25/03/25
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Q)What are the differences between Iterator and ListIterator?

Criteria                      Iterator                      ListIterator
************************************************
1)How to                   by calling                   by calling
get the refernce         iterator()                  listIterator()
of the cursor?            on collection              on collection

2)direction                unidirectional              bidirectional
of traversing

3)can be applied        any collection             only list based collection
to

4)operations             READ & DELETE           all CRUD operations
on collection
**************************************************************
Q)Example program on sorting of integers and Strings.
 //SortingTest1.java
import java.util.*;
class  SortingTest1{
	public static void main(String[] args){
		ArrayList<Integer> list1=new ArrayList<>();		
		Collections.addAll(list1,6,4,87,12,3,47);
		System.out.println("Before sorting:"+list1);	
		Collections.sort(list1);
		System.out.println("After sorting:"+list1);
		ArrayList<String> list2=new ArrayList<>();
		Collections.addAll(list2,"aunt","uncle","daughter","son","father","mom");
		System.out.println("Names before sorting:"+list2);
		Collections.sort(list2);
		System.out.println("Names after sorting:"+list2);
	}
}
Q)Example program on sorting of user defined objects(Employee instances)
//SortingTest2.java
import java.util.*;
class Employee {
	int empno;
	String name;
	double salary;
	Employee(int empno,String name,double salary){
		this.empno=empno;
		this.name=name;
		this.salary=salary;
	}
	public String toString(){
		return empno+"\t"+name+"\t"+salary;
	}//overridingng Object class method to display object's state in textual format
	
}//Employee
class  SortingTest2
{
	public static void main(String[] args)	{
		ArrayList<Employee> emps=new ArrayList<>();
		emps.add(new Employee(102,"Rama",70000));
		emps.add(new Employee(103,"Rahim",50000));
		emps.add(new Employee(101,"Salman",60000));
		System.out.println("Before sorting .......\n");
		for(Employee e:emps)
			System.out.println(e);
		Collections.sort(emps);
		System.out.println("After sorting .......\n");
		for(Employee e:emps)
			System.out.println(e);
	}
}

Note:- The above application causes compilation errors.
Reason:- Collections.sort() method performs sorting of collection of objects
if the objects are Comparable.

=>java.lang.Integer class and java.lang.String class  are Comparable. Therefore
their sorting was working in SortingTest1.java

Q)Explain about Comparable.
=>java.lang.Comparable is a functional interface(that has only one method).
=>This interface has the following abstract method.
         int   compareTo(T);//any type of element

=>Comparable interface imposes a total ordering on the objects of each class that implements
it. This ordering is referred to as the class' natural ordering and compareTo() method
is referred to as its natural comparision method.

=>compareTo() method is used to compare the current object with the specified object.
This method returns a +ve integer if the current object is greater than the specified object.
 It returns a -ve integer if the current object is lesser than the specified object. It returns
 zero if the current object is equal to the specified object.

Q)Example program on Comparable interface.
//ComparableApplication.java
import java.util.*;
class Employee implements Comparable<Employee> {
	int empno;
	String name;
	double salary;
	Employee(int empno,String name,double salary){
		this.empno=empno;
		this.name=name;
		this.salary=salary;
	}
	public String toString(){
		return empno+"\t"+name+"\t"+salary;
	}//overridingng Object class method to display object's state in textual format
	public int compareTo(Employee e){
		//return this.empno-e.empno;
		//return (int) (this.salary-e.salary);
		return this.name.compareTo(e.name);//sorting based on employee name
	}
}//Employee
class  ComparableApplication
{
	public static void main(String[] args)	{
		ArrayList<Employee> emps=new ArrayList<>();
		emps.add(new Employee(102,"Rama",70000));
		emps.add(new Employee(103,"Rahim",50000));
		emps.add(new Employee(101,"Salman",60000));
		System.out.println("Before sorting .......\n");
		for(Employee e:emps)
		   System.out.println(e);
		Collections.sort(emps);
		System.out.println("After sorting .......\n");
		for(Employee e:emps)
			System.out.println(e);
	}
}
Q)What are the limitations of Comparable interface  in sorting of the elements of a collection?
1)multiple sorting criteria can't be designed.
2)user defined object(element of colection object) is forced to implement
Comparable interface in order to be sorted.

Note:- java.util.Comparator interface overcomes these limitations.