java 14-10-2023

package com.vq.classes;

class VQClassA {

public VQClassA(int x) {

this.x = x; }

protected int x; }

public class VQClassB extends VQClassA {

public VQClassB(int x, int x2, int y) {

super(x); x = x2; this.y = y; }

private VQClassB(int x, int y) {

super(x); this.x = x; this.y = y; }

private int x;

private int y;

public static void main(String[]args) {

VQClassA vqa = new VQClassA(10);

VQClassB vqb = new VQClassB(20, 10);

vqa = vqb;

System.out.println(vqa.x + " " + vqb.y); } }

• 10 10

• 10 20

• 20 20

• 20 10

Java is an object oriented programming language which where you declare the class which is type of object you just identified. The objects have states and behaviours which are methods in class.

• In java every thing is an object.

• A java program consists of objects which interact to each other by sending messages.

• An object can be build using other objects.

• All

You only want to declare the behaviour of a certain type without any implemention , you should declare it as interface. In its most common form, an interface is a group of related methods with empty bodies.

package com.vq.inheritance;

public interface VQCourse {

public void printCourseDetail();

public void getCoursePrice(); }

• VQJavaCourse extends VQCourse

• VQJavaCourse implements VQCourse

• Wrong Syntax.

Answer explanation

To implement this interface you'd use the implements keyword in the class declaration. Implementing an interface allows a class to become more formal about the behavior it promises to provide.

Which statement(s) is true about following program?

public class VirtuQCourseProvide {

public static void main(String[]args) {

String firstName = "VirtuQ";

String lastName = "Simplifying Education";

String FullName = firstName + lastName;

String courseProvider = FullName; }}

• The statement courseProvider==FullName will evaluate to true.

• The statement courseProvider.equals(FullName) will evaluate to true.

• The statement courseProvider.equals(courseProvider==firstName+lastName) will evaluate to true.

• The statement courseProvider.equals(courseProvider==firstName+lastName) will evaluate to false

Choose correct equivalent statement of following code.

int[][] arr = new int[3][];

for (int i = 0; i < arr.length; i++)

arr[i] = new int[3];

• int [][] arr = new int[3][];

• int [3][] arr = new int[3][];

• int [][3] arr = new int[3][];

• int [][] arr = new int[3][3];

Code below has class VQClassB which inherits another class VQClassA, study following code carefully and choose correct option about program output.

package com.vq.classes;

public class VQClassB {

class VQClassA {

public VQClassA(int x) {

this.x = x; } protected int x; }

public VQClassB(int x, int x2, int y) {

x = x2; this.y = y; }

private VQClassB(int x, int y) {

this.x = x; this.y = y; }

private int x;

private int y;

public static void main(String[]args) {

VQClassB vqb = new VQClassB(20, 10);

VQClassB.VQClassA vqa = new VQClassB(10, 10).new VQClassA(10);

System.out.println(vqa.x + " " + vqb.x); } }

• 10 10

• 10 20

• 20 20

• 20 10

class VQCourse {

public String courseName;

public int courseID; }

public class VirtuQCourseProvide {

public static void main(String[]args) {

VQCourse course1 = new VQCourse();

course1.courseID = 0001;

course1.courseName = "0001";

VQCourse course2 = new VQCourse();

course2 = course1;

System.out.println("course1.courseID = " + course1.courseID + ", course2.courseID = " + course2.courseID); }}

• course1.courseID = 0001 course2.courseID = 0001

• course1.courseID = course2.courseID = 1

• course1.courseID = 1, course2.courseID = 1

• course1.courseID = 0001, course2.courseID = 0001

ollowing program have compilation error, can you guess root cause of it?

abstract class VQCourse {

public String courseName;

public String courseID; }

public class VirtuQCourseProvide extends VQCourse {

public static void main(String[]args) {

VQCourse course1 = new VQCourse();

course1.courseID = "0001";

course1.courseName = "JAVA";

System.out.println(course1.toString()); }}

• Protected means only inherited class and class have access to protected members.

• abstract class VQCourse should have a implemented method.

• You cannot instantiate a abstract class.

• Declare class VQCourse as final.

Which of following statement(s) can result in new object instance creation if executed successfully.

• String str = new String();

• String str = new String("VirtuQ");

• String str = "VirtuQ" + " "+ Simplifying Education";

• int [] arr = {1,2,3,4,5};

• All

When is the object created with a new keyword?

• At run time

• At compile time

• Depends on the code

• None