Quick introduction to Java Programming language - Part 1

The first java program to print “Hello Java” as shown below:

public class JavaProgram{
	public static void main(String[]args){
		System.out.println("Hello Java");
	}
}

Now to save the above program, compile and run. The steps given:

• The code is written in notepad as above.
• The file need to save as: JavaProgram.java (program name should be the class name).
• Go to command prompt and go to the directory where the class file saved. Assume it is C:\.
• To compile the code type “javacJavaProgram.java”and click enter. If there are no errors in code, the command prompt will move to the next line.
• To run the compiled code type “java JavaProgram”.
• Now will see the output printed as “Hello Java”.
• Case Sensitivity: Java is case sensitive, which means there is difference between uppercase and lowercase in java.
• Class Name: Do not use any special characters, give a meaning fullname and everyfirst character of a word should be in uppercase.Eg: FirstProgram.java
• Program File Name: The program file should be same as the class name.
• Method Names: Method name first word should start with a Lower Case letter and second word should start with upper case. Eg: public void getArea()
• Public static void main(String args[]):Java should have main() method which is a mandatory to start program execution.

Basic Java Standards/Syntax need to be followed:

• Case Sensitivity: Java is case sensitive, which means there is difference between uppercase and lowercase in java.
• Class Name: Do not use any special characters, give a meaning fullname and everyfirst character of a word should be in uppercase.Eg: FirstProgram.java
• Program File Name: The program file should be same as the class name.
• Method Names: Method name first word should start with a Lower Case letter and second word should start with upper case. Eg: public void getArea()
• Public static void main(String args[]):Java should have main() method which is a mandatory to start program execution.

Identifiers of Java:

Names given by the users/developers to identify a component such as class, variable, method etc. are known as identifiers.

Eg: Class Name: class ShapeOfBox, Method Name: public void getArea(), Variable Name: intboxNumber, intanimal_age;

Points to remember about Identifiers:

• No special characters are allowed.
• Keyword cannot be used as identifiers.

Variables of Java:

It is a temporary space in a memory which is used to store the value. Types of variables are:

1. Variables declared within a method are known as Local variables. It must be initialized before using it.

2. Variables declared inside the class (not in-side the method) are known as Global variables/Class variables.

3. Variables declared at the creation of object instance are known as Instance variables. Literals of Java: Some user data are known as Literals. Eg. System.out.println (“Hello Java”); “Hello Java” is literals here.

Literals of Java:

Some user data are known as Literals. Eg. System.out.println ("Hello Java"); "Hello Java" is literals here.

Java Comments:

It is a non-executable statement. Eg: //Login details à(Single line comment operator), /*--------*/ à(Multiline comment operator)   

public class JavaProgram{

    /* This is a java program.
     * This will print 'Hello Java' as the output
     * This is also an example multiline comment block
     */

  public static void main(String[]args){
     // This is a single line comment
     /* This is also a single line comment. */
      System.out.println("Hello Java");
  }
}

Keywords of Java:

These are pre-defined words, each keyword has specific meaning. All keywords are in lower case.

The Java Keywords are:

Java Operators:        

Symbols used for some specific operations are called operators.

Eg: +, -, *, / etc

Java Modifiers:

It is used to modify classes, methods, etc.

Types of modifiers:

• Access Modifiers: public, default, protected, private
• Non-access Modifiers: final, abstract