Java StringBuilder and StringBuffer

The core point of `StringBuilder` and `StringBuffer` in Java is to provide mutable (modifiable) sequences of characters. This contrasts sharply with `String` objects, which are immutable (their values cannot be changed after creation).

Here’s a breakdown of why this is important and what problems they solve:

1. Problem with `String` Immutability for Modifications: When you perform operations that seem to modify a `String`, like concatenation (`+` or `concat()`), you’re not actually changing the original `String`. Instead, a new `String` object is created in memory with the modified content.

   ```java String s = “Hello”; s = s + " World"; / “Hello” is discarded (eligible for GC), / s now points to a new String “Hello World” s = s + “!”; / “Hello World” is discarded, / s now points to a new String “Hello World!” ``` In a loop or when performing many modifications, this creates many intermediate `String` objects. This can lead to:

   • Performance Overhead: Creating new objects is relatively expensive.
   • Increased Garbage Collection: More objects mean more work for the garbage collector, which can pause your application.

2. Solution: `StringBuilder` and `StringBuffer` (Mutable Strings): These classes allow you to modify the character sequence directly within the same object, without creating new objects for each modification.

   ```java / Using StringBuilder StringBuilder sb = new StringBuilder(“Hello”); sb.append(" World"); / Modifies the internal buffer of sb sb.append("!"); / Modifies the internal buffer of sb again String result = sb.toString(); / Only one new String object created at the end ```

   This is much more efficient for situations where you’re building or modifying strings dynamically.

Key Differences and When to Use Which:

Feature	`String`	`StringBuilder` (Java 5+)	`StringBuffer` (Java 1.0)
Mutability	Immutable	Mutable	Mutable
Thread-Safety	Inherently thread-safe (due to immutability)	Not thread-safe (faster)	Thread-safe (synchronized methods, slower)
Performance	Poor for many modifications	Excellent for single-threaded modifications	Good, but slower than `StringBuilder` due to sync

When to use `String`:

1. For fixed string values that won’t change.
2. When you need immutability (e.g., for keys in a `HashMap`, for constants).
3. For a small, fixed number of concatenations (the Java compiler often optimizes simple concatenations using `StringBuilder` behind the scenes anyway, e.g., `String x = “a” + “b” + “c”;`).

When to use `StringBuilder`:

1. This is the generally recommended choice for most string manipulation tasks where the string is built or modified in a single thread.
2. Building strings in loops.
3. Complex string formatting or construction.
4. When performance for string modification is critical in a single-threaded environment.

When to use `StringBuffer`:

1. When you need a mutable string that will be accessed and modified by multiple threads concurrently. The `synchronized` methods ensure that operations are atomic and prevent race conditions.
2. In older codebases predating Java 5.
3. However, even in multi-threaded scenarios, `StringBuilder` is often preferred if synchronization can be handled externally (e.g., by synchronizing the block of code that uses the `StringBuilder`), or if concurrent data structures (like `ConcurrentLinkedQueue` for building strings from multiple threads) are more appropriate.

In summary:

1. Use `String` for immutable, fixed text.
2. Use `StringBuilder` for efficient, mutable string operations in single-threaded contexts (most common use case).
3. Use `StringBuffer` only when you explicitly need thread-safe mutable string operations, understanding the slight performance cost.

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Problem with String in Java

One of its biggest strength “immutability” is a biggest problem of Java String if not used correctly. many a times we create a String and then perform a lot of operation on them e.g. converting string into uppercase, lowercase , getting substring out of it , concatenating with other string etc. Since String is an immutable class every time a new String is created and older one is discarded which creates lots of temporary garbage in heap. If String are created using String literal they remain in String pool. To resolve this problem Java provides us two Classes StringBuffer and StringBuilder. String Buffer is an older class but StringBuilder is relatively new and added in JDK 5.

Differences between String and StringBuffer in Java

Main difference between String and StringBuffer is String is immutable while StringBuffer is mutable means you can modify a StringBuffer object once you created it without creating any new object. This mutable property makes StringBuffer an ideal choice for dealing with Strings in Java. You can convert a StringBuffer into String by its toString() method.

Difference between StringBuilder and StringBuffer

StringBuffer is very good with mutable String but it has one disadvantage all its public methods are synchronized which makes it thread-safe but same time slow. In JDK 5 they provided similar class called StringBuilder in Java which is a copy of StringBuffer but without synchronization. Try to use StringBuilder whenever possible it performs better in most of cases than StringBuffer class. You can also use “” for concatenating two string because “” operation is internal implemented using either StringBuffer or StringBuilder in Java. If you see StringBuilder vs StringBuffer you will find that they are exactly similar and all API methods applicable to StringBuffer are also applicable to StringBuilder in Java. On the other hand String vs StringBuffer is completely different and there API is also completely different, same is true for StringBuilders vs String.

String Buffer

A thread-safe, mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls. (String is immutable)

String Builder

A mutable sequence of characters. This class provides an API compatible with StringBuffer, but with no guarantee of synchronization. This class is designed for use as a drop-in replacement forStringBuffer in places where the string buffer was being used by a single thread (as is generally the case). Where possible, it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations.

Differences between String, StringBuffer and StringBuilder in Java

Before looking difference between String and StringBuffer or StringBuilder let’s see some fundamental properties of String Class in Java.

1. String is immutable in Java: String is by design immutable in java you can check this post for reason.

Immutability offers lot of benefit to the String class e.g. his hash code value can be cached which makes it a faster hashmap key; it can be safely shared between multithreaded applications without any extra synchronization. To know why strings are immutable in java see the link 2)when we represent string in double quotes like “abcd” they are referred as String literal and String literals are created in String pools.

1. “” operator is overloaded for String and used to concatenated two string. Internally “” operation is

implemented using either StringBuffer or StringBuilder.

1. Strings are backed up by Character Array and represented in UTF-16 format.
2. String class overrides equals() and hashcode() method and two Strings are considered to be equal if

they contain exactly same character in same order and in same case. If you want ignore case comparison of two strings consider using equalsIgnoreCase() method. To learn how to correctly override equals method in Java see the link.

1. toString() method provides string representation of any object and its declared in Object class and its

recommended for other class to implement this and provide string representation.

1. String is represented using UTF-16 format in Java.
2. In Java you can create String from byte array, char array, another string, from StringBuffer or from

StringBuilder. Java String class provides constructor for all of these.