Java

About Java programming language!

Java is an object-oriented programming language.
Java is compiled and interpreted.
Java programming language has the following advantages: simplicity, portability, platform independence, object orientation, high security, high performance.

Java is a programming platform that includes the following features:

Java programming language
Compiler
A virtual machine called the Java Virtual Machine(JVM)
A class library

Object-oriented programming features are:

Abstraction
Encapsulation
Inheritance
Polymorphism

The main chapters of this tutorial are:

First Java Example

public class JavaExample{
    public static void main(String [] args){
        System.out.println("This is an Java example");
    }
}

Java Swing

The main classes of the swing package are:

JApplet
JButton
JCheckBox
JCheckBoxMenuItem
JColorChooser
JComboBox
JComponent
JDesktopPane
JDialog
JFileChooser
JFormattedTextField
JFrame
JInternalFrame
JLabel
JList
JMenu
JMenuBar
JMenuItem
JOptionPane
JPanel
JPasswordField
JPopupMenu
JProgressBar
JRadioButton
JRadioButtonMenuItem
JSlider
JScrollBar
JScrollPane
JSeparator
JTable
JTextArea
JTextComponent
JTextField
JToggleButton
JTree
JWindow
Timer

Java AWT

The main classes of the java awt package are:

BorderLayout
Button
Canvas
Checkbox
CheckboxGroup
CheckboxMenuItem
Choice
Color
Component
Container
Dialog
Dimension
FileDialog
FlowLayout
Font
Frame
Graphics
GridBagLayout
GridLayout
Image
ImageCapabilities
Label
List
Menu
MenuBar
MenuComponent
MenuItem
Panel
Point
PopupMenu
Scrollbar
ScrollPane
TextArea
TextComponent
TextField
Toolkit
Window

Java I/O Streams

Java I/O Streams are used for reading or writing information that are on an external source.
Java I/O Streams allow communication between two or more threads.

In Java there are two types of streams:

Byte Streams
Character Streams

Classes that perform input and output operations are stored in the package java.io.
The main classes of java.io package are: File, FileReader, FileWriter, FileInputStream, FileOutputStream, InputStreamReader, OutputStreamWriter, DataInputStream, DataOutputStream, BufferedReader, BufferedWriter, PrintStream, PrintWriter.

Streams example

Example 1

import java.io.*;

public class CreateWriteFile{
    public static void main(String [] args){
        try{
            String filetxt = "Test write file from java.";
            PrintStream output = new PrintStream("myfile1.txt");
            output.println(filetxt);
            output.close();
        }catch(Exception ex){
            System.out.println("Java Error!");
        }
    }
}

Example 2

import java.io.*;

public class CopyString {
   public static void main(String args[]) throws IOException
   {
      FileReader input = null;
      FileWriter output = null;

      try {
         input = new FileReader("input_file.txt");
         output = new FileWriter("output_file.txt");
         
         int s;
         while ((s = input.read()) != -1) {
            output.write(s);
         }
      }catch(Exception ex){
         System.out.println("Java Error!");
      }finally {
         if (input != null) {
            input.close();
         }
         if (output != null) {
            output.close();
         }
      }
   }
}

Java Exceptions

Exceptions in Java represent errors that occur during execution of a program.
Exception handling is used to avoid undesirable display errors, but also easier to correct any errors.

To handle exceptions occurred during runtime uses:
The try-catch-finally
Exception thrown by method throws

Exception example

Try-catch-finally example

public class ExceptionExample{
    public static void main(String [] args){
        try{
            System.out.println("Start");
            int a = Integer.parseInt("123abc");
        }catch(NumberFormatException ex1){
            ex1.printStackTrace();
            System.out.println("Is not numeric!");
        }catch(Exception ex2){
            ex2.printStackTrace();
        }finally{
            System.out.println("End");
        }
    }
}

Throws example

class Exception1 extends Exception {
      public Exception1() {}
}


public class TestException {
    public static void m1() throws Exception1 {
        int a=5;
        if(a>7){
            System.out.println("OK");
        }else{
            System.out.println("Exception a="+a);
            throw new Exception1();        
        }
    }
    public static void main(String[] args) {
        try {
            m1();
        } catch(Exception1 e){
            e.printStackTrace();
        }
    }
}