Code-Alongs - BD Unit 1 Sprint 1

JavaDoc Documentation

JavaDoc is a documentation generator for Java that extracts comments from Java source code and generates formatted HTML documentation. JavaDoc comments help other developers understand your code's functionality.

JavaDoc Comment Format

/**
 * This is a JavaDoc comment.
 * @param paramName description of the parameter
 * @return description of the return value
 * @throws ExceptionType description of when this exception is thrown
 */

Variables in Java

Variables are used to store data in your programs. In Java, each variable has a specific type that determines what kind of data it can hold.

Variable Declaration and Initialization

• Declaration: type variableName;
• Initialization: variableName = value;
• Declaration and Initialization: type variableName = value;

Java Primitive Data Types

• int - Integers (whole numbers), 32 bits
• double - Double precision floating point numbers, 64 bits
• boolean - true or false values
• char - Single characters like 'A', '*', '7'
• float - Single precision floating point numbers, 32 bits
• long - Integers, 64 bits
• short - Integers, 16 bits
• byte - Integers, 8 bits

Arithmetic Operations

Java supports standard arithmetic operations between numeric values.

Basic Operators

• + - Addition (also used for String concatenation)
• - - Subtraction
• * - Multiplication
• / - Division (be careful with integer division)
• % - Modulus (remainder after division)

Integer vs. Floating Point Division

When you divide two integers, the result is an integer (decimal part is truncated):

int result = 5 / 2;  // result is 2, not 2.5

To get a floating-point result, at least one operand must be a floating-point type:

double result = 5.0 / 2;  // result is 2.5
double result2 = (double) 5 / 2;  // result is 2.5 using casting

Example Code

// Variable declarations
int count = 10;
double price = 29.99;
String name = "Java Programming";

// Arithmetic operations
int sum = count + 5;  // 15
double total = price * count;  // 299.9
int remainder = count % 3;  // 1 (remainder of 10/3)

// String concatenation
String message = "The total price for " + count + " items is $" + total;

Working with Strings in Java

Strings in Java are objects that represent sequences of characters. The String class provides many methods for examining individual characters, comparing strings, searching strings, extracting parts of strings, and creating copies with modified content.

Creating Strings

// String literal
String greeting = "Hello, World!";

// Using the String constructor
String message = new String("Welcome to Java");

Common String Methods

• length() - Returns the number of characters in the string
• charAt(int index) - Returns the character at the specified index
• substring(int beginIndex) - Returns a substring starting from the specified index
• substring(int beginIndex, int endIndex) - Returns a substring between specified indexes
• indexOf(String str) - Returns the index of the first occurrence of the specified substring
• toLowerCase() - Converts all characters to lowercase
• toUpperCase() - Converts all characters to uppercase
• trim() - Removes whitespace from both ends of the string
• replace(char oldChar, char newChar) - Replaces all occurrences of a character
• equals(Object obj) - Compares this string to another object for equality
• equalsIgnoreCase(String anotherString) - Compares strings, ignoring case

String Concatenation

There are several ways to concatenate strings in Java:

// Using + operator
String fullName = firstName + " " + lastName;

// Using concat() method
String result = str1.concat(str2);

// Using StringBuilder (more efficient for many concatenations)
StringBuilder builder = new StringBuilder();
builder.append("Hello");
builder.append(" ");
builder.append("World");
String message = builder.toString();

String Formatting

Java provides powerful string formatting capabilities using the String.format() method:

String formatted = String.format("Hello, %s! You have $%.2f in your account.", name, balance);

// Alternatively, using printf (for printing)
System.out.printf("Hello, %s! You have $%.2f in your account.", name, balance);

Common Format Specifiers

• %s - Formats strings
• %d - Formats decimal integers
• %f - Formats floating-point numbers
• %n - Inserts a platform-specific line separator
• %.2f - Formats a floating-point number with 2 decimal places

Example Code

String message = "Hello, Java Programming!";

// String methods in action
int length = message.length();  // 25
char firstChar = message.charAt(0);  // 'H'
String sub = message.substring(7, 11);  // "Java"
boolean containsJava = message.contains("Java");  // true
String lower = message.toLowerCase();  // "hello, java programming!"
String modified = message.replace('a', 'A');  // "Hello, JAvA ProgrAmming!"

// Finding occurrence
int indexOfJava = message.indexOf("Java");  // 7