Core Java

Lecture 1: Java Features

This handout is a traditional introduction to any language features. You might not be able to comprehend some of the features fully at this stage but don’t worry, you’ll get to know about these as we move on with the course.

1.1           Design Goals of Java

The massive growth of the Internet and the World-Wide Web leads us to a completely new way of looking at development of software that can run on different platforms like Windows, Linux and Solaris etc.

1.1.1    Right Language, Right Time

•      Java came on the scene in 1995 to immediate popularity.

•      Before that, C and C++ dominated the software development

o compiled, no robust memory model, no garbage collector causes memory leakages, not great support of built in libraries

•      Java brings together a great set of "programmer efficient" features

o   Putting more work on the CPU to make things easier for the programmer.

1.1.2      Java - Buzzwords (Vocabulary)

•      From the original Sun Java whitepaper: "Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high-performance, multi-threaded, and dynamic language."

•      Here are some original java buzzwords.

1.1.3      Java -- Language + Libraries

•      Java has two parts.

o   The core language -- variables, arrays, objects

The Java Virtual Machine (JVM) runs the core language

The core language is simple enough to run on small devices phones, smart cards, PDAs.

o  The libraries

Java includes a large collection of standard library classes to provide "off the shelf" code. (Useful built-in classes that comes with the language to perform basic tasks)

Example of these classes is String, ArrayList, HashMap, StringTokenizer (to break string into substrings), Date ...

Java programmers are more productive in part because they have access to a large set of standard, well documented library classes. 

1.1.4      Simple

•      Very similar C/C++ syntax, operators, etc.

•      The core language is simpler than C++ -- no operator overloading, no pointers, no multiple inheritance

•      The way a java program deals with memory is much simpler than C or C++.

1.1.5      Object-Oriented

•      Java is fundamentally based on the OOP notions of classes and objects.

•      Java uses a formal OOP type system that must be obeyed at compile-time and run-time.

•      This is helpful for larger projects, where the structure helps keep the various parts consistent. Contrast to Perl, which has a more anything-goes feel.

1.1.6      Distributed / Network Oriented

•      Java is network friendly -- both in its portable, threaded nature, and because Common networking operations are built-in to the Java libraries.

1.1.7      Robust / Secure / Safe

•      Java is very robust

o  Both, vs. unintentional errors and vs. malicious code such as viruses.

o   Java has slightly worse performance since it does all this checking. (Or put the other way, C can be faster since it doesn't check anything.)

•      The JVM "verifier" checks the code when it is loaded to verify that it has the correct Structure -- that it does not use an uninitialized pointer, or mix int and pointer types. This is one-time "static" analysis -- checking that the code has the correct structure without running it.

•      The JVM also does "dynamic" checking at runtime for certain operations, such as pointer and array access, to make sure they are touching only the memory they should. You will write code that runs into

•      As a result, many common bugs and security problems (e.g. "buffer overflow") are not possible in java. The checks also make it easier to find many common bugs easy, since they are caught by the runtime checker.

•      You will generally never write code that fails the verifier, since your compiler is smart enough to only generate correct code. You will write code that runs into the runtime checks all the time as you debug -- array out of bounds, null pointer.

•      Java also has a runtime Security Manager can check which operations a particular piece of code is allowed to do. As a result, java can run untrusted code in a "sandbox" where, for example, it can draw to the screen but cannot access the local file system. 

1.1.8      Portable

•      "Write Once Run Anywhere", and for the most part this works.

•      Not even a recompile is required -- a Java executable can work, without change, on any Java enabled platform.

1.1.9      Support for Web and Enterprise Web Applications

•      Java provides an extensive support for the development of web and enterprise applications

•      Servlets, JSP, Applets, JDBC, RMI, EJBs and JSF etc. are some of the Java technologies that can be used for the above mentioned purposes.

1.1.10                       High-performance

•      The first versions of java were pretty slow.

•      Java performance has gotten a lot better with aggressive just-in-time-compiler (JIT) techniques.

•      Java performance is now similar to C -- a little slower in some cases, faster in a few cases. However memory use and startup time are both worse than C.

•      Java performance gets better each year as the JVM gets smarter. This works, because making the JVM smarter does not require any great change to the java language, source code, etc.

1.1.11                       Multi-Threaded

•      Java has a notion of concurrency wired right in to the language itself.

•      This works out more cleanly than languages where concurrency is bolted on after the fact.

1.1.12                       Dynamic

•      Class and type information is kept around at runtime. This enables runtime loading and inspection of code in a very flexible way.

1.1.13                       Java Compiler Structure

•      The source code for each class is in a .java file. Compile each class to produce “.class” file.

•      Sometimes, multiple .class files are packaged together into a .zip or .jar "archive" file.

•      On UNIX or windows, the java compiler is called "javac". To compile all the .java files in a directory use "javac *.java". 

1.1.14 Java: Programmer Efficiency

• Faster Development

o   Building an application in Java takes about 50% less time than in C or C++. So, Faster time to market

o   Java is said to be “Programmer Efficient”.

•      OOP

o   Java is thoroughly OOP language with robust memory system

o   Memory errors largely disappear because of the safe pointers and garbage collector. The lack of memory errors accounts for much of the increased programmer productivity.

•      Libraries

o   Code re-uses at last -- String, ArrayList, Date, available and documented in a standard way

1.1.15 Microsoft vs. Java

•      Microsoft hates Java, since a Java program (portable) is not tied to any particular operating system. If Java is popular, then programs written in Java might promote non-Microsoft operating systems. For basically the same reason, all the non-Microsoft vendors think Java is a great idea.

•      Microsoft's C# is very similar to Java, but with some improvements, and some questionable features added in, and it is not portable in the way Java is. Generally it is considered that C# will be successful in the way that Visual Basic is: a nice tool to build Microsoft only software.

•      Microsoft has used its power to try to derail Java somewhat, but Java remains very popular on its merits.

1.1.16                       Java Is For Real

•      Java has a lot of hype, but much of it is deserved. Java is very well matched for many modern problem

•      Using more memory and CPU time but less programmer time is an increasingly appealing tradeoff.

•      Robustness and portability can be very useful features

•      A general belief is that Java is going to stay here for the next 10-20 years

 Lecture 2: Java Virtual Machine & Runtime Environment

2.1           Basic Concept

When you write a program in C++ it is known as source code. The C++ compiler converts this source code into the machine code of underlying system (e.g. Windows) If you want to run that code on Linux you need to recompile it with a Linux based compiler. Due to the difference in compilers, sometimes you need to modify your code.

Java has introduced the concept of WORA (write once run anywhere). When you write a java program it is known as the source code of java. The java compiler does not compile this source code for any underlying hardware system, rather it compiles it for a software system known as JVM (This compiled code is known as byte code). We have different JVMs for different systems (such as JVM for Windows, JVM for Linux etc). When we run our program the JVM interprets (translates) the compiled program into the language understood by the underlying system. So we write our code once and the JVM runs it everywhere according to the underlying system.

This concept is discussed in detail below 

2.1.1    Byte code

•      Java programs (Source code) are compiled into a form called Java bytecodes.

•      The Java compiler reads Java language source (.java) files, translates the source into Java bytecodes, and places the bytecodes into class (.class) files.

•        The compiler generates one class file for each class contained in java source file.

  

2.1.2      Java Virtual Machine (JVM)

•      The central part of java platform is java virtual machine.

•      Java bytecode executes by special software known as a "virtual machine".

•      Most programming languages compile source code directly into machine code, suitable for execution

•      The difference with Java is that it uses bytecode - a special type of machine code.

The JVM executes Java bytecodes, so Java bytecodes can be thought of as the machine language of the JVM.

  

•      JVM are available for almost all operating systems.

•      Java byte code is executed by using any operating system’s JVM. Thus achieve portability.

2.1.3    Java Runtime Environment (JRE)

•      The Java Virtual Machine is a part of a large system i.e. Java Runtime Environment (JRE).

•      Each operating system and CPU architecture requires different JRE.

•      The JRE consists of set of built-in classes, as well as a JVM.

•      Without an available JRE for a given environment, it is impossible to run Java software.

2.2           Java Program Development and Execution Steps

Java program normally go through five phases. These are

•      Edit,

•      Compile,

•      Load,

•      Verify and

•      Execute

We look over all the above mentioned phases in a bit detail. First consider the following figure that summarizes the all phases of a java program.

2.2.1  Phase 1: Edit

Phase 1 consists of editing a file. This is accomplished with an editor program. The programmer types a java program using the editor like notepad, and make corrections if necessary.

When the programmer specifies that the file in the editor should be saved, the program is stored on a secondary storage device such as a disk. Java program file name ends with a .java extension.

On Windows platform, notepad is a simple and commonly used editor for the beginners. However java integrated development environments (IDEs) such as NetBeans, Borland JBuilder, JCreator and IBM’s Eclipse Java built-in editors that are smoothly integrated into the programming environment.

2.2.2  Phase 2: Compile

In Phase 2, the programmer gives the command javac to compile the program. The java compiler translates the java program into byte codes, which is the language understood by the java interpreter.

To compile a program called Welcome.java type javac Welcome.java at the command window of your system. If the program compiles correctly, a file called Welcome. Class is produced. This is the file containing the byte codes that will be interpreted during the execution phase.

2.2.3 Phase 3: Loading

In phase 3, the program must first be placed in memory before it can be executed. This is done by the class loader, which takes the .class file (or files) containing the byte codes and transfers it to memory. The .class file can be loaded from a disk on your system or over a network (such as your local university or company network or even the internet).

Applications	(Programs)	are loaded into memory and executed using	the	java  interpreter
via the command java. When executing a Java application called Welcome, the command
		Java Welcome
Invokes the	interpreter	for the Welcome application and causes the	class	loader to load

information used in the Welcome program.

2.2.4 Phase 4: Verify

Before the byte codes in an application are executed by the java interpreter, they are verified by the byte code verifier in Phase 4. This ensures that the byte codes for class that are loaded form the internet (referred to as downloaded classes) are valid and that they do not violate Java’s security restrictions. Java enforces strong security because java programs arriving over the network should 

not be able to cause damage to your files and your system (as computer viruses might).

2.2.5 Phase 5: Execute

Finally in phase 5, the computer, under the control of its CPU, interprets the program one byte code at a time. Thus performing the actions specified by the program.Programs may not work on the first try. Each of the preceding phases can fail because of various errors. This would cause the java program to print an error message. The programmer would return to the edit phase, make the necessary corrections and proceed through the remaining phases again to determine if the corrections work properly. 

2.3           Installation and Environment Setting

2.3.1    Installation

•      Download the latest version j2se5.0 (java 2 standard edition) from http://java.sun.com or get it from any other source like CD.

•      Note: j2se also called jdk (java development kit). You can also use the previous versions like jdk 1.4 or 1.3 etc. but it is recommended that you use either jdk1.4 or jdk5.0

•      Install j2se5.0 on your system

Note: For the rest of this handout, assume that j2se is installed in C:\Program Files\Java\jdk1.5.0

2.3.2 Environment Setting

Once you successfully installed the j2se, the next step is environment or path setting. You can accomplish this in either of two ways.

2.3.2.1 Temporary Path Setting

• Open the command prompt from Start   Programs   Accessories    Command Prompt.

The command prompt screen would be opened in front of you.

• Write the command on the command prompt according to the following format

path = < java installation directory\bin >

• So, according to handout, the command will look like this

path = C:\Program Files\Java\jdk1.5.0\bin

• To Test whether path has been set or not, write javac and press ENTER. If the

list of options displayed as shown in the below figure means that you have successfully completed the steps of path setting.

The above procedure is illustrates in the given below picture.

Note: The issue with the temporary path setting is you have to repeat the above explained procedure again and again each time you open a new command prompt window. To avoid this overhead, it is better to set your path permanently

2.3.2.2 Permanent Path Setting

•      In Windows NT (XP, 2000), you can set the permanent environment variable.

•      Right click on my computer icon click on properties as shown below

A System Properties frame would appear as shown in the picture.

• Select  the	advanced  tab  followed  by  clicking  the  Environment  Variable
button. The	Environment variables frame would be displayed in front of you

•      Locate the Path variable in the System or user variables, if it is present there, select it by single click. Press Edit button. The following dialog box would be appeared.

  

• Write; C:\Program Files\Java\jdk1.5.0\bin at the end of the value field. Press OK button. Remember to write semicolon (;) before writing the path for java installation directory as illustrated in the above figure.

•      If Path variable does not exist, click the New button. Write variable name “PATH”, variable value C:\Program Files\Java\jdk1.5.0\bin and press OK button.

•      Now open the command prompt and write javac, press enter button. You see the list of options would be displayed.

•      After setting the path permanently, you have no need to set the path for each new opened command prompt.

2.4              First Program in Java

Like any other programming language, the java programming language is used to create applications. So, we start from building a classical “Hello World” application, which is generally used as the first program for learning any new language.

2.4.1	HelloWorldApp
•	Open notepad editor from Start   ProgarmFiles   Accessories  Notepad.
•	Write the following code into it.

Note: Don’t copy paste the given below code. Probably it gives errors and you can’t able to remove them at the beginning stage.

public class HelloWorldApp

{

public static void main(String args[])

{

System.out.println("Hello World");

}

}

•      To save your program, move to File menu and choose save as option.

• Save your program as “HelloWorldApp.java” in some directory. Make sure to add double quotes around class name while saving your program. For this example create a folder known as “examples” in D: drive

Note: Name of file must match the name of the public class in the file (at line 4). Moreover, it is case sensitive. For example, if your class name is MyClasS, than file name must be MyClasS. Otherwise the Java compiler will refuse to compile the program.

For the rest of this handout, we assume that program is saved in D:\examples directory. 

2.4.2    HelloWorldApp Described

•      Lines 1-3

o   Like in C++, You can add multiple line comments that are ignored by the compiler.

•      Lines 4

o   Line 4 declares the class name as HelloWorldApp. In java, every line of code must reside inside class. This is also the name of our program (HelloWorldApp.java).The compiler creates the HelloWorldApp.class if this program successfully gets compiled.

•      Lines 5

o   Line 5 is where the program execution starts. The java interpreter must find this defined exactly as given or it will refuse to run the program. (However you can change the name of parameter that is passed to main. i.e. you can write String[] argv or String[] someParam instead of String[] args)

o   Other programming languages, notably C++ also use the main() declaration as the starting point for execution. However the main function in C++ is global and resides outside of all classes where as in Java the main function must reside inside a class. In java there are no global variables or functions. The various parts of this main function declaration will be covered at the end of this handout.

•      Lines 6

o   Again like C++, you can also add single line comment

•      Lines 7

o   Line 7 illustrates the method call. The println() method is used to print something on the console. In this example println() method takes a string argument and writes it to the standard output i.e. console.

•      Lines 8-9

o   Line 8-9 of the program, the two braces, close the method main() and the classHelloWorldApp respectively.

2.4.3 Compiling and Running HelloWorldApp

• Open  the  command  prompt  from  Start     Program  Files     Accessories.  OR

alternatively you can write cmd in the run command window.

•      Write cd.. to came out from any folder, and cd [folder name] to move inside the specified directory. To move from one drive to another, use [Drive Letter]: See figure given below

•      After reaching to the folder or directory that contains your source code, in our case HelloWorldApp.java.

•      Use “javac” on the command line to compile the source file ( “.java” file).

D:\examples> javac HelloWorld.java

•      If program gets successfully compiled, it will create a new file in the same directory named HelloWorldApp.class that contains the byte-code.

•      Use “java” on the command line to run the compiled .class file. Note “.class” would be added with the file name.

•      D:\examples> java HelloWorld

•      You can see the Hello World would be printed on the console. Hurrah! You are successful in writing, compiling and executing your first program in java

  

2.4.4    Points to Remember

•      Recompile the class after making any changes

•      Save your program before compilation

•      Only run that class using java command that contains the main method, because program executions always starts form main

2.5           An Idiom Explained

•      You will see the following line of code often:

o   public static void main(String args[]) { …}

•      About main()

o   “main” is the function from which your program starts

o   Why public?

o   Since main method is called by the JVM that is why it is kept public so that it is accessible from outside. Remember private methods are only accessible from within the class

•      Why static?

o   Every Java program starts when the JRE (Java Run Time Environment) calls themain method of that program. If main is not static then the JRE have to create an object of the class in which main method is present and call the main method on that object (In OOP based languages method are called using the name of object if they are not static). It is made static so that the JRE can call it without creating an object.

o   Also to ensure that there is only one copy of the main method per class

•      Why void?

o   Indicates that main ( ) does not return anything.

•      What is String args[] ?

o   Way of specifying input (often called command-line arguments) at startup of application. More on it latter

 Lecture 3: Learning Basics

3.1           Strings

A string is commonly considered to be a sequence of characters stored in memory and accessible as a unit. Strings in java are represented as objects.

3.1.1    String Concatenation

•      “+” operator is used to concatenate strings

o   System.out.println(“Hello” + “World”) will print Hello World on console

•      String concatenated with any other data type such as int will also convert that datatype to String and the result will be a concatenated String displayed on console. For example,

o   int i = 4;

o  int j = 5;

System.out.println (“Hello” + i);// will print Hello 4 on screen

o  However

System.out.println(i+j);//will print 9 on the console because both i and j are of type int.

3.1.2 Comparing Strings

For comparing Strings never use == operator, use equals method of String class.

•      == operator compares addresses (shallow comparison) while equals compares values (deep comparison)

o  E.g. string1.equals(string2)

Example Code: String concatenation and comparison

public class StringTest {

import java.awt.*;

public class AwtSetIconOfFrame{
public static void main(String[] args){
Frame frame = new Frame("Icon setting for the Awt Frame");
Image icon = Toolkit.getDefaultToolkit().getImage("icon_confused.gif");
Label lbl = new Label("Welcome in Roseindia.net Tutorial.",Label.CENTER);
frame.add(lbl);
frame.setSize(400,400);
frame.setIconImage(icon);
frame.setVisible(true);
  }
}

Setting the close button operation for the frame in Java

import java.awt.*;
import java.awt.event.*;

public class AwtCloseButtonEvent{
  public static void main(String[] args){
  Frame frame = new Frame("Close Operation Frame");
  Label lbl = new Label("Welcom in Roseindia.net Tutorial",Label.CENTER);
  frame.add(lbl);
  frame.setSize(400,400);
  frame.setVisible(true);
  frame.addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent we){
  System.exit(0);
  }
  });
  }
}

Making a Frame Non Resizable in Java

import java.awt.*;
import java.awt.event.*;

public class AwtFrameNonResizable{
  public static void main(String[] args){
  Frame frame = new Frame("Non Resizable Frame");
  Image icon = Toolkit.getDefaultToolkit().getImage("icon_confused.gif");
  frame.setIconImage(icon);
  Label lbl = new Label("Welcome in Roseindia.net Tutorial.",Label.CENTER);
  frame.add(lbl);
  frame.setResizable(false);
  frame.setSize(400,400);
  frame.setVisible(true);
  frame.addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent we){
  Frame frame = (Frame)we.getSource();
  frame.dispose();
  }
  });
  }
}

Removing the title bar of the Frame in Java

import java.awt.*;
import java.awt.event.*;

public class AwtWithoutTitleFrame{
public static void main(String[] args){
Frame frame = new Frame("Without Title Bar Frame");
Label lbl = new Label("Welcome in Roseindia.net Tutorial.",Label.CENTER);
frame.setUndecorated(true);
frame.add(lbl);
frame.setSize(400,400);
frame.setVisible(true);
frame.addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent we){
Frame frame = (Frame)we.getSource();
frame.dispose();
  }
  });
  }
}

Create a Container in Java awt

import java.awt.*;
import java.awt.event.*;

public class CreateContainer{
  public static void main(String[] args){
  Panel panel = new Panel();
  panel.add(new Button("Button 1"));
  panel.add(new Button("Button 2"));
  panel.add(new Button("Button 3"));
  Frame frame = new Frame("Container Frame");
  TextArea txtArea = new TextArea();
  frame.add(txtArea, BorderLayout.CENTER);
  frame.add(panel, BorderLayout.SOUTH);
  frame.setSize(400,400);
  frame.setVisible(true);
  frame.addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent we){
  System.exit(0);
  }
  });
  }
}

Changing the Cursor in Java

import java.awt.*;
import java.awt.event.*;

public class ChangeCursor{
  public static void main(String[] args) {
  Frame f = new Frame("Change cursor");
  Panel panel = new Panel();
  Button comp1 = new Button("Ok");
  Button comp2 = new Button("Cancel");
  panel.add(comp1);
  panel.add(comp2);
  f.add(panel,BorderLayout.CENTER);
  f.setSize(200,200);
  f.setVisible(true);
  Cursor cur = comp1.getCursor();
  Cursor cur1 = comp2.getCursor();
  comp1.setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR));
  comp2.setCursor(Cursor.getPredefinedCursor(Cursor.MOVE_CURSOR));
  f.addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent we){
  System.exit(0);
  }
  });

  }
}

Image on Frame in Java AWT

import java.awt.*;
import java.awt.event.*;

public class AwtImage extends Frame{
  Image img;
  public static void main(String[] args){
  AwtImage ai = new AwtImage();
  }

  public AwtImage(){
  super("Image Frame");
  MediaTracker mt = new MediaTracker(this);
  img = Toolkit.getDefaultToolkit().getImage("icon_confused.gif");
  mt.addImage(img,0);
  setSize(400,400);
  setVisible(true);
  addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent we){
  dispose();
  }
  });
  }
  public void update(Graphics g){
  paint(g);
  }
  
  public void paint(Graphics g){
  if(img != null)
  g.drawImage(img, 100, 100, this);
  else
  g.clearRect(0, 0, getSize().width, getSize().height);
  }
}

Event handling in Java AWT

import java.awt.*;
import java.awt.event.*;

public class AwtEvent extends Frame implements ActionListener{
  Label lbl;
  public static void main(String argv[]){
  AwtEvent t = new AwtEvent();
  }
  
  public AwtEvent(){
  super("Event in Java awt");
  setLayout(new BorderLayout());
  try{
  Button button = new Button("INSERT_AN_URL_HERE");
  button.addActionListener(this);
  add(button, BorderLayout.NORTH);
  Button button1 = new Button("INSERT_A_FILENAME_HERE");
  button1.addActionListener(this);
  add(button1, BorderLayout.SOUTH);
  lbl = new Label("Roseindia.net");
  add(lbl, BorderLayout.CENTER);
  addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent we){
  System.exit(0);
  }
  });
  }
  catch (Exception e){}
  setSize(400,400);
  setVisible(true);
  }
  
  public void actionPerformed(ActionEvent e){
  Button bt = (Button)e.getSource();
  String str = bt.getLabel();
  lbl.setText(str);
  }
}

Item Events in Java

import java.awt.*;
import java.awt.event.*;

public class AwtItemEvent extends Frame{
  TextArea txtArea;
  public AwtItemEvent(String title){
  super(title);
  txtArea = new TextArea();
  add(txtArea, BorderLayout.CENTER);
  Choice choice = new Choice();
  choice.addItem("red");
  choice.addItem("green");
  choice.addItem("blue");
  choice.addItemListener(new ItemListener(){
  public void itemStateChanged(ItemEvent e){
  txtArea.setText("This is the " + e.getItem() + " color.\n");
  }
  });
  addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent e){
  System.exit(0);
  }
  });
  add(choice, BorderLayout.NORTH);
  setSize(400,400);
  setVisible(true);
  setResizable(false);
  }
  
  public static void main(String[] args){
  AwtItemEvent f = new AwtItemEvent("AWT Demo");
  }
}

Simple Form in Java

import java.awt.*;
import java.awt.event.*;

public class DataEntry {
  public static void main(String[] args) {
  Frame frm=new Frame("DataEntry frame");
  Label lbl = new Label("Please fill this blank:");
  frm.add(lbl);
  frm.setSize(350,200);
  frm.setVisible(true);
  frm.addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent e){
  System.exit(0);
  }
  });
  Panel p = new Panel();
  Panel p1 = new Panel();
  Label jFirstName = new Label("First Name");
  TextField lFirstName = new TextField(20);
  Label jLastName =new Label("Last Name");
  TextField lLastName=new TextField(20);
  p.setLayout(new GridLayout(3,1));
  p.add(jFirstName);
  p.add(lFirstName);
  p.add(jLastName);
  p.add(lLastName);
  Button Submit=new Button("Submit");
  p.add(Submit);
  p1.add(p);
  frm.add(p1,BorderLayout.NORTH);
  }
}

Item Events in Java

import java.awt.*;
import java.awt.event.*;

public class AwtItemEvent extends Frame{
  TextArea txtArea;
  public AwtItemEvent(String title){
  super(title);
  txtArea = new TextArea();
  add(txtArea, BorderLayout.CENTER);
  Choice choice = new Choice();
  choice.addItem("red");
  choice.addItem("green");
  choice.addItem("blue");
  choice.addItemListener(new ItemListener(){
  public void itemStateChanged(ItemEvent e){
  txtArea.setText("This is the " + e.getItem() + " color.\n");
  }
  });
  addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent e){
  System.exit(0);
  }
  });
  add(choice, BorderLayout.NORTH);
  setSize(400,400);
  setVisible(true);
  setResizable(false);
  }
  
  public static void main(String[] args){
  AwtItemEvent f = new AwtItemEvent("AWT Demo");
  }
}

How to Create Button on Frame

import java.awt.*; 
import java.awt.event.*;
 
public class ButtonText { 
  public static void main(String[] args) {
  Frame frame=new Frame("Button Frame");
  Button button = new Button("Submit"); 
  frame.add(button); 
  frame.setLayout(new FlowLayout());
  frame.setSize(200,100);
  frame.setVisible(true);
  frame.addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent e){
  System.exit(0);
  }
  });
  }
}

How to create CheckBox On frame

import java.awt.*;
import java.awt.event.*;
public class CheckBoxDemo{
  public static void main(String[] args){
  Frame frame= new Frame("Checkbox");
  Checkbox check=new Checkbox("Welcome");
  Checkbox check1=new Checkbox("YOu");
  frame.add(check);
  frame.add(check1);
  frame.setLayout(new FlowLayout());
  frame.setSize(300,200);
  frame.setVisible(true);
  frame.addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent e){
  System.exit(0);
  }
  });
  }
}

Choice Option (Combo) In Java

import java.awt.*;
import java.awt.event.*;
public class ChoiceOptionExample{
  public static void main(String[] args) {
  Frame frame=new Frame("Choice");
  Label label=new Label("What is your Choice:");
  Choice choice=new Choice();
  frame.add(label);
  frame.add(choice);
  choice.add("ROSE");
  choice.add("INDIA");
  choice.add("WELCOME");
  frame.setLayout(new FlowLayout());
  frame.setSize(250,150);
  frame.setVisible(true);
  frame.addWindowListener(new WindowAdapter(){
   public void windowClosing(WindowEvent e){
  System.exit(0);
   }
  });
  }
}

BorderLayout Example In java

import java.awt.*;
import java.awt.event.*;

public class BorderLayoutExample {

  public static void main(String[] args) {
  Frame frame= new Frame("BorderLayout Frame");
  Panel pa= new Panel();
  Button ba1= new Button();
  Button ba2=new Button();
  Button ba3=new Button();
  Button ba4=new Button();
  Button ba5=new Button();
  frame.add(pa);
  pa.setLayout(new BorderLayout());
  pa.add(new Button("Wel"), BorderLayout.NORTH);
  pa.add(new Button("Come"), BorderLayout.SOUTH);
  pa.add(new Button("Rose"), BorderLayout.EAST);
  pa.add(new Button("India"), BorderLayout.WEST);
  pa.add(new Button("RoseIndia"), BorderLayout.CENTER);
  frame.setSize(300,300);
  frame.setVisible(true);
  frame.addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent e){
  System.exit(0);
  }
  });
  }  
}

Radio Button In Java

import java.awt.*;
import java.awt.event.*;
  public class RadioButton{
  public static void main(String[] args) {
  Frame fm=new Frame("RedioButton Group");
  Label la=new Label("What is your choice:");
  fm.setLayout(new GridLayout(0, 1));
  CheckboxGroup cg1=new CheckboxGroup();
  fm.add(la);
  fm.add(new Checkbox("MATH", cg1, true));
  fm.add(new Checkbox("PHYSICS", cg1, false));
  fm.add(new Checkbox("CHEMISTRY", cg1, false));
  fm.add(new Checkbox("ENGLISH", cg1, false));
  fm.setSize(250,200);
  fm.setVisible(true);
  fm.addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent we){
  System.exit(0);
  }
  });
  }
}

TextArea Frame in Java

import java.awt.*;
import java.awt.event.*;

public class TextAreaFrame{
  public static void main(String[] args) {
  Frame frame=new Frame("Text Frame");
  TextArea textArea=new TextArea("Welcome Roseindia",10,20);
  frame.add(textArea);
  frame.setLayout(new FlowLayout());
  frame.setSize(250,250);
  frame.setVisible(true);
  frame.addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent e){
  System.exit(0);
  }
  });
  }
}

Image Demo

import java.awt.*;
import java.awt.event.*;

public class ImageDemo extends Frame{
  Image image;
  public static void main(String[] args) {
  new ImageDemo();
  }
  public ImageDemo(){
  setTitle("Image Demo Example!");
  setSize(300,200);
  addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent we){
  System.exit(0);
  }
  });
  setVisible(true);
  }
  public void paint(Graphics g){
  Toolkit tool = Toolkit.getDefaultToolkit();
  image = tool.getImage("bt_home.gif");
  g.drawString("Image 1:",20,40);
  g.drawImage(image,20,45,this);
  image = tool.getImage("icon_mini_search.gif");
  g.drawString("Image 2:",20,80);
  g.drawImage(image,20,90,this);
  image = tool.getImage("apache_pb2_ani.gif");
  g.drawString("Image 3:",20,130);
  g.drawImage(image,20,150,this);
  }
}

Image Size

import java.awt.*;
import java.awt.event.*;

public class ImageSize extends Frame{
  Image image;
  public static void main(String[] args) {
  try{
  new ImageSize();
  }
  catch(InterruptedException e){}
  }
  public ImageSize() throws InterruptedException{
  Toolkit tool = Toolkit.getDefaultToolkit();
  image = tool.getImage("1.gif");
  MediaTracker mTracker = new MediaTracker(this);
  mTracker.addImage(image,1);
  mTracker.waitForID(1);
  int width = image.getWidth(null);
  int height = image.getHeight(null);
  System.out.println("The width of image: " + width);
  System.out.println("The height of image: " + height);
  setSize(width, height);
  setTitle("Image Size Example!");
  addWindowListener(new WindowAdapter(){
  public void windowClosing(WindowEvent we){
  System.exit(0);
  }
  });
  setVisible(true);
  }
  public void paint(Graphics g){
  g.drawImage(image,0,0,null);
  }
}