String Methods

16.2.1 Core Methods You Must Master

Working with strings isn’t just about storing text — it’s about manipulating and analyzing it.
Java’s String class has dozens of built-in methods. The core ones appear in every project:

When does this matter?

• Input validation: Trim spaces, check length, extract parts.

• Parsing: Parse CSV, JSON, query strings.

• Transforming: Change case for usernames or slug URLs.

• Search: Find keywords inside text.

• Replace: Censor bad words, change placeholders, etc.

16.2.2 Mini Lab: Real-World String Processing

Below is an expanded practical Mini Lab with multiple everyday operations.

java
public class StringMethodsMiniLab {
    public static void main(String[] args) {
        String input = "  Hello, Java Web Developer!   ";

        System.out.println("Original: [" + input + "]");
        System.out.println("Length: " + input.length());
        System.out.println("Char at index 7: " + input.charAt(7));
        System.out.println("Substring (7-10): " + input.substring(7, 10));
        System.out.println("Index of 'Java': " + input.indexOf("Java"));
        System.out.println("Uppercase: " + input.toUpperCase());
        System.out.println("Lowercase: " + input.toLowerCase());
        System.out.println("Trimmed: [" + input.trim() + "]");
        System.out.println("Replaced: " + input.replace("Java", "Spring"));

        // Splitting
        String csv = "apple,banana,cherry";
        String[] fruits = csv.split(",");
        for (String fruit : fruits) {
            System.out.println("Fruit: " + fruit.trim());
        }
    }
}

New pieces here:

• split() breaks a string into an array.

• trim() is critical for clean input.

• replace() swaps parts dynamically — e.g., replacing a tech name in a template.

• indexOf() helps you find positions for parsing or highlighting.

✅ Pro tip for real projects:
Never trust user input blindly. Use trim(), toLowerCase(), and replace() to sanitize, normalize, and clean it before saving to a database.