Java Methods, Overloading and Constructors (ISC Class 11 Computer Science)

Understand Methods: Arguments, Call by Value, Overloading, and Constructors

static int sq(int x) { return x * x; }       // x is a formal parameter
int r = sq(5);                                // 5 is the actual argument; r = 25

static void change(int x) { x = x + 10; }
int a = 5; change(a);            // a is still 5
static void chg(int[] p) { p[0] = 99; }
int[] q = {1, 2}; chg(q);        // q[0] is now 99 (the array object is shared)

int add(int a, int b) { return a + b; }
double add(double a, double b) { return a + b; }

class Box { int l, b;
    Box() { l = 1; b = 1; }
    Box(int x) { l = x; b = x; }
    Box(int x, int y) { l = x; b = y; }
    int area() { return l * b; } }

Methods: Arguments, Call by Value, Overloading, and Constructors: key facts

Method header

accessSpecifier returnType name(type param, ...) | void means no return value

Syntax.

Overloading rule

• •Same name
• •Different number or types of parameters
• •Return type alone is not enough

Compile-time choice.

Constructor rules

• •Same name as class
• •No return type
• •Called by new
• •Compiler supplies default only if none is written

Key points.

How to answer Methods: Arguments, Call by Value, Overloading, and Constructors questions

1. 1Write the formal parameters and the actual arguments side by side.
2. 2For primitives, copy the value; for arrays and objects, track the shared object.
3. 3For overloading, pick the method with the exact or nearest parameter types.
4. 4For constructors, check which one is chosen by the number of arguments.

Methods: Arguments, Call by Value, Overloading, and Constructors in real life

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

Tricks to remember Methods: Arguments, Call by Value, Overloading, and Constructors

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

• Formal in header, actual in call

  Formal = declared; actual = supplied.

  Use it when: Arguments.

• Overload = same name, different list

  Not by return type.

  Use it when: Overloading.

• Constructor has no return type

  Not even void.

  Use it when: Constructors.

Methods: Arguments, Call by Value, Overloading, and Constructors: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

static void change(int x) { x = x + 10; }
static void chg(int[] p) { p[0] = 99; }
// in main
int a = 5; change(a);
int[] q = {1, 2}; chg(q);
System.out.println(a + " " + q[0] + " " + q[1]);

Where students lose marks in Methods: Arguments, Call by Value, Overloading, and Constructors

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

• ✗Mistake: Giving the constructor a return type

  Writing it like a method.

  Wrong working

  void Box() { }

  Right working

  Box() { }

  ✓Do this: No return type.

  Usually costs: 1-2 marks.

• ✗Mistake: Assuming primitives change in the caller

  Confusing with arrays.

  Wrong working

  a becomes 15

  Right working

  a stays 5

  ✓Do this: Call by value.

  Usually costs: 2 marks.

• ✗Mistake: Overloading by return type only

  Misconception.

  Wrong working

  int f(int a) and double f(int a)

  Right working

  Parameters must differ

  ✓Do this: Change the parameter list.

  Usually costs: 1-2 marks.

Practice questions on Methods: Arguments, Call by Value, Overloading, and Constructors

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

   Method overloading is also called:
   (a) run-time polymorphism (b) compile-time (static) polymorphism (c) inheritance (d) abstraction

   Hint

   Decided by the compiler.

   Answer

   (b) compile-time (static) polymorphism

2. Q2 · 3 marks · Short answerBoard level

   Differentiate between a method and a constructor on any three points. (3 marks)

   Hint

   Name, return type, call.

   Answer

   A constructor has the class name, a method has any name; a constructor has no return type, a method has a return type or void; a constructor is called automatically by new, a method is called explicitly.

3. Q3 · 3 marks · Short answerHarder board level

   Write the output: static int f(int n) { n = n * 2; return n + 1; } int x = 4; int y = f(x); System.out.println(x + " " + y + " " + f(f(2))); (3 marks)

   Hint

   f(2) = 5, f(5) = 11.

   Answer

   x remains 4; f(4) = 9; f(f(2)): f(2) = 5 then f(5) = 11. Output: 4 9 11

4. Q4 · 5 marks · Long answerHarder board level

   Define a class Student with a default constructor (name "NA", marks 0) and a parameterised constructor, and a method that returns the grade "P" for marks of 40 or more else "F". Give the output for new Student() and new Student("Ravi", 62). (5 marks)

   Hint

   Two objects.

   Answer

   class Student { String name; int marks; Student() { name = "NA"; marks = 0; } Student(String n, int m) { name = n; marks = m; } String grade() { return marks >= 40 ? "P" : "F"; } } new Student().grade() gives F; new Student("Ravi", 62).grade() gives P.

5. Q5 · 3 marks · Short answerHOTS / competency

   A class has constructors Box(int a) and Box(double a). A call new Box(5) and a call new Box(5.0f) are made. Say which constructor each calls and why, and what happens for new Box(5L). (3 marks)

   Hint

   Widening.

   Answer

   new Box(5) calls Box(int a) (exact match). new Box(5.0f) widens float to double and calls Box(double a). new Box(5L) widens long to double (long cannot go to int), so Box(double a) is called.

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.Constructor name?Show answer

   Same as the class.

2. 2.Primitive arguments are passed by?Show answer

   Value.

3. 3.Overloading differs by?Show answer

   Parameter list.

4. 4.Default constructor supplied when?Show answer

   No constructor is written.

5. 5.Void means?Show answer

   Returns nothing.

Methods: Arguments, Call by Value, Overloading, and Constructors: frequently asked questions