Java Tips – Series III
Pregled: In this ‘Java Tips’ series, 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 in 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’.
Uvoz java.awt. *;
import java.applet.*;
import java.applet.*;
Uvoz java.awt. *;
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();
while(t1 == t){
repaint();
poskusite{
t1.sleep(1000);
}
ulova(InterruptedException e){}
}
}
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: Egzanp sa a demontre ki jan yo kreye yon Applet de baz ki gen bouton yo ajoute,,en,fè soustraksyon de chif,,en,Metòd yo itilize isit la se addActionListener,,en,koute yon evènman,,en,klike sou yon bouton,,en,konstriksyon pou kreye yon bouton,,en,piblik klas EventListeners fin aple,,en,aplike ActionListener,,en,TextArea txtArea,,en,Fisèl Ajoute,,en,Fè soustraksyon,,en,j =,,en,sòm = 0, Sub = 0,,en,txtArea = nouvo TextArea,,en,txtArea.setEditable,,en,sant,,en,Bouton b = nouvo bouton,,en,Ajoute,,en,Bouton c = nouvo bouton,,en,b.addActionListener,,en,c.addActionListener,,en,aksyon aksyon piblik la reyalize,,en,ActionEvent e,,en,sòm = mwen,,en,txtArea.setText,,en,txtArea.append,,en,Sous bouton =,,en,e.getSource,,pt,source.getLabel,,en,Sòm,,en,sòm,,en,Sub = i,,en,Sub = j,,en,Sub,,en,Ki jan yo louvri yon lyen nan yon nouvo fenèt lè l sèvi avèk Applet,,en,Egzanp sa a demontre ki jan yo louvri yon Paj Web patikilye soti nan yon applet nan yon nouvo fenèt lè l sèvi avèk showDocument,,en,metòd ak dezyèm agiman kòm,,en,enpòte java.net. *,,en & subtract two numbers. Methods used here are addActionListener () to listen to an event(click on a button) & Button() constructor to create a button.
import java.applet.*;
import java.awt.event.*;
Uvoz java.awt. *;
public class EventListeners extends Applet
implements ActionListener{
TextArea txtArea;
String Add, Subtract;
int i = 10, j = 20, sum =0,Sub=0;
public void init(){
txtArea = new TextArea(10,20);
txtArea.setEditable(false);
dodajte(txtArea,”center”);
Button b = new Button(“Add”);
Button c = new Button(“Subtract”);
b.addActionListener(this);
c.addActionListener(this);
dodajte(b);
dodajte(c);
}
public void actionPerformed(ActionEvent e){
sum = i + j;
txtArea.setText(“”);
txtArea.append(“i = “+ i + “\t” + “j = ” + j + “\n”);
Button source = (Button)e.getSource();
če(source.getLabel() == “Add”){
txtArea.append(“Sum : ” + sum + “\n”);
}
če(i >j){
Sub = i – j;
}
else{
Sub = j – i;
}
če(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.*;
Uvoz java.awt. *;
import java.net.*;
import java.awt.event.*;
klas piblik testURL_NewWindow fin aplike,,en,String link_Text =,,en,Google,,en,link_Text,,en,ActionEvent ae,,en,ae.getSource,,en,Lyen fisèl =,,en,www.,,en,AppletContext a = getAppletContext,,en,URL url = nouvo URL,,en,lyen,,en,a.showDocument,,en,MalformedURLException e,,en,Ki jan yo li yon dosye lè l sèvi avèk Applet,,en,Koupe kòd sa a demontre ki jan yo li yon dosye lè l sèvi avèk yon Applet lè l sèvi avèk openStream,,en,metòd URL la,,en,Gen diferan fason pou li yon kouran tankou koule tampon,,en,Customized buffered stream elatriye,,en,Isit la nou te itilize koule tampon pou li done yo,,en,klas piblik readFileApplet fin aplike,,en,File fileToRead =,,en,test1.txt,,en,StringBuffer strBuff,,en,String prHtml = this.getParameter,,en,fileToRead,,el,prHtml,,sl,fileToRead = nouvo chèn,,en,readFile,,en,anile piblik readFile,,en,Liy kòd,,en,URL url = nil,,en,url = nouvo URL,,en,getCodeBase,,en,InputStream nan = url.openStream,,en,BufferedReader bf = new BufferedReader,,en
implements ActionListener{
public void init(){
String link_Text = “google”;
Button b = new Button(link_Text);
b.addActionListener(this);
dodajte(b);
}
public void actionPerformed(ActionEvent ae){
Button source = (Button)ae.getSource();
String link = “http://www.”+source.getLabel()+”.com”;
poskusite {
AppletContext a = getAppletContext();
URL url = new URL(link);
a.showDocument(url,”_blank”);
}
ulova (MalformedURLException e){
Println(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.*;
Uvoz java.awt. *;
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);
dodajte(txtArea, “center”);
String prHtml = this.getParameter(“fileToRead”);
če (prHtml != null) fileToRead = new String(prHtml);
readFile();
}
public void readFile(){
String line;
URL url = null;
poskusite{
url = new URL(getCodeBase(), fileToRead);
}
ulova(MalformedURLException e){}
poskusite{
InputStream in = url.openStream();
BufferedReader bf = new BufferedReader
(new InputStreamReader(in));
strBuff = new StringBuffer();
while((line = bf.readLine()) != null){
strBuff.append(line + “\n”);
}
txtArea.append(“File Name : ” + fileToRead + “\n”);
txtArea.append(strBuff.toString());
}
ulova(IOException e){
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.*;
Uvoz java.awt. *;
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. Konpozan swing sa yo tou yo te itilize nan applet pou fè koòdone itilizatè a.,,en,pa kreye JLabels,,en,piblik klas SAplplet fin applet aplike ActionListener,,en,TextField D ',,en,Label label1, label2,,en,Bouton b1,,en,JLabel lbl,,en,Int num,,ar,label1 = nouvo etikèt,,en,tanpri antre nimewo,,en,label1,,en,label1.setBackground,,en,label1.setForeground,,en,Color.magenta,,en,D '= nouvo TextField,,en,label2 = nouvo etikèt,,en,label2,,en,label2.setBackground,,en,label2.setForeground,,en,pwodiksyon = nouvo TextField,,en,b1 = nouvo bouton,,en,b1.addActionListener,,en,lbl = new JLabel,,en,Egzanp Applet balanse,,en,lbl,,en,num = Integer.parseInt,,en,input.getText,,en,Mwen = mwen NUM,,la,input.setText,,en,output.setText,,en,Integer.toString,,en,lbl.setForeground,,en,Color.blue,,en,lbl.setText,,en,Sòti nan dezyèm bwat tèks la,,en,output.getText,,en,NumberFormatException e,,en,Antre Envalid,,en,Ki jan yo ekri nan yon dosye lè l sèvi avèk applet,,en & by creating JLabels.
uvoziti javax.swing. *;
import java.applet.*;
Uvoz java.awt. *;
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 : “);
dodajte(label1);
label1.setBackground(Color.yellow);
label1.setForeground(Color.magenta);
input = new TextField(5);
dodajte(input);
label2 = new Label(“Sum : “);
dodajte(label2);
label2.setBackground(Color.yellow);
label2.setForeground(Color.magenta);
output = new TextField(20);
dodajte(output);
b1 = new Button(“Add”);
dodajte(b1);
b1.addActionListener(this);
lbl = new JLabel(“Swing Applet Example. “);
dodajte(lbl);
setBackground(Color.yellow);
}
public void actionPerformed(ActionEvent ae){
poskusite{
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());
}
ulova(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.*;
Uvoz java.awt. *;
import java.awt.event.*;
uvoziti 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(){
dodajte(label1);
label1.setBackground(Color.lightGray);
dodajte(text);
dodajte(label2);
label2.setBackground(Color.lightGray);
dodajte(area);
dodajte(write,BorderLayout.CENTER);
write.addActionListener(new ActionListener (){
public void actionPerformed(ActionEvent e){
new WriteText();
}
}
);
}
public class WriteText {
WriteText(){
poskusite {
String str = text.getText();
če(str.equals(“”)){
JOptionPane.showMessageDialog(nič,
“Please enter the file name!”);
text.requestFocus();
}
else{
File f = new File(str);
če(f.exists()){
BufferedWriter out = new
BufferedWriter(Nova FileWriter(f,Res));
če(area.getText().equals(“”)){
JOptionPane.showMessageDialog
(nič,”Please enter your text!”);
area.requestFocus();
}
else{
out.write(area.getText());
če(f.canWrite()){
JOptionPane.showMessageDialog(nič,
“Text is written in “+str);
text.setText(“”);
area.setText(“”);
text.requestFocus();
}
else{
JOptionPane.showMessageDialog(nič,
“Text isn’t written in “+str);
}
out.close();
}
}
else{
JOptionPane.showMessageDialog
(nič,”File not found!”);
text.setText(“”);
text.requestFocus();
}
}
}
ulova(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.
Uvoz java.io.IOException;
public class AdditionStack {
static int num;
static int ans;
static Stack theStack;
public static void main(String[] args) throws IOException {
num = 50;
stackAddition();
Println(“Sum=” + ans);
}
public static void stackAddition() {
theStack = new Stack(10000);
ans = 0;
while (num > 0)
{
theStack.push(num);
–num;
}
while (!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 {
public static void main(String[] args) {
LinkedList lList = new LinkedList();
lList.add(“100”);
lList.add(“200”);
lList.add(“300”);
lList.add(“400”);
lList.add(“500”);
Println(“First element of LinkedList is :
” + lList.getFirst());
Println(“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 {
public static void main(String[] args) {
LinkedList lList = new LinkedList();
lList.add(“1”);
lList.add(“2”);
lList.add(“3”);
lList.add(“4”);
lList.add(“5”);
Println(lList);
lList.addFirst(“0”);
Println(lList);
lList.addLast(“6”);
Println(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
