Class notes java

Language Fundamentals
1. Identifiers
2. Reserved words
3. Data types
4. Literals
5. Arrays
6. Types of variabless
7. Var arg method
8. Main method
9. Command line arguments
10. Java coding standards
Identifier: A name in java program is called identifier. It may be class name, method name,
variable name and label name.
Example:




Rules to define java identifiers:
Rule 1: The only allowed characters in java identifiers are:
1) a to z
2) A to Z
3) 0 to 9
4) _
5) $
Rule 2: If we are using any other character we will get compile time error.
Example:
1) total_number-------valid
2) Total#------------------invalid
Rule 3: identifiers are not allowed to starts with digit.
Example:
1) ABC123---------valid
2) 123ABC---------invalid
Rule 4: java identifiers are case sensitive up course java language itself treated as case sensitive
language.



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,Example:
class Test{
int number=10;
int Number=20;
int NUMBER=20; we can differentiate with case.
int NuMbEr=30;
}]
Rule 5: There is no length limit for java identifiers but it is not recommended to take more than
15 lengths.
Rule 6: We can’t use reserved words as identifiers.
Example: int if=10; --------------invalid
Rule 7: All predefined java class names and interface names we use as identifiers.
Example 1:
class Test
{
public static void main(String[] args){
int String=10;
System.out.println(String);
}}
Output:
10
Example 2:
class Test
{
public static void main(String[] args){
int Runnable=10;
System.out.println(Runnable);
}}
Output:
10
Even though it is legal to use class names and interface names as identifiers but it is not a good
programming practice.
Which of the following are valid java identifiers?




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,Reserved words:
• In java some identifiers are reserved to associate some functionality or meaning such
type of reserved identifiers are called reserved words.
Diagram:




Reserved words for data types:
1) byte
2) short
3) int
4) long
5) float
6) double
7) char
8) boolean
Reserved words for flow control:
1) if
2) else
3) switch
4) case
5) default
6) for
7) do


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, 8) while
9) break
10) continue
11) return
Keywords for modifiers:
1) public
2) private
3) protected
4) static
5) final
6) abstract
7) synchronized
8) native
9) strictfp(1.2 version)
10) transient
11) volatile
Keywords for exception handling:
1) try
2) catch
3) finally
4) throw
5) throws
6) assert(1.4 version)
Class related keywords:
1) class
2) package
3) import
4) extends
5) implements
6) interface
Object related keywords:
1) new
2) instanceof
3) super
4) this
Void return type keyword:
• If a method won’t return anything compulsory that method should be declared with the
void return type in java but it is optional in C++.

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