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‎advanced-java/collections/index.md‎

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# Module 1: Arrays
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# Java Collections Framework
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In this module, you'll learn about Arrays in Java.
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The **Java Collections Framework (JCF)** is a set of classes and interfaces that implement commonly used collection data structures. It provides a standard way to handle and organize data in Java, allowing for efficient storage, retrieval, and manipulation of data.
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## Topics Covered:
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- Array Declaration
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- Array Initialization
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- Multi-dimensional Arrays
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## Table of Contents
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1. [Overview](#overview)
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2. [Collection Interfaces](#collection-interfaces)
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3. [Common Implementations](#common-implementations)
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4. [List Interface](#list-interface)
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5. [Set Interface](#set-interface)
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6. [Queue Interface](#queue-interface)
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7. [Map Interface](#map-interface)
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8. [Iterators](#iterators)
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9. [Collections Utility Class](#collections-utility-class)
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10. [Advanced Concepts](#advanced-concepts)
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## Overview
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The **Java Collections Framework** (JCF) includes interfaces, implementations, and algorithms for working with collections of objects. It provides high-level abstractions and implementations for different types of collections such as lists, sets, and maps.
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### Key Components of the Collections Framework:
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- **Interfaces**: Define common behavior for different collection types.
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- **Implementations**: Concrete classes that implement the collection interfaces.
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- **Algorithms**: Methods that operate on collections, such as sorting and searching.
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<br/>
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<div align="center" width=700 height=200>
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<img src="IMAGES/collection.png" class="execution" alt="exception hierarchy">
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</div><br/>
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## Collection Interfaces
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The core interfaces of the Java Collections Framework are:
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- **Collection**: The root interface for all collections. It defines basic operations like adding, removing, and checking for elements.
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- **List**: Extends Collection. It represents an ordered collection that allows duplicates and provides indexed access to elements.
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- **Set**: Extends Collection. It represents a collection of unique elements with no duplicates.
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- **Queue**: Extends Collection. It represents a collection used to hold elements prior to processing.
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- **Deque**: Extends Queue. It represents a double-ended queue where elements can be added or removed from both ends.
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- **Map**: Not a true collection. It represents a collection of key-value pairs, with unique keys.
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## Common Implementations
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- **ArrayList**: Implements the List interface using a dynamic array. Provides fast random access to elements.
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- **LinkedList**: Implements both List and Queue interfaces using a doubly linked list.
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- **HashSet**: Implements the Set interface using a hash table. It provides constant time performance for basic operations.
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- **TreeSet**: Implements Set using a Red-Black tree. It maintains elements in sorted order.
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- **HashMap**: Implements the Map interface using a hash table.
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- **TreeMap**: Implements Map using a Red-Black tree. It maintains keys in sorted order.
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- **PriorityQueue**: Implements Queue using a priority heap. It provides efficient retrieval of the highest-priority element.
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## List Interface
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The **List** interface is an ordered collection that allows duplicate elements. It has several key methods:
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- `add(E e)`: Adds an element to the list.
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- `get(int index)`: Retrieves an element by its index.
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- `remove(int index)`: Removes the element at the specified index.
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- `set(int index, E element)`: Replaces the element at the specified index.
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- `indexOf(Object o)`: Returns the index of the first occurrence of the specified element.
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- `size()`: Returns the size of the list.
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### Common Implementations:
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- **ArrayList**: Provides constant-time random access to elements. It is backed by an array.
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- **LinkedList**: Implements both the List and Queue interfaces. It provides better performance for adding and removing elements at the ends of the list.
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### Example:
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```java
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List<String> list = new ArrayList<>();
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list.add("Apple");
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list.add("Banana");
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list.add("Cherry");
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System.out.println(list.get(0)); // Output: Apple

‎advanced-java/jdbc/index.md‎

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‎advanced-java/jdbcodbc/index.md‎

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# ☕ JDBC Full Guide: Java Database Connectivity (with MySQL)
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---
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JDBC (Java Database Connectivity) is an API that enables Java programs to connect to databases like MySQL, Oracle, PostgreSQL, etc., execute SQL queries, and retrieve results.
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<br/>
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## 📌 JDBC Architecture
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<br/>
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<div align="center" width=700 height=200>
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<img src="IMAGES/jdbcarch.jpg" class="execution" alt="exception hierarchy">
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</div><br/>
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<br/>
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## 🔗 Steps to Connect Java with MySQL Database
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### 1️⃣ Import Packages
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<br/>
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<div class="code-block">
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<pre><code>
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<span class="keyword">import</span> java.sql.Connection<span class="punctuation">;</span>
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<span class="keyword">import</span> java.sql.DriverManager<span class="punctuation">;</span>
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<span class="keyword">import</span> java.sql.ResultSet<span class="punctuation">;</span>
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<span class="keyword">import</span> java.sql.Statement<span class="punctuation">;</span>
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<span class="keyword">import</span> java.sql.PreparedStatement<span class="punctuation">;</span>
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<span class="keyword">import</span> java.sql.SQLException<span class="punctuation">;</span>
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</code></pre>
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</div>
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These are all part of the `java.sql` package.
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<br/>
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### 2️⃣ Register JDBC Driver
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<br/>
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<div class="code-block">
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<pre><code>
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<span class="classname">Class</span><span class="punctuation">.</span><span class="method">forName</span><span class="punctuation">(</span><span class="string">"com.mysql.cj.jdbc.Driver"</span><span class="punctuation">)</span><span class="punctuation">;</span>
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</code></pre>
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</div>
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This loads the MySQL JDBC driver.
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<br/>
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### 3️⃣ Establish Connection
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<br/>
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<div class="code-block">
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<pre><code>
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<span class="keyword">String</span> <span class="variable">url</span> = <span class="string">"jdbc:mysql://localhost:3306/mydatabase"</span><span class="punctuation">;</span> <span class="comment">// 3306 is MySQL default port</span>
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<span class="keyword">String</span> <span class="variable">user</span> = <span class="string">"root"</span><span class="punctuation">;</span>
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<span class="keyword">String</span> <span class="variable">password</span> = <span class="string">"your_password"</span><span class="punctuation">;</span>
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<span class="classname">Connection</span> <span class="variable">conn</span> = <span class="classname">DriverManager</span><span class="punctuation">.</span><span class="method">getConnection</span><span class="punctuation">(</span><span class="variable">url</span>, <span class="variable">user</span>, <span class="variable">password</span><span class="punctuation">)</span><span class="punctuation">;</span>
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</code></pre>
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</div>
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- `localhost`: the host
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- `3306`: the MySQL port
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- `mydatabase`: your database name
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<br/>
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### 4️⃣ Create Statement
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<br/>
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<div class="code-block">
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<pre><code>
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<span class="classname">Statement</span> <span class="variable">stmt</span> = <span class="variable">conn</span><span class="punctuation">.</span><span class="method">createStatement</span><span class="punctuation">();</span>
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</code></pre>
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</div>
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You can also use:
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<div class="code-block">
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<pre><code>
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<span class="classname">PreparedStatement</span> <span class="variable">pstmt</span> = <span class="variable">conn</span><span class="punctuation">.</span><span class="method">prepareStatement</span><span class="punctuation">(</span><span class="string">"INSERT INTO users VALUES (?, ?)"</span><span class="punctuation">);</span>
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</code></pre>
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</div>
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<br/>
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### 5️⃣ Execute Queries
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<br/>
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#### SELECT Example:
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<br/>
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<div class="code-block">
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<pre><code>
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<span class="classname">ResultSet</span> <span class="variable">rs</span> = <span class="variable">stmt</span><span class="punctuation">.</span><span class="method">executeQuery</span><span class="punctuation">(</span><span class="string">"SELECT * FROM users"</span><span class="punctuation">);</span>
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<span class="keyword">while</span> (<span class="variable">rs</span><span class="punctuation">.</span><span class="method">next</span><span class="punctuation">())</span> <span class="punctuation">{</span>
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<span class="method">System.out.println</span><span class="punctuation">(</span><span class="variable">rs</span><span class="punctuation">.</span><span class="method">getString</span><span class="punctuation">(</span><span class="string">"username"</span><span class="punctuation">)</span><span class="punctuation">);</span>
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<span class="punctuation">}</span>
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</code></pre>
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</div>
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#### INSERT Example:
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<br/>
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<div class="code-block">
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<pre><code>
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<span class="keyword">String</span> <span class="variable">query</span> = <span class="string">"INSERT INTO users (username, password) VALUES (?, ?)"</span><span class="punctuation">;</span>
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<span class="classname">PreparedStatement</span> <span class="variable">pstmt</span> = <span class="variable">conn</span><span class="punctuation">.</span><span class="method">prepareStatement</span><span class="punctuation">(</span><span class="variable">query</span><span class="punctuation">)</span><span class="punctuation">;</span>
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<span class="variable">pstmt</span><span class="punctuation">.</span><span class="method">setString</span><span class="punctuation">(</span><span class="number">1</span>, <span class="string">"john"</span><span class="punctuation">)</span><span class="punctuation">;</span>
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<span class="variable">pstmt</span><span class="punctuation">.</span><span class="method">setString</span><span class="punctuation">(</span><span class="number">2</span>, <span class="string">"secret"</span><span class="punctuation">)</span><span class="punctuation">;</span>
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<span class="variable">pstmt</span><span class="punctuation">.</span><span class="method">executeUpdate</span><span class="punctuation">()</span><span class="punctuation">;</span>
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</code></pre>
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</div>
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<br/>
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### 6️⃣ Close Resources
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<br/>
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<div class="code-block">
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<pre><code>
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<span class="variable">rs</span><span class="punctuation">.</span><span class="method">close</span><span class="punctuation">()</span><span class="punctuation">;</span>
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<span class="variable">stmt</span><span class="punctuation">.</span><span class="method">close</span><span class="punctuation">()</span><span class="punctuation">;</span>
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<span class="variable">conn</span><span class="punctuation">.</span><span class="method">close</span><span class="punctuation">()</span><span class="punctuation">;</span>
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</code></pre>
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</div>
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Always close connections to avoid memory leaks.
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<br/>
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## 🧱 JDBC Connection URL Format
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<br/>
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<div class="code-block">
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<pre><code>
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<span class="string">jdbc:mysql://</span><span class="variable">&lt;host&gt;</span><span class="punctuation">:</span><span class="variable">&lt;port&gt;</span><span class="punctuation">/</span><span class="variable">&lt;database&gt;</span><span class="punctuation">?</span><span class="variable">&lt;options&gt;</span>
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</code></pre>
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</div>
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Example:
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<br/>
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<div class="code-block">
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<pre><code>
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<span class="string">jdbc:mysql://</span><span class="variable">localhost</span><span class="punctuation">:</span><span class="number">3306</span><span class="punctuation">/</span><span class="variable">school</span><span class="punctuation">?</span><span class="keyword">useSSL</span><span class="punctuation">=</span><span class="boolean">false</span><span class="punctuation">&amp;</span><span class="keyword">serverTimezone</span><span class="punctuation">=</span><span class="string">UTC</span>
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</code></pre>
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</div>
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<br/>
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## ⚙️ JDBC MySQL Driver Dependency (Maven)
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```xml
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<dependency>
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<groupId>mysql</groupId>
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<artifactId>mysql-connector-java</artifactId>
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<version>8.0.33</version>
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</dependency>
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```
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If using manually, download `mysql-connector-java.jar` and add it to your classpath.
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<br/>
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## 📦 Key JDBC Classes and Interfaces
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<br/>
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| Class / Interface | Purpose |
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|-------------------------|------------------------------------------------|
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| DriverManager | Manages JDBC drivers and connections |
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| Connection | Represents DB connection |
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| Statement | Executes static SQL |
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| PreparedStatement | Executes dynamic SQL with parameters |
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| ResultSet | Holds data from SELECT |
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| SQLException | Handles JDBC exceptions |
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<br/>
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## 🚫 Exception Handling in JDBC
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<br/>
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<div class="code-block">
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<pre><code>
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<span class="keyword">try</span> <span class="punctuation">{</span>
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<span class="comment">// operations</span>
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<span class="keyword">Connection</span> <span class="variable">conn</span> = <span class="method">DriverManager.getConnection</span>(<span class="variable">url</span>, <span class="variable">user</span>, <span class="variable">pass</span><span class="punctuation">);</span>
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<span class="punctuation">}</span> <span class="keyword">catch</span> (<span class="keyword">SQLException</span> <span class="variable">e</span>) <span class="punctuation">{</span>
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<span class="method">e.printStackTrace</span><span class="punctuation">();</span>
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<span class="punctuation">}</span>
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</code></pre>
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</div>
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<br/>
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## 📘 Sample JDBC Program
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<br/>
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<div class="code-block">
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<pre><code>
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<span class="keyword">import</span> <span class="package">java.sql.*;</span>
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<span class="keyword">public</span> <span class="keyword">class</span> <span class="classname">JDBCExample</span> <span class="punctuation">{</span>
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<span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="method">main</span>(<span class="keyword">String</span>[] <span class="variable">args</span>) <span class="punctuation">{</span>
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<span class="keyword">String</span> <span class="variable">url</span> = <span class="string">"jdbc:mysql://localhost:3306/testdb"</span>;
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<span class="keyword">String</span> <span class="variable">user</span> = <span class="string">"root"</span>;
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<span class="keyword">String</span> <span class="variable">password</span> = <span class="string">"password"</span>;
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<span class="keyword">try</span> <span class="punctuation">{</span>
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<span class="keyword">Class</span>.forName(<span class="string">"com.mysql.cj.jdbc.Driver"</span>);
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<span class="keyword">Connection</span> <span class="variable">conn</span> = <span class="method">DriverManager.getConnection</span>(<span class="variable">url</span>, <span class="variable">user</span>, <span class="variable">password</span><span class="punctuation">);</span>
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<span class="keyword">Statement</span> <span class="variable">stmt</span> = <span class="variable">conn</span>.<span class="method">createStatement</span><span class="punctuation">();</span>
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<span class="keyword">ResultSet</span> <span class="variable">rs</span> = <span class="variable">stmt</span>.<span class="method">executeQuery</span>(<span class="string">"SELECT * FROM students"</span>);
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<span class="keyword">while</span> (<span class="variable">rs</span>.<span class="method">next</span>()) <span class="punctuation">{</span>
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<span class="method">System.out.println</span>(<span class="variable">rs</span>.<span class="method">getInt</span>(<span class="string">"id"</span>) + <span class="string">" "</span> + <span class="variable">rs</span>.<span class="method">getString</span>(<span class="string">"name"</span>));
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<span class="punctuation">}</span>
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<span class="variable">rs</span>.<span class="method">close</span><span class="punctuation">();</span>
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<span class="variable">stmt</span>.<span class="method">close</span><span class="punctuation">();</span>
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<span class="variable">conn</span>.<span class="method">close</span><span class="punctuation">();</span>
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<span class="keyword">} catch</span> (<span class="keyword">Exception</span> <span class="variable">e</span>) <span class="punctuation">{</span>
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<span class="method">e.printStackTrace</span><span class="punctuation">();</span>
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<span class="punctuation">}</span>
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<span class="punctuation">}</span>
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<span class="punctuation">}</span>
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</code></pre>
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</div>
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<br/>
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## 🛠️ Common JDBC Ports
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<br/>
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| Database | Default Port |
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|--------------|--------------|
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| MySQL | 3306 |
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| PostgreSQL | 5432 |
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| Oracle DB | 1521 |
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| SQL Server | 1433 |
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## 📎 Tips
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- Always close ResultSet, Statement, and Connection.
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- Use `PreparedStatement` to avoid SQL injection.
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- Use try-with-resources for cleaner code.
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- Handle exceptions gracefully.
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**Happy Coding ☕**

‎core-java/arrays-collections/index.md‎

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</ul>
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<h3>One-Dimensional Arrays</h3>
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<br/>
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<div align="center" width=700 height=200>
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<img src="IMAGES/onedarray.png" class="execution" alt="exception hierarchy">
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</div><br/>
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<p>A one-dimensional array stores a sequence of elements of the same type. It's the simplest type of array in Java.</p>
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<h4>Example of One-Dimensional Array:</h4><br>
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<br>
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<h3>Multi-Dimensional Arrays</h3>
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<br/>
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<div align="center" width=700 height=200>
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<img src="IMAGES/twodarray.jpg" class="execution" alt="exception hierarchy">
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</div><br/>
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<p>Multi-dimensional arrays are arrays of arrays, like a matrix or table of data.</p>
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<h4>Example of Multi-Dimensional Array:</h4><br>

‎index.html‎

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</li>
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<li>
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<a href="#advanced-java/jdbc" onclick="loadContent('advanced-java/jdbc/')"
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>🗄️ JDBC</a
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<a href="#advanced-java/jdbcodbc" onclick="loadContent('advanced-java/jdbcodbc/')"
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>🗄️ JDBC/ODBC</a
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>
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<li>

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