300 Core java interview questions
151.
How can you add and remove nodes in Jtree?
// program
152.
What is the method to expand and collapse nodes in
a Jtree?
//program
153.
What is the use of JTable ?
Ans: JTree is a method to display hierarchical data
although it doesn't contain data while provide a simple view of data(
JTree displays its data vertically). Each row displayed by the tree
contains exactly one item of data, which is called a node.Each tree has
a root node from which all nodes descend.
154. What is meant by JFC ?
Ans: The Java Foundation Classes (JFC) are a graphical framework
for building portable
Java-based
graphical user interfaces (GUIs). The JFC
consists of the
Abstract Window Toolkit (AWT),
Swing and
Java 2D. Together, they provide a consistent
user interface for Java programs, regardless whether the underlying user
interface system is
Windows,
Mac OS X or
Linux.
155.
What is the class in Swing to change the
appearance of the Frame in Runtime?
Ans:
156.
How to reduce flickering in animation ?
157. What is meant by Javabeans ?
Ans: Java Beans( jsp:useBean)
is used for the purpose of reusable, platform-independent and portable to
create sophisticated application . Beans are dynamic generated hence easily
to customized.
JavaBeans (Syntax: <jsp:useBean id=" "
scope="page|request|session|application"
class=" "
type=" "
beanName=" "
/>)
id="beanInstanceName"
scope="page|request|session|application"
page: valid until page is complete.
request: bean instance lasts
for the client request.
session: bean lasts for
the client session.
application: bean instance created and lasts until application ends.
class & type ="package.class"
beanName="{package.class | <%= expression %>}".
158. What is JAR file ?
Ans: The main purpose of JAVA ARCHIVE( jar) file is store many file inside one
archive act as ZIP file. A .jar
file is generally used for distribute Java Application or libraries in the form
of classes, associated with metadata and resource such as test, image, doc, etc.
A JAR must contain manifest file locate in the path META-INF/MANIFEST.MF.
159. What is meant by manifest files ?
Ans: A manifest file is a specific file contained within a JAR archive
file, use to define extension and package related data. If a JAR file is
intended to be used as an executable file, the manifest file specifies the main
class of the application. The manifest file is named MANIFEST.MF.
160. What is Introspection in Java?
Ans: Introspection is the mechanism to
analyzing a bean's design patterns to reveal the bean's properties, events, and
methods, size, color etc. It controls the publishing of beans and discovery of
bean operations and properties. Introspection provide great advantage in beans
by implement two property which is-
- Reuse- Java Beans able to implementing the appropriate interfaces,
design conventions, and extending the appropriate classes provide the
reusability concept in program.
- Portability- Portability means write components once, reuse them
everywhere without extra specification means no platform-specific issues is
contend with component.
161.
What are the steps involved to create a bean ?
162. Say any two properties in Beans ?
Ans: Two property in Beans is--
- getProperty()
- setProperty()
163.
What is persistence in Java ?
Ans:
Two Type-- Beans Persistence and Java
Persistence API
164. What is the use of beanInfo ?
Ans: BeanInfo classes provides a high degree of control over how a bean
appears and behaves at design time. BeanInfo classes are design-time-only
classes. If a bean implementer wants to provide information regarding methods,
properties when they can provide a bean info class by implementing BeanInfo
interface and provide information regarding the bean properties, methods etc.
165. What are the interfaces you used in Beans ?
Ans: The Serializable interface is used in Beans.
166. What are the classes you used in Beans ?
Ans: Package.class.
167.
What is the difference between an Abstract class
and Interface?
Ans: Repeat
168. What is user defined exception ?
Ans: Use the following program--
/*
* Save as a FileUpload.java
* Program for Upload file content from a Text file.
* Use as a User Define Exception "File Not Found Exception"
*/
package r4r.co.in;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
public class FileUpload {
public static void main(String[] args) {
//File path store in file name
// String filename = "C:\\R4R\\waste.txt"; (Actual file Path and name)
/*
* Now for Generate Exception, just rename the file
* Command upper Syntax line, and use this
*/
String filename = "C:\\R4R\\wastage.txt"; //Fake file, for Generate Exception
String string = System.getProperty("LINE SEPRATOR:filename");
StringBuffer buffer = new StringBuffer();
try {
//File load into buffer
FileReader reader = new FileReader(filename);
BufferedReader br = new BufferedReader(reader);
//read single line from the file
System.out.println("Parameter from the file:");
String line;
while ((line = br.readLine()) != null) {
buffer.append(line).append(string);
System.out.println(line.toString());
}
} catch (IOException ioe) {
System.out.println("Exception Generate: " + ioe.getMessage());
}
}
}
Result: Exception Generate: C:\R4R\wastage.txt (The system cannot find the file specified)
169. What do you know about the garbage collector ?
Ans: Repeat
170. What is the difference between C++ & Java ?
Ans: Repeat
171. How do you communicate in between Applets & Servlets ?
Ans: Applet can communicate with servlet by using GET and POST
method, that means when applet is send data to servlet used GET method( must URL
encode, name and value) and receive value from POST method. URL connection work
as a bridge between applet and servlet.
Following syntax is used for such connection:-
//Establise a connection between applet and servlet
String location = "http:// ";
URL servlet = new URL(location);
URLConnection connection = servlet.openConnection();
//Bridge is ready to send data as output and receive input
connection.setDoInput(true);
connection.setDoOutput(true);
//Don't used catch version of URL connection
connection.setUseCaches(false);
connection.setDefaultUseCaches(false); //Use this also
//Send HTTP request for binary data transfer
connection.setRequestProperty("Content-Type", "value - the value associated with it");
//Now, Data is ready as input and output transfer
connection.getOutputStream();
172. What is the use of Servlets ?
Ans: Uses of the servlet is-
- Servlet is generally used for providing
dynamic content into web server.
- Servlet can able to access the large set of APIs available for the Java
platform.
- Servlet use a standard API that is supported by many Web servers.
- Servlet is loaded into once into memory can
called as many time as needed.
- Servlet is provide uniform API( Java
application programming interface) for maintaining session data from client
browser throughout Web server.
- Servlet can able to handle multiple request
concurrently in the synchronize manner.
173. In an HTML form I have a Button which makes us to open another page in 15 seconds. How will do you that ?
Ans: Use the following Program--
174. What is the difference between Process and Threads
?
Ans:
|
Process |
Threads |
- Thread is a program which defines a separate path of execution, the thread is the smallest unit of dispatchable code.
- Threads have direct access to the data segment of its process.
- Threads can directly communicate with other threads of its
process.
- Threads have almost no overhead because it is a single executed
program.
- Changes the behavior of main thread (cancellation, priority
change, etc.) may affect the other threads of the process.
|
- A process is a program that is executing.
- Processes have their own copy of the data segment of the parent
process.
- Processes generally use inter process communication to
communicate with sibling processes.
- processes have considerable overhead.
- Changes to the parent process doesn't affect its child
processes.
|
175. How will you initialize an Applet ?
Ans: Repeat
176. What is the order of method invocation in an
Applet ?
Ans: Applet’s life cycle methods is used in an Applet invocation--
- void init(): Initialization method called only once by the browser.
- void start(): Method called after init() and contains code to start
processing or stat the applet inside the browser.
- void stop(): Stops all processing started by start ().
- void destroy(): Called if current browser session is being terminated
and free all the resource by applet.
177. When is update method called ?
Ans: In Applet, whenever a screen needs redrawing (e.g., upon creation,
resizing, validating, and write) the update method is called. By default,
update method clears the screen and then calls the paint method, which normally
contains all the drawing code.
178. How will you communicate between two Applets ?
179. Have you ever used HashTable and Dictionary ?
180. What are statements in JAVA ?
Ans: In Java, Statements are a single
instruction in a program – a single unit of code. Consider the following
syntax:
package r4r.co.in;
public class R4R
{
public static void main(String[] args)
{
//single instruction in a program-- Statement
int age=40;
System.out.println("Age of Man is:" +age+"!");
}
}
181. What is JAR file ?
Ans: Repeat
182. What is Java Native Interface( JNI) ?
Ans: Java Native Interface (JNI) is a programming frame work that allows
Java code running in a Java Virtual Machine (JVM). It is use to call the
libraries written in other languages, such as C, C++ and assembly.
183. What is the base class for all swing components ?
Ans: All the swing components are derived from abstract javax.swing.JComponent class.
184. What is Java Foundation Classes (JFC) ?
Ans: Swing/ JFC is the primary Java Graphical User Interface( GUI)
widget toolkit, offers lightweight Java language specific GUI controls. It is consist of group of class, library
and services which add rich graphics functionality and
interactivity to Java applications.
185. What is Difference between AWT and Swing ?
Ans: Repeat -- Swing extends AWT by adding many components and
services.
186. Considering notepad/IE or any other thing as
process, What will Happen if you start notepad or IE 3 times? Where 3 processes
are started or 3 threads are started ?
187. How does thread synchronization occurs inside a
monitor?
Ans: A thread can acquire the lock for an object by using the
synchronized keyword. Each monitor is associated with an object reference. When
a thread arrives at the first instruction in a block of code it must obtain a
lock on the referenced object. The thread is not allowed to execute the code
until it obtains the lock. Once it has obtained the
lock, the thread enters the block of protected code. When the thread leaves the
block, no matter how it leaves the block, it releases the lock on the associated
object.
188. How will you call an Applet using a Java Script
function ?
Ans:
189. Is there any tag in HTML to upload and download
files ?
Ans: Use the following program-
<html>
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body>
<H1>Use as a upload file from system</H1>
<form name="form" method="post" enctype="multipart/form-data" action="FileName">
<BR>
<input type="file" name="file" value="" size="30" />
<BR><BR>
<input type="Button" value=" SubmitDocument " name="Submit" >
</form>
</body>
</html>
190. Why do you Canvas ?
Ans: Canvas class belongs to the java.awt package. It is a rectangular area on which something
drawing by using the methods of java.awt.Graphics.
The Canvas class has only three methods:
- public Canvas()
- public void addNotify()
- public void paint(Graphics graphic)
191. How can you push data from an Applet to Servlet ?
Ans: Repeat --Similar
to communicate in between Applets & Servlets
192. What are the benefits of Swing over AWT ?
Ans: Repeat
193. Where the CardLayout is used ?
Ans: CardLayout is unique in all other layout managers because it's
class is used for switch between two panels. The CardLayout class manages two or
more components (usually JPanel instances) that share the same display space and
allow user to choose between the components by using a combo box.
194. What is the Layout for ToolBar ?
Ans: The layout for Toolbar is Flow Layout.
195. What is the difference between GridLayout and GridbagLayout ?
Ans: GridLayout class allow to all the components in a rectangular grid
like structure of container. The container is divided into an equal sized
rectangles and each component is placed inside a rectangle.
The GridBagLayout class is a flexible layout
manager that aligns components vertically and horizontally, without requiring
that the components be of the same size. Each GridBagLayout object maintains a
dynamic, rectangular grid of cells, with each component occupying one or more
cells, called its display area.
196. How will you add panel to a Frame ?
Ans: Use the following Program--
/*
* Save as a newFrame.java
* Program dispaly JPanel add to JFrame
*/
package r4r.co.in;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class newFrame extends javax.swing.JFrame {
private JLabel lable;
public newFrame() {
JFrame frame = new JFrame("Frame that hold JPanel");
JPanel panel = new JPanel();
frame.setVisible(true);
frame.setSize(400, 200);
panel.setLayout(null);
lable = new JLabel("Lable add inside a panel");
lable.setBounds(50, 10, 140, 30);
//Lable add into frame
panel.add(lable);
//Add panel into Frame
frame.getContentPane().add(panel);
}
public static void main(String[] args) {
JFrame frame = new newFrame();
}
}
Output:
197. What is the corresponding Layout for Card in Swing
?
Ans: The corresponding Layout for Card in Swing CardLayout.
198. What is light weight component ?
Ans:Repeat
199. What is bean ? Where it can be used ?
Ans:Repeat
200. What is difference in between Java Class and Bean ?
500 Java Objective Questions and Answer
