Java Tips – Series III
סקירה: זה 'טיפים Java' סדרה,,en,יש לנו בעיקר עבד על הידיים על קידוד חלק,,en,מטרת סדרה זו היא לעזור לך להבין את החלק קידוד ופרטים יישום,,en,ניסינו לכסות נושאים שונים יחד עם,,en,זיכרון ה- Java מנוהל על-ידי מודל הזיכרון.,,en, we have mainly worked on the hands-on coding part. The objective of this series is to help you understand the coding part and implementation details. We have tried to cover various topics along with coding examples. You will also like our Java series I ו - Java series II
1) How to display a clock using an applet?
A: The example has used String class and Calendar class to display the applet clock. Calendar class gives the value of ‘Hours’, ‘Minutes’ and ‘second’.
java.awt היבוא. *;
import java.applet.*;
import java.applet.*;
java.awt היבוא. *;
import java.util.*;
public class ClockApplet extends Applet implements Runnable{
Thread t,t1;
public void start(){
t = new Thread(this);
t.start();
}
public void run(){
t1 = Thread.currentThread();
בזמן(t1 == t){
repaint();
לנסות{
t1.sleep(1000);
}
לתפוס(InterruptedException דואר){}
}
}
public void paint(Graphics g){
Calendar cal = new GregorianCalendar();
String hour = String.valueOf(cal.get(Calendar.HOUR));
String minute = String.valueOf(cal.get(Calendar.MINUTE));
String second = String.valueOf(cal.get(Calendar.SECOND));
g.drawString(hour + “:” + minute + “:” + second, 20, 30);
}
}
Again you have to run the applet in a browser or applet viewer to check the output.
2) How to create an event listener in Applet?
A: Following example demonstrates how to create a basic Applet having buttons to add & subtract two numbers. Methods used here are addActionListener () to listen to an event(click on a button) & לַחְצָן() constructor to create a button.
import java.applet.*;
import java.awt.event.*;
java.awt היבוא. *;
public class EventListeners extends Applet
implements ActionListener{
TextArea txtArea;
String Add, Subtract;
אני int = 10, j = 20, sum =0,Sub=0;
public void init(){
txtArea = new TextArea(10,20);
txtArea.setEditable(false);
להוסיף(txtArea,”center”);
Button b = new Button(“Add”);
Button c = new Button(“Subtract”);
b.addActionListener(this);
c.addActionListener(this);
להוסיף(ב);
להוסיף(ג);
}
public void actionPerformed(ActionEvent e){
sum = i + j;
txtArea.setText(“”);
txtArea.append(“אני = “+ אני + “\t” + “j = ” + j + “\n”);
Button source = (לַחְצָן)e.getSource();
אם(source.getLabel() == “Add”){
txtArea.append(“Sum : ” + sum + “\n”);
}
אם(אני >j){
Sub = i – j;
}
אַחֵר{
Sub = j – אני;
}
אם(source.getLabel() == “Subtract”){
txtArea.append(“Sub : ” + Sub + “\n”);
}
}
}
3) How to open a link in a new window using Applet?
A: This example demonstrates how to open a particular webpage from an applet in a new window using showDocument() method with second argument as “_blank” .
import java.applet.*;
java.awt היבוא. *;
import java.net.*;
import java.awt.event.*;
public class testURL_NewWindow extends Applet
implements ActionListener{
public void init(){
String link_Text = “google”;
Button b = new Button(link_Text);
b.addActionListener(this);
להוסיף(ב);
}
public void actionPerformed(ActionEvent ae){
Button source = (לַחְצָן)ae.getSource();
String link = “http://www.”+source.getLabel()+”.com”;
לנסות {
AppletContext a = getAppletContext();
URL url = new URL(link);
a.showDocument(url,”_blank”);
}
לתפוס (MalformedURLException e){
שיטה(e.getMessage());
}
}
}
4) How to read a file using Applet?
A: The following code snippet demonstrates how to read a file using an Applet using openStream() method of URL. There are different ways to read a stream like buffered stream, customized buffered stream etc. Here we have used buffered stream to read the data.
import java.applet.*;
java.awt היבוא. *;
import java.io.*;
import java.net.*;
public class readFileApplet extends Applet{
String fileToRead = “test1.txt”;
StringBuffer strBuff;
TextArea txtArea;
Graphics g;
public void init(){
txtArea = new TextArea(100, 100);
txtArea.setEditable(false);
להוסיף(txtArea, “center”);
String prHtml = this.getParameter(“fileToRead”);
אם (prHtml != null) fileToRead = new String(prHtml);
readFile();
}
public void readFile(){
String line;
URL url = null;
לנסות{
url = new URL(getCodeBase(), fileToRead);
}
לתפוס(MalformedURLException e){}
לנסות{
InputStream in = url.openStream();
BufferedReader bf = new BufferedReader
(new InputStreamReader(ב));
strBuff = new StringBuffer();
בזמן((line = bf.readLine()) != null){
strBuff.append(line + “\n”);
}
txtArea.append(“File Name : ” + fileToRead + “\n”);
txtArea.append(strBuff.toString());
}
לתפוס(IOException דואר){
e.printStackTrace();
}
}
}
5) How to create different shapes using Applet?
A: This example demonstrates how to create an applet which will have a line, an Oval & a Rectangle using drawLine(), drawOval() and drawRect() methods of Graphics class. In java Graphics class is widely used to draw diagrams and those are used in pie chart, bar diagram etc.
import java.applet.*;
java.awt היבוא. *;
public class Shapes extends Applet{
int x=300,y=100,r=50;
public void paint(Graphics g){
g.drawLine(30,300,200,10);
g.drawOval(x-r,y-r,100,100);
g.drawRect(400,50,200,100);
}
}
The above code sample will produce the following result in a java enabled web browse
A line, Oval & a Rectangle will be drawn in the browser.
6) How to use swing applet in JAVA?
A: Swing is an important component in java to produce UI interfaces. These swing components are also used in applet to make the user interface.Following example demonstrates how to go use Swing Applet in JAVA by implementing ActionListener & by creating JLabels.
לייבא javax.swing. *;
import java.applet.*;
java.awt היבוא. *;
import java.awt.event.*;
public class SApplet extends Applet implements ActionListener {
TextField input,output;
Label label1,label2;
Button b1;
JLabel lbl;
int num, sum = 0;
public void init(){
label1 = new Label(“please enter number : “);
להוסיף(label1);
label1.setBackground(Color.yellow);
label1.setForeground(Color.magenta);
input = new TextField(5);
להוסיף(input);
label2 = new Label(“Sum : “);
להוסיף(label2);
label2.setBackground(Color.yellow);
label2.setForeground(Color.magenta);
output = new TextField(20);
להוסיף(output);
b1 = new Button(“Add”);
להוסיף(B1);
b1.addActionListener(this);
lbl = new JLabel(“Swing Applet Example. “);
להוסיף(lbl);
setBackground(Color.yellow);
}
public void actionPerformed(ActionEvent ae){
לנסות{
num = Integer.parseInt(input.getText());
sum = sum num;
input.setText(“”);
output.setText(Integer.toString(sum));
lbl.setForeground(Color.blue);
lbl.setText(“Output of the second Text Box : ”
+ output.getText());
}
לתפוס(NumberFormatException e){
lbl.setForeground(Color.red);
lbl.setText(“Invalid Entry!”);
}
}
}
7) How to write to a file using Applet?
A: In the following example java text area has been used to enter the user input. After entering the input it has been written in a file in local file system. The File () constructor has been used to create the file.
import java.io.*;
java.awt היבוא. *;
import java.awt.event.*;
לייבא javax.swing. *;
import java.applet.Applet;
import java.net.*;
public class WriteFile extends Applet{
Button write = new Button(“WriteToFile”);
Label label1 = new Label(“Enter the file name:”);
TextField text = new TextField(20);
Label label2 = new Label(“Write your text:”);
TextArea area = new TextArea(10,20);
public void init(){
להוסיף(label1);
label1.setBackground(Color.lightGray);
להוסיף(text);
להוסיף(label2);
label2.setBackground(Color.lightGray);
להוסיף(area);
להוסיף(לִכתוֹב,BorderLayout.CENTER);
write.addActionListener(new ActionListener (){
public void actionPerformed(ActionEvent e){
new WriteText();
}
}
);
}
public class WriteText {
WriteText(){
לנסות {
String str = text.getText();
אם(str.equals(“”)){
JOptionPane.showMessageDialog(אפס,
“Please enter the file name!”);
text.requestFocus();
}
אַחֵר{
File f = new File(str);
אם(f.exists()){
BufferedWriter out = new
BufferedWriter(FileWriter החדש(ו,נכון));
אם(area.getText().equals(“”)){
JOptionPane.showMessageDialog
(אפס,”Please enter your text!”);
area.requestFocus();
}
אַחֵר{
out.write(area.getText());
אם(f.canWrite()){
JOptionPane.showMessageDialog(אפס,
“Text is written in “+str);
text.setText(“”);
area.setText(“”);
text.requestFocus();
}
אַחֵר{
JOptionPane.showMessageDialog(אפס,
“Text isn’t written in “+str);
}
out.close();
}
}
אַחֵר{
JOptionPane.showMessageDialog
(אפס,”File not found!”);
text.setText(“”);
text.requestFocus();
}
}
}
לתפוס(Exception x){
x.printStackTrace();
}
}
}
}
8) How to print summation of n numbers?
A: Following example demonstrates how to add first n natural numbers by using the concept of stack. Here the static Stack class is used to hold the numbers. The custom stackAddition () method is used to add the numbers into the stack.
java.io.IOException יבוא;
public class AdditionStack {
static int num;
static int ans;
static Stack theStack;
הריק סטטי הראשי ציבורי(חוט[] ארגומנטים) throws IOException {
num = 50;
stackAddition();
שיטה(“Sum=” + ans);
}
public static void stackAddition() {
theStack = new Stack(10000);
ans = 0;
בזמן (num > 0)
{
theStack.push(num);
–num;
}
בזמן (!theStack.isEmpty())
{
int newN = theStack.pop();
ans = newN;
}
}
}
class Stack {
private int maxSize;
private int[] data;
private int top;
public Stack(int s) {
maxSize = s;
data = new int[maxSize];
top = -1;
}
public void push(int p) {
data[++top] = p;
}
public int pop() {
return data[top–];
}
public int peek() {
return data[top];
}
public boolean isEmpty() {
return (top == -1);
}
}
The above code sample will produce the following result.
Sum=1225
9) How to get the first and the last element of a linked list?
A: Following example shows how to get the first and last element of a linked list with the help of linkedlistname.getFirst() and linkedlistname.getLast() of LinkedList class. All of the stack/queue/deque operations could be easily recast in terms of the standard list operations. They’re included here primarily for convenience, though they may run slightly faster than the equivalent List operations.
import java.util.LinkedList;
public class Main {
הריק סטטי הראשי ציבורי(חוט[] ארגומנטים) {
LinkedList lList = new LinkedList();
lList.add(“100”);
lList.add(“200”);
lList.add(“300”);
lList.add(“400”);
lList.add(“500”);
שיטה(“First element of LinkedList is :
” + lList.getFirst());
שיטה(“Last element of LinkedList is :
” + lList.getLast());
}
}
The above code sample will produce the following result.
First element of LinkedList is: 100
Last element of LinkedList is: 500
10) How to add an element at first and last position of a linked list?
A: Following example shows how to add an element at the first and last position of a linked list by using addFirst() and addLast() method of Linked List class.
import java.util.LinkedList;
public class Main {
הריק סטטי הראשי ציבורי(חוט[] ארגומנטים) {
LinkedList lList = new LinkedList();
lList.add(“1”);
lList.add(“2”);
lList.add(“3”);
lList.add(“4”);
lList.add(“5”);
שיטה(lList);
lList.addFirst(“0”);
שיטה(lList);
lList.addLast(“6”);
שיטה(lList);
}
}
The above code sample will produce the following result.
1, 2, 3, 4, 5
0, 1, 2, 3, 4, 5
0, 1, 2, 3, 4, 5, 6
