22/01/25
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Q)What is the output of the following program?
class Student{
    int rollno;
    String name;
    Student(int rno,String nm){
         rollno=rno;
         name=nm;
    }
    void displayStudent(){
        System.out.println("ROLLNO:"+rollno);
        System.out.println("NAME:"+name);
    }
}//
class StudentApplication{
    public static void main(String a[]){
          Student s=new Student();
          s.displayStudent();
    }
 }//Student
Ans:- The above program causes compilation error.
Reason:- For Student class, zero argument constructor not available.
But in the syntax of Student object creation, we have used zero argument
constructor.

Q)What is constructor overloading?
=>Having multiple constructors within the same class with different parameters
is nothing but constructor overloading.

Q)Example Program on Constructor Overloading.
//BooksApplication.java
class Book{
	String title;
	String author;
	int pages;
	double price;
	Book(){
	    title="Java Complete Reference";
	    author="Herbert Schildt";
            pages=800;
	    price=650;
	}//non parameterised constructor
	Book(String t,String a,int p,double pr){
            title=t;
	        author=a;
	        pages=p;
	        price=pr;
	}
	void displayBookDetails(){
	    System.out.println("TITLE:"+title);
	    System.out.println("AUTHOR:"+author);
	    System.out.println("NO OF PAGES:"+pages);
	    System.out.println("PRICE Rs."+price);
	}
}
class ConstructorOverloadingApplication{
	public static void main(String[] args){
		Book b1=new Book();
		System.out.println("First book details.....");
		b1.displayBookDetails();
		Book b2=new Book();
		System.out.println("Second book details.....");
		b2.displayBookDetails();
		Book b3=new Book("Let us C","Yaswant Kanetakar",300,260);
		System.out.println("Third book details.....");
		b3.displayBookDetails();	    	
	}
}
Q)What is the output of the following program?
class Student{
    int rollno;
    String name;
    Student(int rollno,String name){
         rollno=rollno;
         name=name;
    }
    void displayStudent(){
        System.out.println("ROLLNO:"+rollno);
        System.out.println("NAME:"+name);
    }
}
class StudentApplication{
    public static void main(String a[]){
          Student s=new Student(101,"Rama");
          s.displayStudent();
    }
 }
 Ans:-
         ROLLNO:0
	 NAME:null
=>Reason for the unexpected output is
parameter names and instance variable names are the same.

=>Whenever instance variable name and parameter name are the same,
preference will be given to local variable only. Instance variable is not reffered.

=>To overcome the problem, we use "this" keyword.

Student(int rollno,String name){
         this.rollno=rollno;
         this.name=name;
    }
=>"this" is an implicit reference to the current object.

Q)What is constructor chaining?
=>Within the constructor of a class calling another constructor 
of the same class is nothing but constructor chaining.
=>It is done using "this" keyword.

class Employee{
	int empno;
	String name;
	Employee(){
	      System.out.println("Employee appointed");
	}
	Employee(int empno,String name){
		this();//zero argument constructor is called
		this.empno=empno;
		this.name=name;
		
	}
    void displayEmployee(){
		System.out.println("EMPNO:"+empno);
		System.out.println("NAME:"+name);
	}
	public static void main(String[] args) 
	{
		Employee e=new Employee(101,"Rama");
		e.displayEmployee();
	}
}

Q)Develop a Java application in which, two Distance objects(with the fields feet &inches )
are added and resultant distance is displayed.
class Distance{
	int feet;
	int inches;
	Distance(int feet,int inches){
		this.feet=feet;
		this.inches=inches;
	}
	void displayDistance(){
		System.out.println(feet+" feet "+inches+" inches");			
	}
	void addTwoDistances(Distance d1,Distance d2){
          int i=d1.inches+d2.inches;
		  int f=d1.feet+d2.feet;
		  if(i>=12){			  
			  feet++;
			  i=i-12;
		  }
		  Distance d=new Distance(f,i);
		  d.displayDistance();
		  
	}
}
class DistanceApplication{
	public static void main(String[] args) {
		Distance d1=new Distance(10,9);
		System.out.print("First distance is ");
		d1.displayDistance();
		Distance d2=new Distance(9,10);
		System.out.print("Second distance is ");
		d2.displayDistance();
		System.out.print("Resultant distance is ");
		d1.addTwoDistances(d1,d2);
	}
}