String vs StringBuilder in Java

menu_book

Introduction

Strings hold text that does not change often. StringBuilder helps build or change text efficiently without making many copies.

When you have a fixed message or name that won't change.

When you need to add or change text many times, like building a sentence word by word.

When you want your program to run faster while changing text.

When you want to save memory by not creating many copies of text.

When you are working with user input that changes often.

regular_expression

Syntax

Java

String text = "Hello";
StringBuilder builder = new StringBuilder("Hello");

String is simple and easy to use for fixed text.

StringBuilder is better for changing text many times.

emoji_objects

Examples

line_end_arrow_notchThis creates a new String each time you add text, which can be slow if done many times.

Java

String greeting = "Hi";
greeting = greeting + " there!";

line_end_arrow_notchThis changes the same StringBuilder object without making new copies, so it is faster.

Java

StringBuilder builder = new StringBuilder("Hi");
builder.append(" there!");

line_end_arrow_notchUsing StringBuilder to build a greeting step by step.

Java

String name = "Alice";
StringBuilder sb = new StringBuilder();
sb.append("Hello, ").append(name).append("!");

code_blocks

Sample Program

This program shows how String creates a new text when adding, while StringBuilder changes the same object.

Java

public class Main {
    public static void main(String[] args) {
        String text = "Start";
        text = text + " and continue";
        System.out.println("Using String: " + text);

        StringBuilder builder = new StringBuilder("Start");
        builder.append(" and continue");
        System.out.println("Using StringBuilder: " + builder.toString());
    }
}

emoji_objects

Important Notes

line_end_arrow_notch

String objects are immutable, meaning they cannot change once created.

line_end_arrow_notch

StringBuilder is mutable, so it can change without making new objects.

line_end_arrow_notch

Use StringBuilder when you need to change text many times for better speed and memory use.

list_alt_check

Summary

String is good for fixed text that does not change.

StringBuilder is better for building or changing text many times.

Choosing the right one helps your program run faster and use less memory.