SCJP Language Fundamentals Lecture Notes

Agenda for Language Fundamentals

• Identifiers
• Reserved Words
• Data Types
• Literals
• Arrays
• Types of Variables
• Methods
• Main Method
• Command Line Arguments
• Java Coding Standards

1. Identifiers

• Definition:
  • An identifier is a name used for identification purposes in Java programming.
  • Examples: class names, method names, variable names, and label names.

Example of Identifiers

class Test {  
    public static void main(String[] args) {  
        int x = 10;  
        System.out.println("Hello");  
    }  
}  

• Identifiers in Example:
  • Test (class name)
  • main (method name)
  • String (predefined class name)
  • args (array name)
  • x (variable name)

Rules for Defining Java Identifiers

1. Allowed Characters:
   • Only letters (a-z, A-Z), digits (0-9), dollar sign ($), and underscore (_) are allowed.
   • E.g., total_number is valid but total#number is invalid.
2. Cannot Start with a Digit:
   • Identifiers cannot start with a digit.
   • E.g., 1abc is invalid, while abc1 is valid.
3. Case Sensitivity:
   • Java is case-sensitive. variable and Variable are different identifiers.
4. Length Limit:
   • There is no limit on the length of identifiers, but it is not recommended to use excessively long names for readability.
5. Reserved Words:
   • Cannot use reserved words as identifiers (e.g., if, else, for).
6. Predefined Class Names:
   • Using predefined class names (e.g., String, Runnable) as identifiers is possible but not recommended.

2. Reserved Words

• Definition:
  • Reserved words are specific words in Java that have special meaning and cannot be used as identifiers.
• Total Reserved Words in Java:
  • 53 reserved words
    • Keywords: 50
      • 48 user-defined and 2 unused.
    • Reserved Literals: 3 (true, false, null)

List of Keywords and Reserved Words

• Keywords for Data Types:
  • byte, short, int, long, float, double, boolean, char
• Control Flow Keywords:
  • if, else, switch, case, default, while, do, for, break, continue, return
• Modifiers:
  • public, private, protected, static, final, abstract, synchronized, native, strictfp, transient, volatile
• Exception Handling:
  • try, catch, finally, throw, throws, assert
• Class Related Keywords:
  • class, interface, extends, implements, package, import
• Object Related Keywords:
  • new, instanceof, super, this
• Return Type Keyword:
  • void

Unused Keywords

• List of Unused Keywords:
  • goto, const
  • Reason: They were banned due to issues in other programming languages.

Reserved Literals

• Values:
  • true, false, null
• Purpose:
  • Used to represent boolean values and default value for object references.

3. Important Conclusions

• All reserved words contain only alphabet symbols.
• Java does not have a delete keyword; garbage collection handles object destruction.
• New keywords introduced in Java:
  • strictfp (Java 1.2), assert (Java 1.4), enum (Java 1.5).

Exam Preparation Tips

• Know the 53 reserved words and their classifications.
• Understand rules for defining identifiers.
• Familiarize yourself with keywords related to data types, control flow, modifiers, exception handling, and class-related keywords.