java-tutorial

9) Strings & I/O

Goal

Work with strings safely and do basic file input/output.

Strings

• String is immutable.
• Prefer StringBuilder for repeated concatenation in loops.

var sb = new StringBuilder();
for (int i = 0; i < 3; i++) {
    sb.append(i).append(",");
}
System.out.println(sb);

Files (NIO.2)

Path path = Path.of("notes.txt");
Files.writeString(path, "Hello\n");
String text = Files.readString(path);
System.out.println(text);

Exercises

1. Read a text file and count lines.
2. Given a sentence, count word frequency.
3. Implement isPalindrome(String s) ignoring spaces and case.

Table of contents

1. Getting Started: Install, run, and your first program
2. Java Basics: types, variables, operators, formatting
3. Control Flow: if/switch/loops
4. Methods: parameters, return values, overloading
5. OOP: classes, objects, encapsulation
6. Inheritance & Polymorphism (and when not to use them)
7. Interfaces, abstract classes, and design basics
8. Exceptions and error handling
9. Strings, files, and I/O basics
10. Collections: List/Set/Map and Big-O intuition
11. Generics (the useful parts)
12. Lambdas & Streams
13. Dates and time (java.time)
14. Testing with JUnit 5 (basics)
15. Concurrency: threads, executors, futures
16. JVM basics: memory, GC, performance habits
17. Build tools: Maven essentials (recommended)
18. Next steps: projects to build