List of Topics/Techniques Important to Java

Binary Search [java]

Binary Search [java]
Authors Comments: Binary Search algorithm where the data is already defined



Quote
public class BinarySearch {



public static void main(String args[ ]) {





int []number= new int [10];

int NumberOfItems=10;

String output="";



number[0]=1;number[1]=2;number[2]=3; // populate array

number[3]=4;number[4]=5;number[5]=4;

number[6]=7;number[7]=8;number[8]=9;

number[9]=10;

int low=1;

int high=number.length;



//do processing



boolean found = false;



int input= Keyboard.getIntInRange(1,10,"enter number from 1-10" );

while(found==false){

int middle= getMiddle(low, high);

if (number[middle]==input){

found =true;

output="Found at Position " + middle;



}//end if

else{



if(number[middle]<input){

low=middle+1;

}//end if



else{

high=middle-1;

{



}//end else

}// end if



}//end for



}//end while



Screen.display(output,"Binary Search");





System.exit(0);



} // end of main







public static int getMiddle(int low, int high){

int middle = (low+high)/2;



return middle;

}//end getMiddle









} // end of class

Bubble Sort [java]

Bubble Sort [java]
Authors Comments: A bubble sort



Quote
public class BubbleSort {



public static void main(String args[ ]) {



int NumberOfItems=10;

int [] number= new int [NumberOfItems];

String output="";



// populate array



number[0]=7;number[1]=4;number[2]=1;

number[3]=2;number[4]=5;number[5]=8;

number[6]=3;number[7]=6;number[8]=10;

number[9]=9;



//do processing



for (int outer=9; outer>=0; outer--){

for (int inner=0; inner<9; inner++){

Compare (number,inner);

} // end for inner

} // end for outer



for (int i = 0; i<10 ; i++){

output += number + "n";

}//end for





Screen.display(output,"Sort");

System.exit(0);



} // end of main



public static void Compare (int [] number,int inner){

if (number[inner]>number[inner+1]){

int temp=number[inner];

number[inner]=number[inner+1];

number[inner+1]=temp;

} // end if

} // end Compare

} // end of class

Convert a hostname to the equivalent IP address [java]

Convert a hostname to the equivalent IP address [java]
Authors Comments: there is a mozilla addon that gives directly the ip of the website but i am giving an alternative in java code.




Quote
import java.net.InetAddress;

import java.net.UnknownHostException;



public class GetIP {

public static void main(String[] args) {

InetAddress address = null;

try {

address = InetAddress.getByName("enter the website's url here");

} catch (UnknownHostException e) {

System.exit(2);

}

System.out.println(address.getHostName() + "="

+ address.getHostAddress());

System.exit(0);

}

}

Decimal-Binary Converter (Simple) [java]

Decimal/Binary Converter (Simple) [java]
Authors Comments: This is a small snippet of code I wrote from scratch (as I do all my code). It takes keyboard input, and stores it as an Integer, where a small equation converts the decimal number into a "base 2" number (Binary).
I'm using a similar code snippet for a much larger program I'm working on.





Quote
import java.util.Scanner;



public class Binary

{

public static void main(String[] args)

{



int binaryOutput;



Scanner keyboard = new Scanner(System.in);



System.out.print("Enter a number: ");

binaryOutput = keyboard.nextInt();



System.out.println( Integer.toString( binaryOutput, 2 ));



}

}

File Editor [java]

File Editor [java]
Authors Comments: This program lets the user edit short text files in a window. A "File"
menu provides the following commands:

New -- Clears all text from the window.
Open -- Let's the user select a file and loads up to 100
lines of text form that file into the window. The
previous contents of the window are lost.
Save -- Let's the user specify an ouput file and saves
the contents of the window in that file.
Quit -- Closes the window and ends the program.

This class uses the non-standard classes TextReader and MessageDialog.




Quote

import java.io.*;

import java.awt.*;

import java.awt.event.*;



public class TrivialEdit extends Frame implements ActionListener {



public static void main(String[] args) {

// The main program just opens a window belonging to this

// TrivialEdit class. Then the window takes care of itself

// until the program is ended with the Quit command.

new TrivialEdit();

}





private TextArea text; // Holds that text that is displayed in the window.





public TrivialEdit() {

// Add a menu bar and a TextArea to the window, and show it

// on the screen. The first line of this routine calls the

// constructor from the superclass to specify a title for the

// window. The pack() command sets the size of the window to

// be just large enough to hold its contents.

super("A Trivial Editor");

setMenuBar(makeMenus());

text = new TextArea(20,60);

add(text, BorderLayout.CENTER);

pack();

show();

}





private MenuBar makeMenus() {

// Create and return a menu bar containing a single menu, the

// File menu. This menu contains four commands, and each

// command has a keyboard equivalent. The Frame will listen

// for action events from the menu.

Menu fileMenu = new Menu("File");

fileMenu.addActionListener(this);

fileMenu.add( new MenuItem("New", new MenuShortcut(KeyEvent.VK_N)) );

fileMenu.add( new MenuItem("Open...", new MenuShortcut(KeyEvent.VK_O)) );

fileMenu.add( new MenuItem("Save...", new MenuShortcut(KeyEvent.VK_S)) );

fileMenu.add( new MenuItem("Quit", new MenuShortcut(KeyEvent.VK_Q)) );

MenuBar bar = new MenuBar();

bar.add(fileMenu);

return bar;

}





public void actionPerformed(ActionEvent evt) {

// This will be called when the user makes a selection from

// the File menu. This routine just checks which command was

// selected and calls another routine to carry out the command.

String cmd = evt.getActionCommand();

if (cmd.equals("New"))

doNew();

else if (cmd.equals("Open..."))

doOpen();

else if (cmd.equals("Save..."))

doSave();

else if (cmd.equals("Quit"))

doQuit();

}





private void doNew() {

// Carry out the "New" command from the File menu by

// by clearing all the text from the TextArea.

text.setText("");

}





private void doSave() {

// Carry out the Save command by letting the user specify

// an output file and writing the text from the TextArea

// to that file.

FileDialog fd; // A file dialog that let's the user specify the file.

String fileName; // Name of file specified by the user.

String directory; // Directory that contains the file.

fd = new FileDialog(this,"Save Text to File",FileDialog.SAVE);

fd.show();

fileName = fd.getFile();

if (fileName == null) {

// The fileName is null if the user has canceled the file

// dialog. In this case, there is nothing to do, so quit.

return;

}

directory = fd.getDirectory();

try {

// Create a PrintStream for writing to the specified

// file and write the text from the window to that stream.

File file = new File(directory, fileName);

PrintWriter out = new PrintWriter(new FileWriter(file));

String contents = text.getText();

out.print(contents);

out.close();

}

catch (IOException e) {

// Some error has occured while opening or closing the file.

// Show an error message.

new MessageDialog(this, "Error: " + e.toString());

}

}





private void doOpen() {

// Carry out the Open command by letting the user specify

// the file to be opened and reading up to 100 lines from

// that file. The text from the file replaces the text

// in the TextArea.

FileDialog fd; // A file dialog that let's the user specify the file.

String fileName; // Name of file specified by the user.

String directory; // Directory that contains the file.

fd = new FileDialog(this,"Load File",FileDialog.LOAD);

fd.show();

fileName = fd.getFile();

if (fileName == null) {

// The fileName is null if the user has canceled the file

// dialog. In this case, there is nothing to do, so quit.

return;

}

directory = fd.getDirectory();

try {

// Read lines from the file until end-of-file is detected,

// or until 100 lines have been read. The lines are appended

// the the TextArea, with a line feed after each line.

File file = new File(directory, fileName);

TextReader in = new TextReader(new FileReader(file));

String line;

text.setText("");

int lineCt = 0;

while (lineCt < 100 && in.peek() != '') {

line = in.getln();

text.appendText(line + 'n');

lineCt++;

}

if (in.eof() == false)

text.appendText("nn********** Text truncated to 100 lines! ***********n");

in.close();

}

catch (Exception e) {

// Some error has occured while opening or closing the file.

// Show an error message.

new MessageDialog(this, "Error: " + e.toString());

}

}





private void doQuit() {

// Carry out the Quit command by exiting the program.

System.exit(0);

}





} // end class TrivialEdit

Java Higher lower [java]

Java Higher lower [java]
Authors Comments: More homework stuff. Theres probably better way of validating user input in java but since my class isnt there yet i cant use it so i came up with my own way. Good example of loops out the wazo.



Quote
package hilow;

import java.util.*;

public class hilow {



//Program plays higher lower with numbers 1-100

public static void main(String[] args) {





Scanner scan = new Scanner(System.in);



Random generator = new Random();



int user=1,comp,guesses=0, repeat=1;

String users;

char valid1,valid2,valid3;





//loop only executed first time and when game is won (Matched with first while)

do{

comp = generator.nextInt(100) + 1;

//loop only executed first time and while person is still guessing (Matched with second //while)



do{

//User input



System.out.println("Enter your guess 1-100 to end the game enter a negitive value");

System.out.println("All number beyond 3 digits will be trunacted to first 3 digits");

users = scan.nextLine();



//Checks to make sure the number doesnt start with anything other than a number

//

do{



valid1 = users.charAt(0);

if(valid1 > 57 || valid1 < 49)

{

System.out.println("No letters enter new number 1-100");

users = scan.nextLine();



}

}

while(valid1 > 57 || valid1 < 49);



int numLength = users.length();

//chop off digits beyond 3rd

if(numLength > 3)

{

users = users.substring(0,2);

}

//validate second digit if existant only runs when number is 2 digits

if(numLength == 2)

{

do{

valid2 = users.charAt(1);

if(valid2 > 57 || valid2 < 49)

{

System.out.println("No letters enter new number");

users = scan.nextLine();

}

}

while(valid2 > 57 || valid2 < 49);



}

if(numLength == 3)

{

do{

valid3 = users.charAt(2);

if(valid3 > 57 || valid3 < 48)

{

System.out.println("Letters only enter new number");

users = scan.nextLine();

}

}

while(valid3 > 57 || valid3 < 48);



}

//Takes value in users and turns it into a integer

user = Integer.parseInt(users);



//users number is greater than 100 so chose to quit

if(user > 100 || user < 1)

{



System.out.println("You choose to quit");

System.out.println("Press 1 if you wish to start again");

repeat = scan.nextInt();



//makes sure new sting is read in before validation

users = scan.nextLine();



}

//Checks If user guesses correctly and then ask if they want to play again

if(user == comp)

{

System.out.println("You win the number was " + comp);

guesses++;

System.out.println("It took you "+ guesses + " guesses");

System.out.println("Press 1 to play again");

repeat = scan.nextInt();

}

//users number is less than computer but still in acceptable range

if(user < comp && user > 0)

{

System.out.println("Your number is low");

guesses++;

}

//user greater than computers number but still inside acceptable range 1-100

if(user > comp && user < 101)

{

System.out.println("Your guess is high");

guesses++;

}



}

while(repeat == 1);

}

while(user != comp && user < 101);

}

}

Keyboard Class [java]

Keyboard Class [java]
Authors Comments: This is so that you can use JOption pane use the whole JOptionpane.showMessageDialog etc etc etc
instead you can use. Screen.Display();
Just a personal preference if you swing that way



Quote
It includes a method for.
getting a string
getting an int
getting an int in a range
getting a real



P.S
The code doesnt do anything on its own. It should complie only. Thats the whole point
// Keyboard Class



import javax.swing.JOptionPane;



public class Keyboard {



public static String getText(String intro) {

String textIn = JOptionPane.showInputDialog(intro);

return textIn;

}// end of getText()



public static int getInt(String intro) {

int intIn=0;

boolean ok=false;

do {

String intAsString = JOptionPane.showInputDialog(intro);

try {

intIn = Integer.parseInt(intAsString);

ok = true;

}// end of try

catch (NumberFormatException e) {

JOptionPane.showMessageDialog(null, "That was not an Integer!n");

}// end of catch

} while(!ok); // not an Integer

return intIn;

}// end of getInt()



public static int getIntInRange(int low, int high, String intro) {



int number = Keyboard.getInt(intro);

while ((number < low) || (number > high)) {

Screen.display("Value not in range " + low + " to " + high, "Ooopsie");

number = Keyboard.getInt(intro);

} // end while

return number;

} // end of method getIntInRange





public static double getReal(String intro) {

double realIn=0;

boolean ok = false;

do {

String realAsString = JOptionPane.showInputDialog(intro);

try {

realIn = Double.parseDouble(realAsString);

ok = true;

}// end of try

catch (NumberFormatException e) {

JOptionPane.showMessageDialog(null, "That is not a real number!n");

}// end of catch

} while (!ok); // not an Real

return realIn;

}// end of getReal()



public static boolean getOption(String intro) {

boolean option=false;

String input="";

while (!(input.equals("yes") || input.equals("no"))) {

input=getText(intro);

}

if (input.equals("yes")) {

option=true;

}

return option;

}// end of getOption()





} // end class

Logg

Math functions Quadratic Equation

[java] Math functions Quadratic Equation
Authors Comments: Solving quadratic equations.




Quote
import java.util.Scanner;



public class Quad

{



public static void main (String[] args)

{



int a, b, c; //ax^2 + bx + c

double discriminant, root1, root2;



Scanner read = new Scanner (System.in);



System.out.print ("Enter coefficient of x squared: ");

a = scan.nextInt();



System.out.print("Enter the coefficient of x: ");

b = scan.nextInt();



System.out.print("Enter the Constant: ");

c = scan.nextInt();



discriminant = Math.pow(b, 2) - (4 * a * c); //Math.pow power

root1= ((-1 * cool.gif + Math.sqrt(discriminant)) / (2 * a);

root2= ((-1 * cool.gif - Math.sqrt(discriminant)) / (2 * a); //Math.sqrt Squareroot



System.out.print("Root 1 is: " + root1);

System.out.print("Root 2 is: " + root2);



}

}

Selection Sort [java]

Selection Sort [java]
Authors Comments: Selection Sort in java with a defined array of numbers


Quote
public class SelectionSort {



public static void main(String args[ ]) {



int NumberOfItems=10;

int [] number= new int [NumberOfItems];

int [] empty= new int [NumberOfItems];

String output="";





// populate array



number[0]=7;number[1]=4;number[2]=1;

number[3]=2;number[4]=5;number[5]=8;

number[6]=3;number[7]=6;number[8]=10;

number[9]=9;



//do processing





for (int outer=0; outer<NumberOfItems; outer++){

int min=outer;

for (int inner=0; inner<NumberOfItems; inner++){

if (number[inner]<=number[min]){

min=inner;

}//end if

} // end for inner

empty[outer]=number[min];

number[min]=99;





} // end for outer



for (int i = 0; i<10 ; i++){

output += empty + "n";

}//end for





Screen.display(output,"Sort");

System.exit(0);



} // end of main







} // end of class

Simple read-write [java]

Simple read/write [java]
Authors Comments: A little program which reads in the content of a .txt file and outputs the content
to another .txt file but all in upper case.

It is very simple and just gives you an idea of one way to do read/write in java.

** This requires The Keyboard Class ( this is just a class with some JOption pane methods. it just makes life easier for me)**



Quote


import java.io.*;



class Ftest{

public static void main(String [] args){



String [] infile = new String [1];

infile[0] = Keyboard.getText("Choose file to read in")+".txt";

BufferedReader LINE;

PrintWriter OUT;

String PATH;

String PATHOUT = Keyboard.getText("Choose File name to write to")+".txt";; //set file name to write to

String data;

String output ="";



if (infile.length != 1){

System.out.println("Parameter is one filename"); // error report

return;

}// end if

PATH = infile[0];



try {//i/o may go wrong

LINE = new BufferedReader(new FileReader(PATH)); //input file handle

OUT = new PrintWriter(new FileWriter(PATHOUT)); //output file handle



while((data = LINE.readLine()) != null){ //read lines

data = data.toUpperCase();// change to uppr case

OUT.println(data);//write data to file



}// end while



LINE.close();

OUT.close();

Screen.display("Files have been writen and changed to upper case","Yay!");



}// end try

catch(IOException e){System.out.println("ACK!");} // error report

}// end main

}// end class

StreamdDemojava [java]

StreamdDemo.java [java]
Authors Comments: StreamDemo.java

this is just for begginers



Quote
import java.io.*;



public class StremDemo {

public static void main(String[] args) {

try {

System.out.print("input: ");

System.out.println("input matrix system: " +

System.in.red());

}

catch(IOException e) {

e.printStackTrace();

}

}

}

Very Basic Java

Very Basic Java
Authors Comments: Alright, this is the basic of the basics of Java. I decided to write one because theirs nothing in Java.

You can use whatever Java compiler you want. I use crimson editor.



Quote
public class test <--- naming your stuff

{



public static void main (String[] args) <-- your going to need this in every application

{

System.out.println("Hello World"); <-- println will display hello world

}

}





public class test

{



public static void main (String[] args)

{

String hello = "Hello World"; <-- This is where I'm signing Hello world to a String called hello

System.out.println(hello);

}

}

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