Java Tips – Series III
Преглед: 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 и 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’.
импорт јава.авт *.;
import java.applet.*;
import java.applet.*;
импорт јава.авт *.;
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();
пробати{
t1.sleep(1000);
}
улов(ИнтерруптедЕкцептион е){}
}
}
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.*;
импорт јава.авт *.;
public class EventListeners extends Applet
implements ActionListener{
TextArea txtArea;
String Add, Subtract;
инт и = 10, j = 20, sum =0,Sub=0;
public void init(){
txtArea = new TextArea(10,20);
txtArea.setEditable(false);
додати(тктАреа,”center”);
Button b = new Button(“Add”);
Button c = new Button(“Subtract”);
b.addActionListener(this);
c.addActionListener(this);
додати(б);
додати(ц);
}
public void actionPerformed(ActionEvent e){
sum = i + j;
txtArea.setText(“”);
txtArea.append(“и = “+ ја + “\t” + “j = ” + j + “\н”);
Button source = (Button)e.getSource();
ако(source.getLabel() == “Add”){
txtArea.append(“Sum : ” + sum + “\н”);
}
ако(ја >j){
Sub = i – j;
}
else{
Sub = j – ја;
}
ако(source.getLabel() == “Subtract”){
txtArea.append(“Sub : ” + Sub + “\н”);
}
}
}
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.*;
импорт јава.авт *.;
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);
додати(б);
}
public void actionPerformed(ActionEvent ae){
Button source = (Button)ae.getSource();
String link = “хттп://www.”+source.getLabel()+”.com”;
пробати {
AppletContext a = getAppletContext();
URL url = new URL(link);
a.showDocument(url,”_blank”);
}
улов (MalformedURLException e){
Систем.оут.принтлн(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.*;
импорт јава.авт *.;
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);
додати(тктАреа, “center”);
String prHtml = this.getParameter(“fileToRead”);
ако (prHtml != null) fileToRead = new String(prHtml);
readFile();
}
public void readFile(){
String line;
URL url = null;
пробати{
url = new URL(getCodeBase(), fileToRead);
}
улов(MalformedURLException e){}
пробати{
InputStream in = url.openStream();
BufferedReader bf = new BufferedReader
(new InputStreamReader(in));
strBuff = new StringBuffer();
while((line = bf.readLine()) != null){
strBuff.append(line + “\н”);
}
txtArea.append(“File Name : ” + fileToRead + “\н”);
txtArea.append(strBuff.toString());
}
улов(ИОЕкцептион е){
е.принтСтацкТраце();
}
}
}
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.*;
импорт јава.авт *.;
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.
увоз јавак.свинг *.;
import java.applet.*;
импорт јава.авт *.;
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 : “);
додати(label1);
label1.setBackground(Color.yellow);
label1.setForeground(Color.magenta);
input = new TextField(5);
додати(input);
label2 = new Label(“Sum : “);
додати(label2);
label2.setBackground(Color.yellow);
label2.setForeground(Color.magenta);
output = new TextField(20);
додати(output);
b1 = new Button(“Add”);
додати(b1);
b1.addActionListener(this);
lbl = new JLabel(“Swing Applet Example. “);
додати(lbl);
сетБацкгроунд(Color.yellow);
}
public void actionPerformed(ActionEvent ae){
пробати{
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());
}
улов(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.*;
импорт јава.авт *.;
import java.awt.event.*;
увоз јавак.свинг *.;
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(){
додати(label1);
label1.setBackground(Color.lightGray);
додати(text);
додати(label2);
label2.setBackground(Color.lightGray);
додати(area);
додати(write,BorderLayout.CENTER);
write.addActionListener(new ActionListener (){
public void actionPerformed(ActionEvent e){
new WriteText();
}
}
);
}
public class WriteText {
WriteText(){
пробати {
String str = text.getText();
ако(str.equals(“”)){
JOptionPane.showMessageDialog(нула,
“Please enter the file name!”);
text.requestFocus();
}
else{
File f = new File(str);
ако(f.exists()){
BufferedWriter out = new
BufferedWriter(Нови ФилеВритер(Ф,прави));
ако(area.getText().equals(“”)){
JOptionPane.showMessageDialog
(нула,”Please enter your text!”);
area.requestFocus();
}
else{
оут.врите(area.getText());
ако(f.canWrite()){
JOptionPane.showMessageDialog(нула,
“Text is written in “+str);
text.setText(“”);
area.setText(“”);
text.requestFocus();
}
else{
JOptionPane.showMessageDialog(нула,
“Text isn’t written in “+str);
}
оут.цлосе();
}
}
else{
JOptionPane.showMessageDialog
(нула,”File not found!”);
text.setText(“”);
text.requestFocus();
}
}
}
улов(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.
увоз јава.ио.ИОЕкцептион;
public class AdditionStack {
static int num;
static int ans;
static Stack theStack;
публиц статиц воид маин(Ниска[] аргс) throws IOException {
num = 50;
stackAddition();
Систем.оут.принтлн(“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 {
публиц статиц воид маин(Ниска[] аргс) {
LinkedList lList = new LinkedList();
lList.add(“100”);
lList.add(“200”);
lList.add(“300”);
lList.add(“400”);
lList.add(“500”);
Систем.оут.принтлн(“First element of LinkedList is :
” + lList.getFirst());
Систем.оут.принтлн(“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 {
публиц статиц воид маин(Ниска[] аргс) {
LinkedList lList = new LinkedList();
lList.add(“1”);
lList.add(“2”);
lList.add(“3”);
lList.add(“4”);
lList.add(“5”);
Систем.оут.принтлн(lList);
lList.addFirst(“0”);
Систем.оут.принтлн(lList);
lList.addLast(“6”);
Систем.оут.принтлн(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
