Java Programming Language Fundamentals Overview

Sep 13, 2024

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.