Java Language Fundamentals

Hi guys, here comes the third article in the series of Java articles series. In this article basically we will be talking about basic terminologies in Java Programming language.

To prepare a java application, we need some fundamentals entities provided by the Java Programming Language. They are

1. Tokens
2. Data Types
3. Type Casting
4. Java Statements
5. Arrays

• Tokens
• Smallest logical unit of a program is called as “lexeme”
• The collection of lexeme comes under a particular group called as “Token”
• Example:

 int a = b +c *d;        

• Lexeme: int, a, =, b, +,c,*, d,; —> 9 lexemes are there in above statement.
• Tokens used in above program

1. Data Types: int
2. Identifiers: a,b,c,d
3. Operators: =, + , *
4. Special Symbol: ;

• Types of tokens
• There are 4 types of tokens in java.
• To write a java application, Java has given the following list of tokens

1. Identifiers.
2. Literals
3. Keywords/ Reserved Words
4. Operators

• Identifiers
• Identifier is a name assigned to the programming elements like, variables, methods, classes, abstract classes, interfaces ... etc.
• example:

int a = 10;

int --> Data Type
a ---> variable(identifier)
= --> Operator
10 --> Constant
; --> Terminator        

• To provide identifiers in Java Programming language, there is set of rules & regulations given by Java. they are

1. Identifiers should not be started with any number.
2. Identifiers may be started with an alphabet(a-z or A-Z), ‘_’ symbol, ‘$’ symbol, but subsequent symbols may be a number, alphabet, any symbols etc

• example:

int eno= 101; //valid
int 2eno = 102; // Invalid 
String _eaddr = "Bangalore";// Valid
float $esal = 78000.00f;// Valid 
String emp9no = "E-IN-090" //Valid
String emp_Name = "Dipika" // Valid
float emp2$Sal= 547793.00f // Valid        

1. Identifiers doesn’t allows all the operators & all the special symbols except _ & $

int empNo = 222;//valid
int emp+No = 343;//
String emp*Name = 'dipika' // Invalid
String emp@Bangalore = 'dipika' //Invalid
String emp.Addr = 'Bangalore'// Invalid
String emp_Addr = "Bangalore" // Valid         

1. Identifiers doesn’t allows spaces in between or in the middle of the name.
2. We can’t create duplicate identifiers in the same scope, but we can create duplicate identifiers in different scopes.
3. In java applications, we can use all predefined class names and interface names as identifiers.

class Identifiers{
	public static void main(String[] args){
		int Exception = 10;
		System.out.println("the exception value is:" + Exception);
	}
}
>javac identifiers.java

>java Identifiers
the exception value is:10        

1. Note: Once if we declare “System”[Class Name] as an integer variable then we must use that “System” name as a integer variable only in the remaining of the program.
2. By chance also if we use “System” as a class name then the compiler will raise an error.
3. If we want to use “ System” as class name then we need to use its fully qualified name.

• Fully Qualified Name: Specifying class names and interface names along with package names is called as Fully Qualified Name.

//using any predefined class , variable, methods as a custom identifier
class Custom_Identifier{
	public static void main(String[] args){
		int Exception = 10;
		int System = 20;
		//System.out.println("the exception value is:" + Exception);
		java.lang.System.out.println("The exception value is : " + Exception);
		java.lang.System.out.println("The system value is : " + System);
	}
}        

• Along with the above rules of Identifiers, Java has provided a set of suggestions as well to use identifiers in our java program.

1. In java app, it is suggestible / encouraged to provide identifiers with a particular meaning.

String ppp = "dipika" // not suggested
String name = "dipika" // suggested        

1. In java applications, we don’t have any restrictions over the length of the identifiers, we can declare identifiers with any number of length, but it’s highly recommended to provide length of identifiers about 10 symbols.

String permanentaddresofBangalore = "HSR Layour"// not suggestible/ recommended
String permAddrBlore = "JayaNagar"// recommended 
        

1. If we have multiple words in single identifier, then it is suggestible to separate multiple words, with a special notation like _ symbols.

• Example:

String permAddrBlore = "JayaNagar"// not recommended
String perm_Addr_Blore = "Majestic"// recommended         

• Summary

1. Introduction to Identifiers.
2. Rules of Identifiers
3. Suggestible / Optional rule to create a identifier.

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