Day-84 Understanding String, StringBuffer, and StringBuilder in Java

1. String in Java

• Immutable: Once created, the value of a String object cannot be changed.
• Thread-safety: Since it’s immutable, it is inherently thread-safe.
• Speed: Slower when doing multiple modifications (because each change creates a new object).
• Memory: Stored in String Constant Pool (SCP) if created using literals. Objects created with new go to the heap.

Example:

String str1 = "Hello"; // stored in SCP String str2 = new String("Hello"); // stored in heap 

Here, modifying str1 or str2 will create a new object instead of changing the existing one.

2. StringBuffer in Java

• Mutable: Values can be changed after creation.
• Thread-safe: Methods are synchronized, which makes it safe to use in multi-threaded environments.
• Speed: Slower than StringBuilder due to synchronization.
• Memory: Stored in heap.

Example:

StringBuffer sb = new StringBuffer("Hello"); sb.append(" World"); // modifies the same object System.out.println(sb); // Output: Hello World 

3. StringBuilder in Java

• Mutable: Values can be changed after creation.
• Not thread-safe: Methods are not synchronized, so not safe in multi-threaded environments.
• Speed: Faster than StringBuffer (no synchronization overhead).
• Memory: Stored in heap.

Example:

StringBuilder sb = new StringBuilder("Hello"); sb.append(" World"); System.out.println(sb); // Output: Hello World 

Common Methods in StringBuffer & StringBuilder

Both classes share the same methods. Some useful ones are:

1. append() – Adds text at the end
2. insert() – Inserts text at a position
3. replace() – Replaces part of the text
4. delete() – Deletes part of the text
5. reverse() – Reverses the text
6. charAt(index) – Returns character at given index
7. setCharAt(index, ch) – Sets character at given index
8. length() – Returns current length
9. capacity() – Returns current buffer capacity
10. ensureCapacity(n) – Ensures minimum capacity (increases if needed)

Example:

package stringlearn; public class StringBuilderMethods { public static void main(String[] args) { StringBuilder sb = new StringBuilder("Hello"); // Create a StringBuilder object // 1. append() sb.append(" World"); System.out.println("append: " + sb); // Hello World // 2. insert() sb.insert(5, " Java"); System.out.println("insert: " + sb); // Hello Java World // 3. replace() sb.replace(6, 10, "Python"); System.out.println("replace: " + sb); // Hello Python World // 4. delete() sb.delete(5, 12); System.out.println("delete: " + sb); // Hello World // 5. reverse() sb.reverse(); System.out.println("reverse: " + sb); // dlroW olleH sb.reverse(); // reverse back // 6. charAt() & setCharAt() System.out.println("charAt(1): " + sb.charAt(1)); // e sb.setCharAt(0, 'h'); System.out.println("setCharAt: " + sb); // hello World // 7. length() System.out.println("length: " + sb.length()); // 11 // 8. capacity() & ensureCapacity() System.out.println("capacity: " + sb.capacity()); // default 16 + length sb.ensureCapacity(50); System.out.println("capacity after ensure: " + sb.capacity()); // >= 50 } } 

When to Use What?

Use String

• When you don’t expect modifications
• For constants and small text values

Use StringBuffer

• When working with multi-threaded applications that need thread safety

Use StringBuilder

• When you need fast, efficient string modifications in a single-threaded environment