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Core Java Interview Questions
Questions Answers Views Company eMail

Write the program numbers into words.For example 2345==two thousand three hundred fourty five

TCS,

2 7228

Sample code to retrieve objects from HashMap in sorted ascending order?

2 5234

Hi Friends, can u give code to convert ArrayList to HashMap and HashMap to ArrayList.

1 14836

Hi ,i convert contrller as jSp And presentation as servlet ...will it do? if so what are advantage and idsadvantages

IBM,

2 3687

what is java

Tech Mahindra,

3 4790

what is Inheritense

Tech Mahindra,

3 4747

what is multi-tasking

Anand Group, Photon Infotech, Tech Mahindra,

3 6172

what is multitherading

Tech Mahindra,

3 6689

What is Generic in java? Where can we write Generic ( class or method or objects or etc...)? with simple example? Thanks, Bose.

Infosys, Tech Mahindra,

2 18781

i need example for java abstraction. where we use abstraction and why we need abstraction.

Oracle,

2 12410

Consider that class classA, abstract class classB, and final classC have been defined.Which one of the following is correct? 1. classA extends classC implements classB 2. class A extends classB, classC 3. classA extends classB 4. classB implements classC

2 3860

Draw a UML class diagram for the code fragment given below: public class StringApplet extends Applet { private Label sampleString; private Button showTheString; private ButtonHandler bHandler; private FlowLayout layout; public StringApplet() { sampleString = new Label(" "); showTheString = new Button (" Show the String"); bHandler = new ButtonHandler(); layout = new FlowLayout(); showTheString.addActionListener(bHandler); setLayout(layout); add(sampleString); add(showTheString); } class ButtonHandler implements ActionListener { public void actionPerformed(ActionEvent e) { samplestring.setText("Good Morning"); } } } Note: The methods need not be indicated on the diagram.

1442

The following program reads data (details of students) from a file named students.txt and converts it into e-mail addresses. The results are written to a file named studentemail.txt. students.txt consists of a number of lines, each containing the data of a student in colon delimited format: Last Name:First Name:Student Number Each input record is converted to an e-mail address and written to studentemail.txt in the following format: the first character of the last name + the first character of the first name + the last four digits of the student number + “@myunisa.ac.za” import java.io.*; public class EmailConverter { public static void main(String[] args) throws IOException { BufferedReader input = new BufferedReader(new FileReader ("students.txt")); PrintWriter output = new PrintWriter(new FileWriter ("studentemail.txt")); String line = input.readLine(); while (line != null) { // Extract the information for each student String[] items = line.split(":"); // Generate the email address String email = "" + items[0].charAt(0) + items[1].charAt(0) + items[2].substring(4,8) + "@myunisa.ac.za"; email = email.toLowerCase(); // Output output.println(email); line = input.readLine(); } input.close(); output.close(); } } Rewrite the class so that it handles possible errors that may occur. In particular, it should do the following: • It should catch at least three appropriate exceptions that might occur, and display suitable messages. • At this stage, the program will not run correctly if there is an empty line in the input file. Change the program so that if an empty line is encountered, an exception is thrown and the empty line is ignored. This exception should be handled with the display of a suitable error message. • Before the e-mail address is added to the output file, check if the student number has 8 digits. If not, throw an InvalidFormatException (which the program should not handle itself)

1330

Say you want to store the information about a number of pets in an array. Typical information that you could store for each pet (where relevant) would be • Breed of animal • Animal's name • Its birth date • Its sex • Whether it has been sterilised or not • When it is due for its next inoculation • When it last had its wings clipped For each type of pet (eg. dog, cat or bird) you would typically define a class to hold the relevant data. Note: You do not need to implement these classes. Just answer the following questions. 3.1.1 What would be the advantage of creating a superclass (eg. Pet) and declaring an array of Pet objects over simply using an array of Objects, storing each of the instances of the different pet classes (eg. Dog, Cat or Bird) in it? 3.1.2 Would you define Pet as a class or as an interface? Why? (2) (2)

1182

3.2 Consider the following class: public class Point { protected int x, y; public Point(int xx, int yy) { x = xx; y = yy; } public Point() { this(0, 0); } public int getx() { return x; } public int gety() { return y; } public String toString() { return "("+x+", "+y+")"; } } Say you wanted to define a rectangle class that stored its top left corner and its height and width as fields. 3.2.1 Why would it be wrong to make Rectangle inherit from Point (where in fact it would inherit the x and y coordinates for its top left corner and you could just add the height and width as additional fields)? (1) 8 Now consider the following skeleton of the Rectangle class: public class Rectangle { private Point topLeft; private int height, width; public Rectangle(Point tl, int h, int w) { topLeft = tl; height = h; width = w; } public Rectangle() { this(new Point(), 0, 0); } // methods come here } 3.2.2 Explain the no-argument constructor of the Rectangle class given above. 3.2.3 Write methods for the Rectangle class to do the following: • a toString() method that returns a string of the format "top left = (x, y); height = h; width = w " where x, y, h and w are the appropriate integer values. • an above() method that tests whether one rectangle is completely above another (i.e. all y values of the one rectangle are greater than all y values of the other). For example, with the following declarations Rectangle r1 = new Rectangle(); Rectangle r2 = new Rectangle(new Point(2,2), 1, 4); the expression r2.above(r1) should give true, and r2.above (r2) should give false. (You can assume that the height of a rectangle is never negative.) (2) (5)

2198


Post New Core Java Questions

Un-Answered Questions { Core Java }

What is hash code collision?

423


What is the right data type to represent a price in java?

415


What is the collections api in java programming?

403


What is the use of bufferedreader?

395


What does %d do in java?

386






What is an empty list in java?

356


How many bits are used to represent unicode, ascii, utf-16, and utf-8 characters?

428


What is javac used for?

361


Why java is call by value?

391


there are N number of matchboxes numbered 1...N.each matchbox contain various number of stick.Two player can alternatevely pick some amount of stick from the higest stick containing box . The player is condidered win if there is no stick after his move.Find the final move so that the move player win. Note:In case the number of stick is equal ,pick the stick from the higest numbered box.

1427


What is static in java?

407


What is a conditional statement explain with example?

403


Explain when classnotfoundexception will be raised ?

427


Is string is a data type?

406


What is substring in java?

420