📚 Java Reference – Essential Keywords, Methods & Error Handling (2025 Guide)
🧲 Introduction – Why Use a Java Reference?
Whether you’re a beginner or experienced developer, knowing the most-used Java keywords, methods, and error types is essential for writing clean and efficient code. This reference guide helps you quickly understand and recall key elements of the Java language.
🎯 In this article, you’ll explore:
- Reserved Java keywords and their roles
- Must-know methods from Java’s standard libraries
- Input/output handling and exceptions with examples
📌 Topics Covered & Explained
🧱 Java Keywords
Java keywords are reserved words that have a specific meaning in the language. They cannot be used as identifiers (e.g., variable names or method names) and are crucial in defining the structure of Java programs.
public class Example {
private int number;
final double PI = 3.14;
}
📝 Examples: class, public, private, static, final, void, if, try, return, new.
🔤 Java String Methods
Java’s String class provides many methods to manipulate text, such as changing case, finding substrings, checking equality, and more. These methods are essential when handling user input or textual data.
String str = "Java Programming";
System.out.println(str.toUpperCase()); // JAVA PROGRAMMING
System.out.println(str.contains("gram")); // true
System.out.println(str.length()); // 16
➕ Java Math Methods
Java’s Math class offers built-in methods for mathematical calculations like powers, square roots, rounding, and random number generation. These utilities are helpful in any logic-heavy or numerical applications.
System.out.println(Math.max(5, 10)); // 10
System.out.println(Math.sqrt(49)); // 7.0
System.out.println(Math.random() * 100); // Random between 0–100
🖨️ Java Output Methods
Java provides several methods to display output on the console. The System.out.print(), System.out.println(), and System.out.printf() methods are frequently used for debugging and user interaction.
System.out.print("Hello ");
System.out.println("World!");
System.out.printf("Value = %.2f", 3.14159); // Value = 3.14
🧮 Java Arrays Methods
The Arrays class in Java provides static methods to manipulate arrays like sorting, searching, filling, and converting to strings. These utilities are helpful when working with collections of data.
int[] numbers = {5, 2, 8, 1};
Arrays.sort(numbers);
System.out.println(Arrays.toString(numbers)); // [1, 2, 5, 8]
📋 Java ArrayList Methods
ArrayList is a dynamic array that resizes itself as elements are added or removed. Java provides helpful methods like add(), remove(), get(), and contains() for managing items efficiently.
ArrayList<String> list = new ArrayList<>();
list.add("Java");
list.add("Python");
list.remove("Java");
System.out.println(list.contains("Python")); // true
🔗 Java LinkedList Methods
LinkedList is a list that supports fast insertions and deletions. It provides methods like addFirst(), addLast(), and removeFirst() that make it ideal for queue or stack implementations.
LinkedList<String> queue = new LinkedList<>();
queue.addFirst("Start");
queue.addLast("End");
queue.removeFirst(); // removes "Start"
🧠 Java HashMap Methods
HashMap stores data in key-value pairs and provides constant-time performance for basic operations. Methods like put(), get(), containsKey(), and keySet() make it a powerful data structure.
HashMap<String, Integer> map = new HashMap<>();
map.put("A", 1);
map.put("B", 2);
System.out.println(map.get("B")); // 2
System.out.println(map.containsKey("A")); // true
📥 Java Scanner Methods
Scanner is a utility class used to take input from users in a variety of types (String, int, double, etc.). It simplifies interactive console applications and reading files.
Scanner input = new Scanner(System.in);
System.out.print("Enter your name: ");
String name = input.nextLine();
System.out.println("Hello, " + name);
🔁 Java Iterator Methods
Iterators are used to loop over collections safely, especially when you need to remove items while iterating. They provide methods like hasNext(), next(), and remove().
ArrayList<String> list = new ArrayList<>(List.of("A", "B", "C"));
Iterator<String> it = list.iterator();
while (it.hasNext()) {
System.out.println(it.next());
}
❌ Java Errors & Exceptions
Java distinguishes between Errors (serious problems that can’t be handled) and Exceptions (problems that can be caught and fixed). Exceptions are categorized as checked and unchecked.
try {
int result = 10 / 0;
} catch (ArithmeticException e) {
System.out.println("Can't divide by zero.");
}
📝 Common exceptions: NullPointerException, ArrayIndexOutOfBoundsException, IOException, FileNotFoundException.
📌 Summary – Recap & Next Steps
This reference guide covers essential elements of Java that developers use in everyday coding tasks. From keywords to utility methods and exception handling, it’s a quick way to refresh your knowledge.
🔍 Key Takeaways:
- Java keywords define the language syntax and control flow
- String, Math, Array, and Collection methods streamline coding
- Input/output and iterators make your apps interactive and dynamic
- Exceptions improve your program’s reliability
⚙️ Next Steps:
- Practice using these methods in mini projects
- Explore Java Streams, Files, and Concurrency for advanced reference
- Keep this guide bookmarked for daily coding use
❓ Frequently Asked Questions (FAQs)
❓ Can I use all these methods in Java 17 or Java 21?
✅ Yes, all listed methods and keywords are supported in modern Java versions (8+).
❓ What’s the difference between ArrayList and LinkedList?
✅ ArrayList is better for fast random access, while LinkedList is more efficient for insertions/removals.
❓ How can I take multiple inputs using Scanner?
✅ Call .nextLine() repeatedly or use .split() on a single line input to process multiple values.
❓ Are checked and unchecked exceptions handled the same way?
✅ Syntax is similar, but checked exceptions must be declared with throws or caught in a try-catch.
Share Now :
