my method "abc" return array of interface "xyz"
and "pqr" is abstract class implements abc
and class "jkl" extends pqr
My problem
1) when i call abc it retrun array xyz how can i do this
hint
xyz refer_xyz = new jkl();
but i can't create array.
2)I want to access method of jkl using reference of xyz??
What will happen inside init() in servlet. my interviewer
asked servlet lifecycle. i said "once servlet is loaded in
to memory init() will be called which performs servlet
initialization " . Again interview asked what values will be
initialized . what is difference between init() and
init(ServletConfig config).
I have a sorting issue with a Hashmap. My constraint is that
I MUST use the Hashmap and work with existing code. I do a
database query and place the results in a Hashmap. When I
iterate thru the Hashmap, it loses the original alphabetical
sorting done by the database. So, my problem is that I must
sort the results coming out of the Hashmap which is then
placed into another class.
Hi Friends, I am new to java. Can u explain about thread
concept.How i know one thread is locked, and how can i force
or acquire another thread for lock . Finally how to know
thread is released from lock. Explain types of lock(like
method level and block level) in thread.
Hi Friends, I am beginner in java. what i know about
synchonized keyword is,If more that one 1 thread tries to
access a particular resource we can lock the method using
synchronized keyword. Then after that how the lock is
released and how next thread access that.Please explain with
example.
Question 7 [8]
Consider the following class and answer the questions below
it:
public class StackWithGuard extends Stack {
public StackWithGuard(int size) {
super(size);
}
synchronized public boolean isEmpty() {
return super.isEmpty();
}
synchronized public boolean isFull() {
return super.isFull();
}
synchronized public int getSize() {
return super.getSize();
}
synchronized public void push(Object obj) {
try {
while (isFull()) {
wait();
}
} catch (InterruptedException e) {}
super.push(obj);
COS2144/102
11
notify();
}
synchronized public Object pop() {
try {
while (isEmpty()) {
wait();
}
} catch (InterruptedException e) {}
Object result = super.pop();
notify();
return result;
}
public static void main(String args[]) {
StackWithGuard stack = new StackWithGuard(5);
new Producer(stack, 15).start();
new Consumer(stack, 15).start();
}
}
Note: The Stack class is provided in the Appendix.
Note also: The following questions all refer to the pop()
method of the StackWithGuard
class given above.
7.1 What does the synchronized keyword ensure for this
method? (2)
7.2 Why is a while loop used to test whether the stack is
empty? In other words, why
wouldn't the following if statement be sufficient?
if (isEmpty()) {
wait();
}
(2)
7.3 Why is the result of popping (provided by the inherited
pop() method) stored in a
temporary variable? In other words, why wouldn't the
following statement be
sufficient?
return super.pop();
(2)
7.4 Why is the while loop placed in a try-catch structure?
(2)
Appendix
The LinkedQueue class:
public class LinkedQueue implements Queue {
private Node first, last;
private int count;
public LinkedQueue() {
first = last = null;
count =0;
}
public int size() {
return count;
}
public boolean isEmpty() {
return (count == 0);
12
}
public void enqueue(Object o) {
Node node = new Node();
node.element = o;
node.next = null;
node.prev = last;
if (last != null){
last.next = node;
}
else {
last = first = node;
}
last = node;
count++;
}
public void dequeue() {
if ((first!= null) & (first.next!=null)) {
first = first.next;
first.prev = null;
count--;
}
else {
first = last = null;
count--;
}
}
public Object front() {
return first;
}
}
class Node {
Object element;
Node next, prev;
}
The Stack class:
public class Stack {
protected Object rep[];
protected int top = -1;
protected int size = 0;
protected int count = 0;
public Stack(int size) {
if (size > 0) {
this.size = size;
rep = new Object[size];
}
}
public boolean isFull() {
return (count == size);
}
public boolean isEmpty() {
return (count == 0);
}
public int getSize() {
return size;
}
public void push(Object e) {
if (e != null && !isFull()) {
COS2144/102
13
top++;
rep[top] = e;
count ++;
}
}
public Object pop() {
Object result = null;
if (!isEmpty()) {
result = rep[top];
top--;
count--;
}
return result;
}
}
23
Question 5 [15]
Consider the following classes, illustrating the Strategy
design pattern:
import java.awt.*;
abstract class Text {
protected TextApplet tA;
protected Text(TextApplet tApplet) {
tA = tApplet;
}
abstract public void draw(Graphics g);
}
class PlainText extends Text {
protected PlainText(TextApplet tApplet) {
super(tApplet);
}
public void draw(Graphics g) {
g.setColor(tA.getColor());
g.setFont(new Font("Sans-serif", Font.PLAIN, 12));
g.drawString(tA.getText(), 20, 20);
}
}
class CodeText extends Text {
protected CodeText(TextApplet tApplet) {
super(tApplet);
}
public void draw(Graphics g) {
g.setColor(tA.getColor());
g.setFont(new Font("Monospaced", Font.PLAIN, 12));
g.drawString(tA.getText(), 20, 20);
}
}
public class TextApplet extends java.applet.Applet {
protected Text text;
protected String textVal;
protected Color color;
public String getText() {
return textVal;
}
public Color getColor() {
return color;
}
public void init() {
textVal = getParameter("text");
String textStyle = getParameter("style");
String textColor = getParameter("color");
if (textStyle == "code")
text = new CodeText(this);
else
text = new PlainText(this);
if (textColor == "red")
color = Color.RED;
else if (textColor == "blue")
color = Color.BLUE;
else
color = Color.BLACK;
}
public void paint(Graphics g) {
text.draw(g);
10
}
}
The Text class is more complicated than it should be (there
is too much coupling between the
Text and TextApplet classes). By getting rid of the
reference to a TextApplet object in the
Text class and setting the colour in the paint() method,
one could turn the Text class into an
interface and simplify the strategy classes considerably.
5.1 Rewrite the Text and PlainText classes to do what is
described above. (6)
5.2 Explain the consequent changes that are necessary to
the TextApplet class. (4)
5.3 Write an additional strategy class called FancyText (to
go with your simplified
strategy classes) to allow fancy text to be displayed for
the value "fancy" provided
for the style parameter. It should use the font Font
("Serif", Font.ITALIC, 12).
(3)
5.4 Explain what changes are necessary to the TextApplet
class for this. (2)
Create a form of user Login in JSP, that accepts the user
name and password from user and authenticate it with user
names and passwords stored in database.
(Plz provide me answer immediately)
34
How to solve the problem of generating the unique hash keys
with hash function?
63
EDS (Electronic Data Systems India Pvt Ltd) at Chennai on 16-12-2006.
Q1.A. Write note on “The class path Environment Variable”?
B. Which are different kinds of source code?
Q2.A. How to create an interface?
B. Why convert an applet to an application?
Q3.A. How to use Media tracker Class.
B. How to use string tokenizer class.
Q4 A. Explain the overview of UDP messaging.
B. Difference between SQL Exception class and SQL
Warning class.
Q5. A. How to create com object in Java?
B. Write short notes on “The properties class”
Q6. A. When object is created and destroyed?
B. Explain the JDB in depth & command line.
C. Write short notes on Web Sites.
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)
26
how to deploy tomcatserver to weblogic server?
write d following steps?
73
Difference between a Canvas and a Scroll Pane?.
79
Which Component subclass is used for drawing and painting?
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