What you do to learn the basics of Java??
Java is one of the pure object oriented programming language where all concepts are from C++ and syntax is from C.It is easy for one to learn java and get into IT porvided you have good interest for programming.But of-course Java is an ocean and unlike .Net, Java has its own advantages.
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Applet programming with java-Interview preparation
APPLETS
•
Applets
are small applications that are accessed
on an internet server, transported over the Internet, automatically installed,
and run as a part of a web document.
•
Applets
must be run under an appletviewer or a java compatible browser.
Life Cycle of an Applet
Ø init()
Ø start()
Ø paint()
Ø stop()
Ø destroy()
init()
Ø The init() method is the first method
to be called and where variables are initialised.
Ø
This method is called only once during
the run time of the applet.
start()
Ø The
start() method is called
after init().
Ø It
is also called to restart an
applet after it has been stopped.
•
paint()
This method is called each time the
applet’s output must be redrawn.
•
stop()
This method is called when a web browser
leaves the HTML document containing the applet.
destroy()
Ø The destroy() method is called when
the environment determines that the applet need to be removed completely from
memory.
Ø At this point, the user should free
up any resources the applet may be using.
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Applet Fundamentals
import java.awt.*;
import java.applet.*;
/*
<applet
code="simpleapplet" width=200 height=200>
</applet>
*/
public class simpleapplet extends Applet {
public void paint(Graphics
g) {
g.drawString(“A
simple Applet”,20,20);
}
}
•
Applets
interact with the user through the AWT, not through the console-based I/O
classes.
•
It
imports two packages.
•
paint()
is defined by AWT and must be overridden by the applet.
•
The
paint() method has one parameter of type Graphics. This contains the graphic
context, which describes the graphics environment in which the applet is
running.This context is used whenever output to the applet is required.
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Graphics:
•
Graphics class provides methods for drawing simple
geometric shapes, text, and images to the graphics destination.
•
All
of the graphics-related operations on a component or image occur via one of
these methods.
The
Graphics class provides two methods that draw text on a component or an image
•
void
drawString(String str, int x, int y)
•
void
drawChars(char [] data, int offset, int length, int x, int y)
void drawString(String message, int x, int y)
Ø drawString() is a member of Graphics class
Ø This method outputs the string.
public void
paint(Graphics g)
{
g.drawString("abc", 25, 25);
}
public void
paint(Graphics g)
{
char [] rgc = { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j'
};
g.drawChars(rgc, 0, 5, 25, 25);
g.drawChars(rgc, 5, 5, 25, 50);
}
Running an Applet
<applet
code="AnotherHello.class" width="300"
height="150">
</applet>
Ø
This tells
the browser to run the applet AnotherHello.class, and to use an area of the
screen 300 pixels wide and 150 high.
The HTML Applet Tag
<APPLET
[CODEBASE=codebase URL]
CODE=appletName
[ALT=alternateText]
[NAME=appletInstance Name]
[ALGN=alignment]
[USPACE=pixels]
[HSPACE=pixels]
>
[<PARAM
NAME=attributeName VALUE=value>]
</APPLET>
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Typical
parameters for an applet would be:
•
color
used by the applet
•
font
and font size to be used on text in the applet
•
name
of an image file to be inserted in the applet
Drawing Lines
g.drawLine(x1,
y1, x2, y2);
Ø where
(x1, y1) and (x2, y2) are the endpoints of your lines
Drawing Rectangles
public void
drawRect(int x, int y, int width, int height);
Ø the first int is the left hand side of the
rectangle, the second is the top of the rectangle, the third is the width and
the fourth is the height.
Ovals and Circles
•
public
void drawOval(int left, int top, int width, int height)
•
public
void fillOval(int left, int top, int width, int height)
•
public
void drawArc(int left, int top, int width, int height, int startAngle, int
stopAngle)
•
public void fillArc(int left, int top, int
width, int height, int startAngle, int stopAngle)
Color
•
Color
medGray = new Color(127, 127, 127);
•
Color
cream = new Color(255, 231, 187);
•
Color
lightGreen = new Color(0, 55, 0);
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Question asked in Capgemini interview for our fresher student!!
What are the methods in thread class??
static
methods:
activeCount();
currentThread();
sleep();
yield();
instance
methods:
getPriority();
setPriority();
start();
stop();
run();
isAtive();
suspend();
resume();
join();
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Static Methods of Thread
Class
•
static int activeCount() - returns the number of currently
active threads. For example:
- num_
threads = Thread. activeCount();
•
static Thread currentThread() - returns the object corresponding
to the currently executing thread (self reference)
- Thread
myself = Thread. currentThread();
•
static void sleep( long millis) throws InterruptedException -
this causes the current thread to
sleep for the specified
amount of time. Other threads will
run at this time.
•
You can also specify the number of nanoseconds as well
- static
void sleep(long millis, int nano);
•
static void yield() - causes the thread to yield the processor
to any other waiting threads -
Java
does not guarantee preemption, you should use this to
ensure fairness.
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Instance
Methods of Thread Class
•
These methods control the thread represented by a Thread
object
•
int getPriority() - returns the threads priority - a value
between Thread. MIN_ PRIORITY and
Thread. MAX_ PRIORITY
•
void setPriority( int newpri)
- this
sets the threads priority
- high
priority threads will preempt lower ones when they become ready to run.
Thread myself =
Thread. currentThread();
myself. setPriority(
Thread. MAX_ PRIORITY);
•
A ThreadGroup may restrict the maximum priority of all its
member threads - therefore the
setPriority method may not
succeed.
•
void start() throws IllegalThreadStateException - actually
starts the thread - the thread
starts and enters the run() method
•
void stop() throws SecurityException - stops the thread
•
void run() - this method is called when the thread is started.
•
This is what the thread will execute while it is alive.
•
boolean isAlive() - returns a value indicating whether the
thread is currently alive - i.e.
Started more recently and has not yet
been died.
•
void suspend() - suspends the threads execution
•
void resume() - resumes the execution of the thread
•
void join() – causes the caller to wait until the thread dies
http://www.metaforumtechnologies.com/java-j2ee-training-in-chennai.html
http://www.metaforumtechnologies.com/java-j2ee-training-in-chennai.html
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Applet creation in java-video tutorials
Inheritance in java