Method Overloading and Polymorphism in Java (ICSE Class 10)

Understand Method Overloading and Polymorphism

Method Overloading and Polymorphism: key facts

What differs in an overload

• •Number of parameters
• •Types of parameters
• •Order of parameter types
• •Not the return type alone
• •Not parameter names

Any one difference is enough.

Matching a call

• •Exact match first
• •Then widening: byte, short, int, long, float, double
• •char widens to int
• •No match or tie: compile-time error

long goes to float or double, never to int.

Polymorphism link

Method overloading = compile-time polymorphism | One name, many forms

The syllabus treats it as polymorphism in Class X.

Invalid overload

• •Same name
• •Same parameter types in the same order
• •Different return type only

Compiler error: method already defined.

How to answer Method Overloading and Polymorphism questions

1. 1List every version with its parameter types.
2. 2Write the type of each argument in the call.
3. 3Pick the version whose parameter types match exactly.
4. 4If none matches exactly, widen each argument (int to long, float, double) and choose the nearest.
5. 5If two versions fit equally, say the call is ambiguous (a compile-time error).

Method Overloading and Polymorphism 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 Method Overloading and Polymorphism

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

• N-T-O

  Overloads differ in Number, Type or Order of the parameters, never only in return type.

  Use it when: Validity checks.

• Smaller to bigger

  Arguments climb up to the next bigger type if there is no exact match, never down.

  Use it when: Which method is called.

• Compiler chooses

  Overloading is decided by the compiler from the arguments in the call.

  Use it when: Explaining polymorphism.

Method Overloading and Polymorphism: solved examples

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

public class Test {
    static int area(int s) { return s * s; }
    static int area(int l, int b) { return l * b; }
    static double area(double r) { return 3.14 * r * r; }
    public static void main(String[] args) {
        System.out.println(area(5) + " " + area(4, 3) + " " + area(2.0));
    }
}

public class Test {
    static void show(int x) { System.out.println("int"); }
    static void show(double x) { System.out.println("double"); }
    public static void main(String[] args) {
        show(7);
        show('a');
        show(5L);
        show(3.5f);
    }
}

Where students lose marks in Method Overloading and Polymorphism

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

• ✗Mistake: Treating a different return type as an overload

  The compiler cannot tell the versions apart from a call.

  Wrong working

  int f(int a) and double f(int a) are overloaded

  Right working

  They have the same signature: compile-time error

  ✓Do this: Change the parameter list.

  Usually costs: 1 mark

• ✗Mistake: Matching long to the int version

  Widening goes upward only: long cannot be passed to an int parameter without a cast.

  Wrong working

  show(5L) prints int

  Right working

  show(5L) prints double (long widens to double)

  ✓Do this: Follow byte, short, int, long, float, double.

  Usually costs: 1 mark

• ✗Mistake: Writing overloaded method names with different spellings

  Overloading needs the exact same name.

  Wrong working

  sum() and sums()

  Right working

  sum() and sum(int a)

  ✓Do this: Keep the name identical.

  Usually costs: 1 mark

Practice questions on Method Overloading and Polymorphism

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 pair of methods is a valid example of overloading?
   (a) int f(int a) and void f(int a) (b) void f(int a) and void f(double a) (c) void f(int a) and void f(int b) (d) int f(int a) and int f(int a)

   Hint

   Look at the parameter types only.

   Answer

   (b) void f(int a) and void f(double a)

2. Q2 · 1 mark · Very short answerBoard level

   Which OOP principle is shown by method overloading?

   Hint

   One name, many forms.

   Answer

   Polymorphism.

3. Q3 · 2 marks · Short answerHarder board level

   Write the output:

   static void p(int a) { System.out.print("A"); }
   static void p(int a, int b) { System.out.print("B"); }
   static void p(double a) { System.out.print("C"); }
   // in main
   p(1);
   p(1, 2);
   p(1.5);
   p('x');

   Hint

   char widens to int before double.

   Answer

   ABCA

4. Q4 · 3 marks · Short answerHarder board level

   Write two overloaded methods named big: one that returns the larger of two ints and one that returns the larger of two doubles. State the values printed for big(3, 9) and big(2.5, 1.5).

   Hint

   Use if or the ternary operator.

   Answer

   static int big(int a, int b) { return a > b ? a : b; }
   static double big(double a, double b) { return a > b ? a : b; }
   big(3, 9) gives 9 and big(2.5, 1.5) gives 2.5.

5. Q5 · 1 mark · Assertion-reasonHOTS / competency

   Assertion (A): Changing only the return type of a method does not overload it.
   Reason (R): The compiler chooses an overloaded method using the name and the parameter list of the call.
   (a) Both A and R are true and R is the correct explanation of A. (b) Both A and R are true but R is not the correct explanation of A. (c) A is true but R is false. (d) A is false but R is true.

   Hint

   Does the call mention the return type?

   Answer

   (a) Both are true and R explains A.

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.What must differ in overloaded methods?Show answer

   The parameter list: number, types or order of types.

2. 2.Is overloading allowed with only a different return type?Show answer

   No.

3. 3.Which type does char widen to?Show answer

   int

4. 4.Which OOP principle does overloading illustrate?Show answer

   Polymorphism.

5. 5.What is an ambiguous call?Show answer

   A call where two versions fit equally well; it gives a compile-time error.

6. 6.Who decides which overloaded version runs?Show answer

   The compiler, from the arguments.

Method Overloading and Polymorphism: frequently asked questions