ArrayList names = new ArrayList(); names.add(\"Ahmed\"); names.add(\"Khalid\");

Question

ArrayList names = new ArrayList(); names.add("Ahmed"); names.add("Khalid"); names.add("Faris"); names.set(1, "Muhammad"); Consider the above code snippet. What is the output of each of the following: System.out.println(names.get(1)); System.out.println(names.size()); System.out.println(names.get(names.size()-1)); System.out.println(names.get(3)); Write a program that reads students information from the user. Your program must have 2 classes: Class named (Students) that have: Two instance variables: Student ID and Student name and (Choose a good type for each of them). Methods for creating a new student (constructor) >>return information from existing instance (getter methods). Runner class named as (StudentsRunner) that gets student information from the user and stores it. The program must give the user the ability to stop inserting new values. After the user finish inserting, the program prints the entire list (using for each loop). The following is a typical run of the program: Enter Student IDs123456 Enter Student nameAhmad The student info has been stored insert Q to quit t Enter Student IDs98765 Enter Student nameAbdulrahman The student info has been stored insert Q to quitq student #1 the student ID: s123456 the student name: Ahmad student #2 the student ID: s98765 the student name: Abdulrahman

Explanation / Answer

Q1) initial the arraylist names will be empty

Initial size of names will be '0'

names.add("Ahmed") implies the first element of names will be :Ahmed

names.add("Khalid")

names.add("Faris")

After these three statements the array list will contain the following elements

Elements index

Ahmed 0

Khalid 1

Faris 2

4th instruction names.set(1,"Muhammad")   this will update the 2nd element i.e the element at the index 1

after executing this statement the names arraylist will be updated as

Elements index

Ahmed 0

Muhammad 1

Faris 2

Answers:

i)System.out.println(names.get(1)) get(int index) method will retrieve the value present at the specified index which is provided in the get method

   output :Muhammad the value present at index 1 is muhammad

ii)System.out.println(names.size()) // size() method will return the number of elements present in the arraylist

output : 3

iii)System.out.println(names.get(names.size()-1))

names.get(names.size()-1) we have names.size() =3

names.get(3-1) = names.get(2) // which will return the value present at the index '2'

output:Faris

iv)System.out.println(names.get(3))

output:java.lang.IndexOutOfBoundsException since we have idex till 2 so we are trying to access the element which is not defined and no index of 3.

Question 2)

1) public class Students {

private int studentId; // variable for student id

private String studentName; // variable for student name

Students(int id, String name){ //constructor with 2 parameters id and name

student name and student id cant be null in case if we get any null values exception will be raised

this.studentId=id;

this.studentName=name;

}// end of constructor

}// end of class Students.

2) public class StudentsRunner{

public static void main(String[] args){

int id;

String name;

char forquit;

List<Students> students=new ArrayList<Students>();

while(forquit!= 'q' or forquit!='Q'){

System.out.println("Enter Student Id");

id=sc.nextInt();

sc.nextLine();

System.out.println("Enter Student Name");

name=sc.nextLine();

Students s= new Students(id,name);

s.getdata();

students.add(s);

System.out.println("The student info has been stored");

System.out.println("insert Q to quit);

   forquit=sc.nextLine();

}

}

}

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