Java - String is Immutable (String Buffer & Builder are Mutable)

 You're absolutely right — in Java (and many other languages like Python and C#), strings are immutable, meaning once a String object is created, its value cannot be changed. Here's a deeper look into what that means and why it's important:

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🔒 What Does "Immutable" Mean for Strings?

• No in-place modification: You can't change the characters of a string directly. Any operation that seems to modify a string actually creates a new string object.

  String s = "Hello";
  s = s + " World";  // Creates a new string "Hello World"
  

• Memory efficiency via String Pool: Java uses a String pool to store string literals. When you create a string like "Hello", Java checks the pool first to reuse existing objects, saving memory.

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⚙️ Why Are Strings Immutable?

• Security: Strings are often used in sensitive operations like file paths, network connections, and class loading. Immutability ensures these values can't be changed maliciously.

• Thread safety: Immutable objects are inherently thread-safe since their state can't change after creation.

• Hashing: Strings are commonly used as keys in hash-based collections like HashMap. Immutability ensures the hash code remains consistent.

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🧵 What If You Need Mutable Strings?

Use these classes instead:

Class	Description
StringBuilder	Mutable, not thread-safe. Best for single-threaded scenarios.
StringBuffer	Mutable and thread-safe. Suitable for multi-threaded use.

Example:

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

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