Overloading occurs when two or more methods in one class have the same method name but different parameters.
Overriding occurs when two methods have the same method name and parameters. One of the methods is in the parent class, and the other is in the child class. Overriding allows a child class to provide the specific implementation of a method that is already present in its parent class.
The two examples below illustrate their differences:
The table below highlights their key differences:
Must have at least two methods by the same name in the class.
Must have a different number of parameters.
If the number of parameters is the same, then it must have different types of parameters.
Overloading is known as compile-time polymorphism.
Must have at least one method by the same name in both parent and child classes.
Must have the same number of parameters.
Must have the same parameter types.
Overriding is known as runtime polymorphism.
Example codes
Overriding
Take a look at the code below:
class Dog{
public void bark(){
System.out.println("woof ");
}
}
class Hound extends Dog{
public void sniff(){
System.out.println("sniff ");
}
public void bark(){
System.out.println("bowl");
}
}
class OverridingTest{
public static void main(String [] args){
Dog dog = new Hound();
dog.bark();
}
}
In this overriding example, the dog variable is declared to be a Dog. During compile-time, the compiler checks if the Dog class has the bark() method. As long as the Dog class has the bark() method, the code compiles. At run-time, a Hound is created and assigned to dog, so, it calls the bark() method of Hound.
Overloading
Take a look at the code below:
class Dog{
public void bark(){
System.out.println("woof ");
}
//overloading method
public void bark(int num){
for(int i=0; i<num; i++)
System.out.println("woof ");
}
}
In this overloading example, the two bark methods can be invoked using different parameters. The compiler knows that they are different because they have different method signatures (method name and method parameter list).
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Java MCQs on overloading methods & argument passing in Java Programming Language. 1. What is the process of defining two or more methods within same class that have same name but different parameters
declaration? Answer: a 2. Which of these can be overloaded? Answer: c 3. Which of these is correct about passing an argument by call-by-value process? Answer: a 4. What is the process of defining a method in terms of itself, that is a method that calls itself? Answer: d 5. What will be the output of the following Java code?
a) method overloading
b) method overriding
c) method hiding
d) none of the mentioned
Clarification: Two or more methods can have same name as long as their parameters declaration is different, the methods are said to be overloaded and process is called method overloading. Method overloading is a way by which Java implements polymorphism.
a) Methods
b)
Constructors
c) All of the mentioned
d) None of the mentioned
Clarification: None.
a) Copy of argument is made into the formal parameter of the subroutine
b) Reference to original argument is passed to formal parameter of the subroutine
c) Copy of argument is made into the formal parameter of the subroutine and changes made on
parameters of subroutine have effect on original argument
d) Reference to original argument is passed to formal parameter of the subroutine and changes made on parameters of subroutine have effect on original argument
Clarification: When we pass an argument by call-by-value a copy of argument is made into the formal parameter of the subroutine and changes made on parameters of subroutine have no effect on original argument, they
remain the same.
a) Polymorphism
b) Abstraction
c) Encapsulation
d) Recursion
Clarification: None.
a) int float method
b) float int method
c) compile time error
d) run time error
Answer: c
Clarification: While resolving overloaded method, compiler automatically promotes if exact match
is not found. But in this case, which one to promote is an ambiguity.
6. What will be the output of the following Java code?
- class overload
- {
- int x;
- int y;
- void add(int a)
- {
- x = a + 1;
- }
- void add(int a, int b)
- {
- x = a + 2;
- }
- }
- class Overload_methods
- {
- public static void main(String args[])
- {
- overload obj = new overload();
- int a = 0;
- obj.add(6);
- System.out.println(obj.x);
- }
- }
a) 5
b) 6
c) 7
d) 8
Answer: c
Clarification: None.
output:
$ javac Overload_methods.java $ java Overload_methods 7
7. What will be the output of the following Java code?
- class overload
- {
- int x;
- int y;
- void add(int a)
- {
- x = a + 1;
- }
- void add(int a , int b)
- {
- x = a + 2;
- }
- }
- class Overload_methods
- {
- public static void main(String args[])
- {
- overload obj = new overload();
- int a = 0;
- obj.add(6, 7);
- System.out.println(obj.x);
- }
- }
a) 6
b) 7
c) 8
d) 9
Answer: c
Clarification: None.
output:
$ javac Overload_methods.java $ java Overload_methods 8
8. What will be the output of the following Java code?
- class overload
- {
- int x;
- double y;
- void add(int a , int b)
- {
- x = a + b;
- }
- void add(double c , double d)
- {
- y = c + d;
- }
- overload()
- {
- this.x = 0;
- this.y = 0;
- }
- }
- class Overload_methods
- {
- public static void main(String args[])
- {
- overload obj = new overload();
- int a = 2;
- double b = 3.2;
- obj.add(a, a);
- obj.add(b, b);
- System.out.println(obj.x + " " + obj.y);
- }
- }
a) 6 6
b) 6.4 6.4
c) 6.4 6
d) 4 6.4
Answer: d
Clarification: For obj.add(a,a); ,the function in line number 4 gets executed and value of x is 4. For the next function call, the function in line number 7 gets executed and value of y is 6.4
output:
$ javac Overload_methods.java $ java Overload_methods 4 6.4
9. What will be the output of the following Java code?
- class test
- {
- int a;
- int b;
- void meth(int i , int j)
- {
- i *= 2;
- j /= 2;
- }
- }
- class Output
- {
- public static void main(String args[])
- {
- test obj = new test();
- int a = 10;
- int b = 20;
- obj.meth(a , b);
- System.out.println(a + " " + b);
- }
- }
a) 10 20
b) 20 10
c) 20 40
d) 40 20
Answer: a
Clarification: Variables a & b are passed by value, copy of their values are made on formal parameters of function meth() that is i & j. Therefore changes done on i & j are not reflected back on original arguments. a & b remain 10 & 20 respectively.
output:
$ javac Output.java $ java Output 10 20
10. What will be the output of the following Java code?
a) 10 20
b) 20 10
c) 20 40
d) 40 20
Answer: b
Clarification: Class objects are always passed by reference, therefore changes done are reflected back on original arguments. obj.meth(obj) sends object obj as parameter whose variables a & b are multiplied and divided by 2 respectively by meth() function of class test. a & b becomes 20 & 10 respectively.
output: