static int sum(int a, int b)`, including the access specifier, modifier and return type. The signature is only the name with the parameter types, `sum(int, int)`.

Write the prototype of a method `isPalindrome` that accepts an integer and returns `true` or `false`.

`boolean isPalindrome(int n)`

Identify the actual and formal parameters in: `double avg(int x, int y) { return (x + y) / 2.0; }` called as `double r = avg(m1, m2);`.

`m1` and `m2` are the actual parameters; `x` and `y` are the formal parameters.

What is the value returned by `avg(7, 8)` in Question 4, and why is `2.0` used instead of `2`?

(7 + 8) / 2.0 = 7.5. Dividing by `2.0` makes the division a `double` division; dividing by `2` would do integer division and give 7, which would then be stored as 7.0.

Why does the statement `int x = display();` give an error if `display()` is declared as `void display()`?

A `void` method returns no value, so there is nothing to assign to `x`. A `void` method must be called as a statement on its own.

Give the output, and state which way of passing is used. `static void inc(int n) { n++; }` with `int a = 5; inc(a); System.out.println(a);`

The output is `5`. The value of `a` is passed by value, so only the copy `n` becomes 6.

Why can `main()` call `Math.sqrt()` without creating an object, but not a non-static method of its own class?

`Math.sqrt()` is static, so it belongs to the class and is called with the class name. A non-static method belongs to an object; `main()` is static and has no object, so it must create one and call the method through it.

Past board exam questions

ICSE 2026 board paper · 15 marks

Define a class to overload the method format as follows: void format (): To print the following pattern using Nested for loops only: 1 2 3 4 5 2 3 4 5 3 4 5 4 5 5 int format (String s): To calculate and return the sum of ASCII codes of each character of the String. Example: CAB Output: 67 + 65 + 66 198 void format (int n): To calculate and display the sum of natural numbers up to n given by the formula. (n(n+1))/(2)

Show answer

``` class Overload { void format() { for (int i = 1; i <= 5; i++) { for (int j = i; j <= 5; j++) System.out.print(j + " "); System.out.println(); } } int format(String s) { int sum = 0; for (int i = 0; i < s.length(); i++) sum += (int) s.charAt(i); return sum; } void format(int n) { int sum = n * (n + 1) / 2; System.out.println("Sum of natural numbers up to " + n + " = " + sum); } public static void main(String args[]) { Overload ob = new Overload(); ob.format(); System.out.println(ob.format("CAB")); …

ICSE 2026 board paper · 1 mark

In the following method prototype to accept a character, an integer and return YES or NO, fill in the blank to complete the method prototype. public ________ someMethod (char ch, int n)

boolean
String
int
double

Show answer

String

ICSE 2026 board paper · 1 mark

In a calculator which Java feature allows multiple methods named calculate() for the different operations?

abstraction
inheritance
encapsulation
polymorphism

Show answer

polymorphism

ICSE 2025 compartment paper · 15 marks

Define a class to overload the method transform as follows: int transform(int n) – to return the sum of the digits of the given number Example: n = 458 output : 17 void transform(String s) – to convert the given String to upper case and print Example: if S = "Blue" Output : BLUE void transform (char ch) – to print the character ch in 3 rows and 3 columns using nested loops. Example: if ch = '@' Output : @@@ @@@ @@@

Show answer

class Overload { int transform(int n) { int sum = 0; n = Math.abs(n); while (n > 0) { sum = sum + n % 10; // add last digit n = n / 10; } return sum; } void transform(String s) { System.out.println(s.toUpperCase()); } void transform(char ch) { for (int i = 1; i <= 3; i++) { for (int j = 1; j <= 3; j++) System.out.print(ch); System.out.println(); } } public static void main(String args[]) { Overload ob = new Overload(); System.out.println(ob.transform(458)); // 17 …

ICSE 2025 board paper · 15 marks

Define a class to overload the method print( ) as follows: void print ( ) – To print the given format using nested loops. ``` @#@#@ @#@#@ @#@#@ @#@#@ ``` double print(double a, double b) – To display the sum of numbers between a and b with difference of 0.5. e.g. if a = 1.0, b = 4.0 output is: 1.0 + 1.5 + 2.0 + 2.5 + ……………. + 4.0 int print(char ch1, char ch2) – compare the two characters and return the ASCII code of the largest character.

Show answer

class Overload { void print() { for (int i = 1; i <= 4; i++) // 4 rows { for (int j = 1; j <= 5; j++) // 5 symbols in each row { if (j % 2 == 1) System.out.print("@"); else System.out.print("#"); } System.out.println(); } } double print(double a, double b) { double sum = 0; for (double x = a; x <= b; x += 0.5) sum += x; System.out.println("Sum = " + sum); return sum; } int print(char ch1, char ch2) { if (ch1 > ch2) return (int) ch1; …

ICSE 2025 sample paper · 15 marks

Define a class to overload the method display() as follows: void display(): To print the following format using nested loop. ``` 1 2 1 2 1 1 2 1 2 1 1 2 1 2 1 ``` void display (int n, int m) : To print the quotient of the division of m and n if m is greater than n otherwise print the sum of twice n and thrice m. double display (double a, double b, double c) – to print the value of z where z = p × q p = (a+b)/(c) q = a + b + c

Show answer

```java class Overload { void display() { for (int i = 1; i <= 3; i++) { for (int j = 1; j <= 5; j++) { if (j % 2 == 1) System.out.print("1 "); else System.out.print("2 "); } System.out.println(); } } void display(int n, int m) { if (m > n) System.out.println("Quotient = " + (m / n)); else System.out.println("Sum = " + (2 * n + 3 * m)); } double display(double a, double b, double c) { double p = (a + b) / c; double q = a + b + c; double z = p * q; …

ICSE 2025 compartment paper · 1 mark

Which statement is correct for the method prototype given below: int check(char ch, String s)

check( ) does not return any value
check( ) has return type int
check method has two actual parameters
check( ) is a constructor

Show answer

check( ) has return type int

ICSE 2025 compartment paper · 1 mark

The statement given below is termed as: pubic void Accept(int a)

Method signature
Method block
Method prototype
Constructor

Show answer

Method prototype