StringBuffer Introduction

Part of the Logic & Flow section of Coddy's Java journey — lesson 45 of 59.

StringBuffer is similar to StringBuilder but is thread-safe (safe for multiple operations at the same time). It's used to create mutable (modifiable) strings.

Create a StringBuffer with initial text:

StringBuffer sb = new StringBuffer("Hello");

Add more text using append():

sb.append(" World");

After executing the above code, sb contains:

Hello World

Modify text using insert() and replace():

StringBuffer sb = new StringBuffer("Java");
sb.insert(0, "Hi ");       // adds at beginning
sb.replace(0, 2, "Hey");   // replaces "Hi" with "Hey"

After executing the above code, sb contains:

Hey Java

Challenge

Easy

Create a method named modifyText that takes three arguments:

A String (text) to modify
A String (target) to find
A String (replacement) to replace target with

The method should:

Create a StringBuffer with the input text
Replace the first occurrence of target with replacement
Add an exclamation mark at the end
Return the final string

Return messages should be:

If any input is null: return "Invalid input"
If target not found: return original text with exclamation mark
For successful operation: return the modified text

Cheat sheet

StringBuffer is thread-safe and used to create mutable strings.

Create a StringBuffer with initial text:

StringBuffer sb = new StringBuffer("Hello");

Add text using append():

sb.append(" World");

Insert text at a specific position:

sb.insert(0, "Hi ");  // adds at beginning

Replace text using replace():

sb.replace(0, 2, "Hey");  // replaces characters from index 0 to 2

Try it yourself

import java.util.Scanner;

public class Main {
    public static String modifyText(String text, String target, String replacement) {
        // Write your code here
    }
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String text = scanner.nextLine();
        String target = scanner.nextLine();
        String replacement = scanner.nextLine();
        
        if (text.equals("null")) text = null;
        if (target.equals("null")) target = null;
        if (replacement.equals("null")) replacement = null;
        
        System.out.println(modifyText(text, target, replacement));
    }
}