Java Tutorial
Java is an object oriented programming language, developed by James Gosling at Sun Microsystems and it is released in 1995. Now Oracle Corporation is taking care of java development and the new release is Java 7.
Origin of Java
James Gosling, Mike Sheridan, and Patrik Naughton started to develop a programming language for electronic consumer devices like interactive television. But the attempt was very advanced at that time and it was not successful. Initially the project was known as Oak, later renamed to Green and finally came to Java.
Version
|
Release
|
Codename
|
Changes
|
Comments
|
JDK 1.0
|
January 23, 1996
|
Oak
|
The first stable version – JDK 1.0.2 called Java1
|
|
JDK 1.1
|
February 19, 1997
|
Inner class, Java Beans, JDBC, RMI, reflection which supported Introspection, retooling of AWT
|
||
J2SE 1.2
|
December 8, 1998
|
Playground
|
Strictfp, swing, JIT Compiler, Java Plugin, Java IDL, Collection framework
|
Rebranded to Java 2
|
J2SE 1.3
|
May 8, 2000
|
Kestrel
|
Hotspot JVM, RMI with CORBA, JavaSound, JNDI, JPDA, Synthetic proxy classes.
|
|
J2SE 1.4
|
February 6, 2002
|
Merlin
|
Assert, regular expressions, exception chaining, IPv6 support, Non blocking NIO, logging API, Image IO API, Integrated XML parser and XSLT processor (JAXP), Integrated Security and cryptography extensions, Java Web start, Preferences API
|
First release of the Java platform developed under the Java Community Process.
|
Java 1.5
|
September 30, 2004
|
Tiger
|
Generics, Metadata/Annotations, Autoboxing/Unboxing, Varargs, Enhanced For each loop, Static imports, Automatic Stub generation of RMI objects, Swing-new sin look and feel called Synth, java.util.concurrent, Scanner class
|
Java 5.0
|
Java SE 6
|
December 11, 2006
|
Mustang
|
Scripting language support, Performance improvement, Webservice support through JAX- WS, JDBC 4.0, Java Compiler API,
|
|
Java SE 7
|
July 28, 2011
|
Dolphin
|
JVM Support for dynamic languages, Compressed 64-bit pointers, Strings in switch, automatic resource management in try-statement, simplified varargs method invocation, allowing underscores in numeric literals, SCTP,
|
From Oracle.
|
Software Development Kit
Software development kit or SDK is a set of development tools that allows us for creating software applications or software packages.
Java Development Kit
JDK is Java SDK, it is an extended subset of SDK. This product aimed for java developers to create/run java programs.
Other than Sun (now Oracle) JDK, there are other JDKs commonly available for variety of platforms.
1. GCJ from GNU (GNU Compiler for Java)
2. IBM J9 JDK
3. JRockit
4. Blackdown Java
5. Apple’s Mac OS runtime Java
Along with JDK toolkit, the following features are available
1. Java Development Kit
2. Demos and sample examples
3. Source code
4. Public JRE
5. Java DB
Public JRE is not needed for development purpose. A private JRE is available along with Java development kit.
Java Technology
Java technology is both a programming language and platform.
Java Programming Language: It is a high level language
Java Program
Java program is a set of instructions or human readable character code to do a particular task. This program is storing in a file with a name and .java extension. There are three steps involved for the development of java program.
1. Compose a Java Program
2. Compile the Java program.
3. Run the java class.
Compose a Java Program
Create a file with <filename>.java and write the set of instructions to do a particular task.
Sample ‘Helloworld’ Program
Open a notepad and write the following instructions
class MyClass
{
public static void main(String[] args)
{
System.out.println(“Hello World”);
}
}
Save the file with “MyClass.java”
Each instruction in our program has certain meanings. We will cover all those later.
Compile the Java Program
To compile the above java program, we required a command tool ‘javac’. This javac is available with java development tool kit. Go to the java installation home directory, for example I have installed java into my C:\. Then go to C:\Program Files\Java\jdk1.7.0\bin and we can see ‘javac.exe’.
If we are copying our java program in this bin directory, then we can compile our java program using javac .
Open a command prompt window (Goto Windows Run and type ‘cmd’) and go to the bin directory(cd C:\Program Files\Java\jdk1.7.0\bin)
Then type,
javac MyClass.java
But if we are copying all our java files in bin directory, bin directory will be full of java files. It is not advisable to keep multiple kinds of files in same location. So if we need to compile the java program in user defined locations, we need to set the ‘PATH’ variable.
PATH is an environment variable, specifying a set of directories where executable programs are located.
We can set PATH variable in two ways.
- Setting PATH variable for each user sessions.
Open a command prompt and navigate to the directory where java program is created.
set PATH= C:\Program Files\Java\jdk1.7.0\bin;
- Setting PATH variable globally.
Right click on ‘My Computer’ and select ‘Properties’
Select ‘Advanced’ tab and click on ‘Environment Variables’.
We can see ‘User variables’ and ‘System Variables’.
If PATH variable is available in ‘User Variable’, then edit the PATH variable by adding ‘;’ and add the path (C:\Program Files\Java\jdk1.7.0\bin; ). Otherwise create a new user variable.
Now we can compile a java program from anywhere.
Javac MyClass.java
If the program does not have any errors, command prompt returns. Otherwise it will display all the compilation errors. If any compilation errors, visit the program again, solve the issues and compile again till the command prompt returns without any error.
Run the Java class
After the successful compilation of the java program, check the directory. We can see a new file is generated.
MyClass.class
This is a binary file which contains byte codes. While compiling, the java compiler compiles the java instructions and creates the byte codes. We can run this classfile using ‘java’ command. ‘java’ command is available in the same bin directory (C:\Program Files\Java\jdk1.7.0\bin)
Java MyClass
Output is:
Hello World
Examples
HelloWorld.java
public class HelloWorld {
public static void main(String[] args)
{
System.out.println("Hello World");
}
}
Output
Hello World
HelloToAll.java
public class HelloToAll {
public static void main(String[] args) {
System.out.println("Welcome to the Java World");
System.out.println("I am teaching you Java");
System.out.println("Please practice all the programs");
}
}
Output
Welcome to the Java World
I am teaching you Java
Please practice all the programs
We can incorporate any number of system.out.println statements in a program.
HelloToLiterals.java
public class HelloToLierals
{
public static void main(String[] args)
{
System.out.println("Hello To All");
System.out.println('a');
System.out.println(100);
System.out.println(100.06);
System.out.println(true);
}
}
Output
Hello To All
a
100
100.06
True
Methods.java
public class Methods {
public static void main(String[] args) {
System.out.println("I am a main method. I am going to call test1 method");
test1();
}
public static void test1()
{
System.out.println("I am a method");
}
}
Output
I am a main method. I am going to call test1 method
I am a method
PremitivesAndString.java
public class PremitivesAndString {
static int i;
static byte b;
static float f;
static double d;
static boolean bo;
static short s;
static long l;
static char c;
static String str;
public static void main(String[] args) {
System.out.println("Integer default Value ==> " + i);
System.out.println("Byte default Value ==> " + b);
System.out.println("Float default Value ==> " + f);
System.out.println("Double default Value ==> " + d);
System.out.println("Boolean default Value ==> " + bo);
System.out.println("Short default Value ==> " + s);
System.out.println("Long default Value ==> " + l);
System.out.println("Character default Value ==> " + c);
System.out.println("String default Value ==> " + str);
}
}
Output
Integer default Value ==> 0
Byte default Value ==> 0
Float default Value ==> 0.0
Double default Value ==> 0.0
Boolean default Value ==> false
Short default Value ==> 0
Long default Value ==> 0
Character default Value ==> _
String default Value ==> null
Methodsmany.java
public class MethodsMany {
static int i;
public static void main(String[] args) {
System.out.println("I am a Main Method. I am calling test1() method in many times.");
test1();
test1();
test1();
test1();
System.out.println("I have called test1() method " + i + " Times");
}
public static void test1()
{
System.out.println("I am in a test method");
i++;
}
}
Output
I am a Main Method. I am calling test1() method in many times.
I am in a test method
I am in a test method
I am in a test method
I am in a test method
I have called test1() method 4 Times
Java Programming language – Data Types.
Java programming language is statically typed. Variables must first be declared before they use;
This involves
<Stating the type> <name> = <value>;
Eg: int i=10;
Java programming language supports eight primitive data types.
1. byte
2. short
3. int
4. long
5. float
6. double
7. boolean
8. char
Data Type
|
Default Value
|
Bits
|
Range
|
byte
|
0
|
8 bits
|
-128 to 127
|
short
|
0
|
16 bits
|
-32,768 to 32,767
|
int
|
0
|
32 bits
|
|
long
|
0L
|
64 bits
|
|
float
|
0.0f
|
32 bits
|
|
double
|
0.0d
|
64 bits
|
|
boolean
|
False
|
True and false
|
|
char
|
'\u0000'
|
16 bit
|
'\u0000' to '\uffff' |
Global fields are declared and but not initialized will be set to a reasonable default by the compiler. Generally speaking, the default value will be either zero or null.
Local variables are slightly different. The compiler never assigns a default value to an uninitialized local variable. Accessing an uninitialized local variable will result in a compile time error.
UnInitializedLocalVariable.java
public class UnInitializedLocalVariable {
public static void main(String[] args) {
int i;
System.out.println("I am using i, before initializing " + i);
}
}
Compile time error: The local variable i may not have been initialized.
