Java Syntax Basics

Java Syntax

• Basic Structure of a Java Program

  • Every Java program is defined within a class.
  • The entry point of a program is the main method:

    public static void main(String[] args) {}
    

• Comments

  • Single-line comment: // Comment
  • Multi-line comment: /* Comment */
  • Documentation comment: /** Comment */

• Data Types

  • Primitive Types:
    • int: Integer values (e.g., int number = 10;)
    • double: Floating-point values (e.g., double value = 10.5;)
    • char: Single characters (e.g., char letter = 'A';)
    • boolean: True or false (e.g., boolean isTrue = true;)
  • Reference Types:
    • Objects and arrays.

• Variables

  • Declaration: dataType variableName;
  • Initialization: variableName = value;
  • Combined declaration and initialization: dataType variableName = value;

• Control Flow Statements

  • Conditional Statements:
    • if, else if, else
    • switch statement for multiple conditions.
  • Loops:
    • for loop: for (initialization; condition; increment) {}
    • while loop: while (condition) {}
    • do-while loop: do {} while (condition);

• Operators

  • Arithmetic Operators: +, -, *, /, %
  • Relational Operators: ==, !=, >, <, >=, <=
  • Logical Operators: &&, ||, !
  • Assignment Operators: =, +=, -=, *=, /=, %=

• Arrays

  • Declaration: dataType[] arrayName;
  • Initialization: arrayName = new dataType[size];
  • Accessing elements: arrayName[index]

• Methods

  • Declaration:

    returnType methodName(parameters) {
        // body
    }
    

  • Example:

    public int add(int a, int b) {
        return a + b;
    }
    

• Classes and Objects

  • Class definition:

    class ClassName {
        // fields and methods
    }
    

  • Object creation: ClassName objectName = new ClassName();

• Exception Handling

  • Try-catch block:

    try {
        // code that may cause an exception
    } catch (ExceptionType e) {
        // handle exception
    }
    

• Basic Input/Output

  • Using Scanner for input:

    Scanner scanner = new Scanner(System.in);
    int userInput = scanner.nextInt();
    

  • Printing to console:

    System.out.println("Message");
    

These points cover the fundamental aspects of Java syntax necessary for writing and understanding Java programs.

Basic Structure of a Java Program

• Java programs must be defined within a class structure.
• The program entry point is the main method, which is always formatted as:

  public static void main(String[] args) {}
  

Comments

• Comments can be added to code for explanations and readability.
  • Single-line comments start with //.
  • Multi-line comments are enclosed with /* comment */.
  • Documentation comments begin with /** comment */ and are used for generating documentation.

Data Types

• Java categorizes data types into two main groups: primitive and reference types.

Primitive Types

• int: Represents integer values (e.g., int number = 10;).
• double: Represents floating-point numbers (e.g., double value = 10.5;).
• char: Represents single characters (e.g., char letter = 'A';).
• boolean: Represents truth values, either true or false (e.g., boolean isTrue = true;).

Reference Types

• Reference types include objects and arrays, which hold references to memory locations rather than raw values.

Variables

• Variables must be declared with a specific data type:
  • Declaration syntax: dataType variableName;
  • Initialization syntax: variableName = value;
  • Combined declaration and initialization syntax: dataType variableName = value;

Control Flow Statements

• Control flow statements direct the execution of code based on conditions.

Conditional Statements

• if, else if, and else statements handle decision-making.
• The switch statement allows for evaluating multiple conditions based on the value of a variable.

Loops

• for loop: Utilizes a structure of initialization, condition, and increment for repetition:

  for (initialization; condition; increment) {}
  

• while loop: Repeats code while a specified condition is true:

  while (condition) {}
  

• do-while loop: Executes code at least once before checking the condition:

  do {} while (condition);
  

Operators

• Java uses various operators for calculations and comparisons.

Arithmetic Operators

• Perform mathematical operations: +, -, *, /, % (addition, subtraction, multiplication, division, modulus).

Relational Operators

• Compare values to return boolean results: ==, !=, >, <, >=, <=.