Breaking Down the Differences Between String Buffer and String Builder
Strings are one of the most fundamental components in Java programming. They represent sequences of characters used to store text data such as names, addresses, identifiers, or even numerical values represented as text. Strings are widely used in almost every Java application because they allow programmers to handle text efficiently. Whether it is user input, file I/O, or displaying messages, strings play an essential role.
Immutable Nature of Strings
The String class in Java is unique because it creates immutable objects. Immutability means that once a string object is created, its content cannot be changed. For example, if you create a string with the value «apple,» you cannot modify this string to become «applepie» without creating a new string object. When you modify a string, a completely new object is generated with the updated value, and the original string remains unchanged.
This immutable property provides benefits such as thread safety and security. However, it also leads to performance issues when strings are manipulated frequently, as creating new string objects consumes more memory and CPU time.
Why Mutability Matters
In programming, there are scenarios where strings need to be changed often, such as building dynamic text, concatenating strings in loops, or modifying text content repeatedly. In such cases, immutable strings become inefficient because every change produces a new string object.
To overcome this, Java introduced mutable alternatives that allow strings to be changed without creating new objects every time. These mutable string classes are StringBuffer and StringBuilder.
What Is a StringBuffer?
StringBuffer is a mutable sequence of characters. Unlike the immutable String class, StringBuffer objects can be modified after they are created. This means you can append, insert, or delete characters from a StringBuffer object without creating new objects.
Thread Safety and Synchronization
One of the key features of StringBuffer is that it is thread-safe. This means multiple threads can safely use the same StringBuffer instance without causing data inconsistency or corruption. StringBuffer achieves thread safety through synchronization, ensuring that only one thread can access methods of the object at a time.
Synchronization adds a layer of safety in multi-threaded environments but comes at the cost of performance. Because threads have to wait for each other to finish accessing the StringBuffer, operations on it are slower compared to non-synchronized alternatives.
Characteristics of StringBuffer
StringBuffer has an internal character array stored on the heap, which holds the sequence of characters. This array can expand dynamically as more characters are added. Methods like append(), insert(), and delete() modify the content directly in this array.
Common Usage of StringBuffer
StringBuffer is especially useful in applications where strings are modified by multiple threads simultaneously, such as in server-side programming or concurrent applications. Its synchronization guarantees data consistency but may cause delays due to thread contention.
What Is a StringBuilder?
StringBuilder is similar to StringBuffer in that it provides a mutable sequence of characters. It allows for the efficient modification of strings without creating new objects. StringBuilder was introduced later than StringBuffer, starting with Java 5, as an alternative optimized for single-threaded scenarios.
Lack of Thread Safety in StringBuilder
Unlike StringBuffer, StringBuilder is not synchronized. This means it does not provide thread safety, and it should only be used in contexts where only one thread accesses the object at a time.
Because StringBuilder does not have the overhead of synchronization, it performs faster than StringBuffer, making it the preferred choice for string manipulation in single-threaded environments.
Usage Scenarios for StringBuilder
StringBuilder is ideal for situations where strings need to be constructed or modified frequently in a single thread, such as in desktop applications, utility programs, or any performance-critical code that does not require thread safety.
Comparing StringBuffer and StringBuilder
Both StringBuffer and StringBuilder:
- They are mutable, allowing modification of string content.
- Store characters in a dynamically resizable array on the heap.
- Provide similar APIs with methods like append(), insert(), delete(), and reverse().
- Improve performance compared to using immutable String objects for repeated modifications.
Differences in Synchronization and Performance
The primary difference lies in synchronization:
- StringBuffer methods are synchronized, ensuring thread safety but slower performance.
- StringBuilder methods are not synchronized, offering faster performance but no thread safety.
This difference means that developers must choose between safety and speed based on their specific application requirements.
Memory and Usage Considerations
Both classes store data on the heap and manage their capacity dynamically. The choice between them impacts memory access speed and concurrency control.
StringBuffer Internal Working
StringBuffer internally maintains a character array to store the string data. When a StringBuffer object is created, an initial capacity for this array is set, typically 16 characters by default if no initial size is specified. This capacity refers to the size of the array allocated, not the length of the string currently stored. As more characters are added using methods like append() or insert(), the array dynamically grows to accommodate the new data.
When the capacity is exceeded, the array size is automatically increased by creating a new, larger array and copying the existing characters into it. This resizing operation usually doubles the previous capacity and adds two additional characters. This behavior helps reduce the number of times resizing is needed, improving performance when the buffer size grows gradually.
The dynamic resizing mechanism means StringBuffer efficiently manages memory without frequent reallocation on every addition of characters, unlike immutable String objects that create new objects for every modification.
Synchronization Mechanism in StringBuffer
The thread safety of StringBuffer is ensured by synchronizing its methods. Synchronization is a process that prevents multiple threads from accessing critical sections of code simultaneously, thereby avoiding data corruption and inconsistencies.
Every method that modifies the content of a StringBuffer, such as append(), insert(), delete(), and replace(, is synchronized. When one thread is executing any of these methods on a StringBuffer instance, other threads that try to invoke synchronized methods on the same object must wait until the first thread completes its execution.
This exclusive access guarantees that the internal state of the StringBuffer remains consistent even in concurrent environments, but it introduces overhead in the form of locking and unlocking mechanisms. Consequently, operations become slower, especially under high contention scenarios where many threads attempt to modify the same StringBuffer.
Common Methods and Usage of StringBuffer
StringBuffer provides a rich set of methods to manipulate string content efficiently. Some of the most frequently used methods include:
- Append (): Adds the specified string or other data types (like int, char, boolean) to the end of the existing sequence.
Insert t(): Inserts the specified string or character at a given index.
Delete e(): Removes a portion of the sequence between specified indices. - Replace (): Replaces a specified range with a new string.
- Reverse (): Reverses the characters in the sequence.
- Capacity (): Returns the current capacity of the buffer.
Length h(): Returns the current length of the character sequence. - toString(): Converts the StringBuffer content to a regular immutable String.
Example usage:
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StringBuffer buffer = new StringBuffer(«Hello»);
buffer.append(» World»);
buffer.insert(5, «,»);
System.out.println(buffer.toString()); // Outputs: Hello, World
This demonstrates how the buffer can be modified dynamically without creating new objects.
When to Use StringBuffer
StringBuffer is preferred in multi-threaded applications where multiple threads might access and modify the same mutable string. Its synchronized methods ensure safe operation without risking race conditions or inconsistent data. Examples include:
- Logging frameworks where log messages are built by different threads.
- Server applications handling multiple concurrent requests that update shared string data.
- Situations where thread-safe string manipulation is critical.
However, if thread safety is not required, the overhead of synchronization makes StringBuffer less efficient compared to alternatives.
Exploring StringBuilder
StringBuilder’s Internal Architecture
Like StringBuffer, StringBuilder internally uses a resizable character array stored on the heap. It also starts with a default capacity (16 characters) unless specified otherwise. The buffer automatically resizes itself when needed using the same doubling strategy applied by StringBuffer.
This internal implementation allows StringBuilder to perform string modifications quickly by manipulating the character array directly rather than creating new immutable string objects.
Lack of Synchronization and Its Impact
The primary difference between StringBuilder and StringBuffer is that StringBuilder does not synchronize its methods. It is designed to be used in single-threaded contexts or when external synchronization is managed by the developer.
By eliminating synchronization, StringBuilder removes the locking overhead, significantly improving performance. This makes it especially suitable for applications where string manipulation occurs in a single thread, such as:
- String concatenations inside loops.
- Building strings in local variables.
- Temporary string manipulations where concurrency is not an issue.
However, because it is not thread-safe, using StringBuilder in a multi-threaded environment without proper synchronization can lead to unpredictable behavior and corrupted data.
Key Methods Provided by StringBuilder
StringBuilder offers the same API as StringBuffer, including methods like append(), insert(), delete(), replace(), reverse(), capacity(), length(), and toString(). These methods work identically, except that they do not have synchronized implementations.
Example:
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StringBuilder builder = new StringBuilder(«Good»);
builder.append(» Morning»);
builder.insert(4, «,»);
System.out.println(builder.toString()); // Outputs: Good, Morning
This shows how StringBuilder allows easy and efficient modification of strings.
When to Use StringBuilder
StringBuilder should be chosen over StringBuffer when:
- The application is single-threaded.
- Performance is a priority, and thread safety is not a concern.
- The mutable string operations are frequent and need to be fast.
It is commonly used in scenarios like:
- Local string manipulation in methods.
- Temporary construction of strings before returning them.
- Performance-critical code where the overhead of synchronization is undesirable.
Why Performance Matters in String Operations
String manipulation is a common operation in most software applications. Efficient string handling can drastically affect the overall performance of a program, especially when dealing with large datasets or intensive text processing.
Repeatedly creating new immutable String objects can cause significant overhead in terms of memory and CPU usage. Mutable string classes like StringBuffer and StringBuilder help reduce this overhead by modifying strings in place.
Benchmarking StringBuffer vs StringBuilder
Performance benchmarks consistently show that StringBuilder outperforms StringBuffer when used in single-threaded environments. The main reason is the absence of synchronization in StringBuilder, which removes the overhead caused by locking.
In tests where large numbers of append operations are performed, StringBuilder executes faster due to its lightweight implementation. StringBuffer, on the other hand, incurs additional CPU cycles managing thread safety, resulting in slower performance.
For example, if a program appends thousands of strings in a loop, using StringBuilder can cut down execution time significantly compared to StringBuffer.
Practical Performance Example
Consider the following code snippet measuring append performance:
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long startTime = System.currentTimeMillis();
StringBuilder builder = new StringBuilder();
for (int i = 0; i < 100000; i++) {
builder.append(i);
}
long endTime = System.currentTimeMillis();
System.out.println(«StringBuilder time: » + (endTime — startTime) + » ms»);
startTime = System.currentTimeMillis();
StringBuffer buffer = new StringBuffer();
for (int i = 0; i < 100000; i++) {
buffer.append(i);
}
endTime = System.currentTimeMillis();
System.out.println(«StringBuffer time: » + (endTime — startTime) + » ms»);
Typically, the StringBuilder version will complete faster than the StringBuffer version by a significant margin.
Trade-offs Between Safety and Speed
Choosing between StringBuffer and StringBuilder is a trade-off between thread safety and speed. If multiple threads need to manipulate the same mutable string, StringBuffer is the safe choice. If the operations occur in a single thread or are externally synchronized, StringBuilder provides better performance.
Developers must evaluate their application’s concurrency requirements and decide accordingly.
Converting Between StringBuffer and StringBuilder
Why Conversion Might Be Needed
Sometimes legacy code or libraries use StringBuffer, while newer code prefers StringBuilder for performance reasons. In such cases, conversion between these types can be necessary.
Direct conversion is not possible since they are distinct classes. However, both provide methods to convert to the immutable String class, which can be used as an intermediary.
Converting StringBuffer to StringBuilder
The process involves two steps:
- Convert the StringBuffer to a String using the toString() method.
- Use the String constructor of StringBuilder to create a new StringBuilder instance.
Example:
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StringBuffer buffer = new StringBuffer(«Example»);
String str = buffer.toString();
StringBuilder builder = new StringBuilder(str);
This effectively transfers the content from a thread-safe buffer to a faster, non-synchronized builder.
Converting StringBuilder to StringBuffer
The reverse conversion is similar:
- Convert StringBuilder to String using toString().
- Initialize a new StringBuffer with the string.
Example:
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StringBuilder builder = new StringBuilder(«Example»);
String str = builder.toString();
StringBuffer buffer = new StringBuffer(str);
This allows legacy or synchronized code to work with data produced by StringBuilder.
Considerations When Converting
Conversion involves creating intermediate String objects, which can have minor performance costs. Therefore, such conversions should be done sparingly, ideally only when necessary.
Internal Character Array Allocation
Both StringBuffer and StringBuilder internally maintain a character array to hold the current sequence of characters. This array acts as the underlying storage for the mutable string.
When an instance is created, the default initial capacity is typically 16 characters unless a specific capacity is provided during instantiation. This capacity is not the same as the current length of the stored characters but rather the size of the allocated character array.
The advantage of this pre-allocation is to reduce the number of times the array needs to be resized and copied when new characters are appended or inserted.
Dynamic Expansion of Capacity
When the internal character array is full and more characters need to be added, both classes automatically increase their capacity to accommodate the additional data.
The algorithm for capacity increase is:
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newCapacity = (oldCapacity * 2) + 2
This strategy of doubling plus two helps balance between reducing the frequency of resizing operations and avoiding excessive memory allocation.
For example, if the initial capacity is 16, the first expansion will allocate 34 characters, then 70, and so forth.
Memory Impact of Resizing
Resizing involves creating a new, larger array and copying the existing characters to it. This copying operation has a cost in terms of time and CPU resources.
Thus, frequent expansions during large or unpredictable string concatenations can degrade performance. To mitigate this, developers can:
- Provide an initial capacity estimate when constructing StringBuffer or StringBuilder.
- Avoid extremely frequent resizing by batching append operations where possible.
Garbage Collection and Object Lifecycle
Unlike immutable Strings, which create new objects on every modification, StringBuffer and StringBuilder reuse their internal character array as much as possible.
However, when resizing occurs, the old array becomes eligible for garbage collection once replaced by the new one. This creates some transient memory overhead but is generally less costly than creating new String objects repeatedly.
Since these classes reside on the heap, their lifetime depends on references held by the program. Proper management of references ensures timely garbage collection.
Thread Safety in Detail
Synchronization Fundamentals
StringBuffer achieves thread safety by synchronizing its methods. Synchronization is a concurrency control mechanism that restricts access to critical sections of code so that only one thread can execute them at a time.
In Java, synchronization is implemented using monitors (locks) associated with objects. When a thread enters a synchronized method, it acquires the object’s lock. Other threads attempting to enter synchronized methods on the same object will block until the lock is released.
Method-Level Synchronization in StringBuffer
Every mutating method in StringBuffer is synchronized. For example:
- append()
- insert()
- delete()
- replace()
This guarantees that concurrent modifications do not corrupt the internal character array.
Example:
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public synchronized StringBuffer append(String str) {
// method implementation
}
This forces any thread calling append() to wait if another thread is already inside any synchronized method on the same StringBuffer object.
Performance Cost of Synchronization
Synchronization adds overhead because:
- Threads may block and wait, causing delays.
- Lock acquisition and release consume CPU cycles.
- Context switches between threads add latency.
Therefore, while synchronization is essential for thread safety, it reduces throughput and increases latency compared to non-synchronized alternatives.
StringBuilder’s Lack of Synchronization
In contrast, StringBuilder methods are not synchronized. They can be accessed and modified by multiple threads simultaneously, which leads to race conditions and unpredictable behavior if used without proper external synchronization.
Using StringBuilder in multi-threaded contexts requires careful coordination by the programmer, often through explicit synchronization blocks or other concurrency utilities.
StringBuffer Usage Scenarios
StringBuffer is appropriate when:
- Multiple threads need to modify the same mutable string.
- Built-in thread safety is required without additional synchronization.
- Legacy applications written before Java 5 continue to use StringBuffer.
Example: In a multi-threaded web server, multiple threads may log messages by appending to a shared log buffer. StringBuffer ensures that log entries are not interleaved or corrupted.
StringBuilder Usage Scenarios
StringBuilder is better suited when:
- Only a single thread is responsible for building or modifying the string.
- High performance is required with minimal overhead.
- String concatenation occurs within local variables or method scopes.
Example: Constructing a SQL query string inside a method, where the string is not shared across threads.
Hybrid Approaches
Sometimes, a hybrid approach can be used where a StringBuilder is used locally for fast string construction, then its result is passed safely to a shared StringBuffer if needed.
Core Methods of StringBuffer and StringBuilder
Both classes share almost identical APIs, making it easy to switch between them.
- Append (String s): Adds a string to the end.
Insert t(int offset, String s): Inserts a string at the specified position. Delete te(int start, int end): Removes characters from start to end. - replace(int start, int end, String s): Replaces characters from start to end.
- Reverse (): Reverses the character sequence.
- Capacity (): Returns the current buffer capacity.
Length h(): Returns the current length of the sequence. - setLength(int newLength): Sets the length of the sequence.
- toString(): Converts to an immutable String object.
Example Demonstrating Common Methods
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StringBuffer buffer = new StringBuffer(«Hello»);
buffer.append(» World»);
buffer.insert(5, «,»);
buffer.replace(6, 11, «Java»);
buffer.delete(11, 16);
buffer.reverse();
System.out.println(buffer.toString()); // Outputs: avaJ ,olleH
This shows how the sequence is manipulated step-by-step using various methods.
Comparison with the Immutable String Class
Why Strings Are Immutable
Java String objects are immutable by design, meaning their value cannot be changed after creation. This immutability offers:
- Thread safety without synchronization.
- Simplified programming models.
- Security benefits by preventing data tampering.
Drawbacks of Immutability
The downside is performance overhead when performing repeated string modifications:
- Each change creates a new String object.
- Frequent concatenations result in many temporary objects.
- Increased memory usage and garbage collection pressure.
How StringBuffer and StringBuilder Improve Efficiency
By offering mutable sequences of characters, StringBuffer and StringBuilder allow modifications to occur in-place, reducing the number of temporary objects created and improving performance.
Thus, for extensive string manipulation tasks, these mutable classes are preferred over plain Strings.
Advanced Concepts: StringBuffer vs StringBuilder in Modern Java
StringBuilder was introduced in Java 5 to provide a faster alternative to StringBuffer for single-threaded scenarios.
Before this, developers either used StringBuffer (with synchronization overhead) or concatenated Strings (with performance issues).
String Concatenation and Compiler Optimization
In modern Java, the compiler often optimizes string concatenations using the StringBuilder internally.
Example:
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String result = «Hello » + «World»;
It is compiled as:
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StringBuilder sb = new StringBuilder();
sb.append(«Hello «);
sb.append(«World»);
String result = sb.toString();
This optimization makes the use of StringBuilder implicit in many cases.
When to Use Explicit StringBuilder or StringBuffer
Despite compiler optimizations, explicit use of StringBuilder or StringBuffer is beneficial when:
- Strings are constructed inside loops.
- Complex conditional concatenations occur.
- Multiple modifications to a string happen sequentially.
IndexOutOfBoundsException
Many methods like insert(), delete(), and replace() require valid index ranges. If invalid indices are provided, an IndexOutOfBoundsException will be thrown.
Example:
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StringBuilder sb = new StringBuilder(«Hello»);
sb.delete(2, 10); // Throws IndexOutOfBoundsException because end > length
Always validate indices or use try-catch blocks where necessary.
Null Pointer Exceptions
Appending or inserting a null string does not cause an exception; instead, the literal «null» string is appended.
Example:
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StringBuilder sb = new StringBuilder(«Test»);
sb.append(null);
System.out.println(sb.toString()); // Outputs: Testnull
Be cautious when appending objects that might be null.
Capacity Overflow
Although rare, extremely large strings might cause the internal character array to exceed the maximum array size, resulting in an OutOfMemoryError or other runtime errors.
Performance Comparison Between StringBuffer and StringBuilder
StringBuffer and StringBuilder are both designed for mutable string manipulation, but differ significantly in performance due to synchronization.
- StringBuffer methods are synchronized to ensure thread safety.
- StringBuilder methods are not synchronized, which makes it faster in single-threaded scenarios.
Understanding these performance differences helps developers select the right class based on the context.
Benchmarking Append Operations
The append operation is one of the most commonly used string manipulation tasks. A simple benchmark can illustrate the difference in performance.
Example Benchmark Setup
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public class PerformanceTest {
public static void main(String[] args) {
final int iterations = 100000;
long start, end;
// Test StringBuffer
StringBuffer stringBuffer = new StringBuffer();
start = System.currentTimeMillis();
for (int i = 0; i < iterations; i++) {
stringBuffer.append(«Test»);
}
end = System.currentTimeMillis();
System.out.println(«StringBuffer time: » + (end — start) + «ms»);
// Test StringBuilder
StringBuilder stringBuilder = new StringBuilder();
start = System.currentTimeMillis();
for (int i = 0; i < iterations; i++) {
stringBuilder.append(«Test»);
}
end = System.currentTimeMillis();
System.out.println(«StringBuilder time: » + (end — start) + «ms»);
}
}
Expected Results
Typically, the output shows StringBuilder completing the task in about half or less time than StringBuffer due to the lack of synchronization overhead.
Why Synchronization Impacts Performance
The synchronized keyword enforces locking, which:
- Adds overhead from acquiring and releasing locks.
- Forces threads to wait if the lock is held by another thread.
- Increases context switching and CPU resource usage.
This overhead is especially visible in tight loops or performance-critical code.
How Synchronization Works in Java
Java synchronization is built on the concept of monitors and locks. Every object in Java has an associated monitor. When a thread enters a synchronized block or method, it requests the monitor lock.
Only one thread can hold the lock at a time. Other threads are blocked until the lock is released.
StringBuffer Synchronization Model
All mutating methods in StringBuffer are synchronized, ensuring:
- Mutual exclusion on the object’s internal character array.
- Safe publication of modifications across threads.
Example synchronized method signature in StringBuffer:
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public synchronized StringBuffer append(String str) {
// method body
}
This ensures that even if multiple threads call append(), the internal state remains consistent.
Risks of Using StringBuilder in Multithreaded Environments
Because StringBuilder methods lack synchronization, concurrent access may cause:
- Data corruption.
- Inconsistent or partial writes.
- Unexpected exceptions or undefined behavior.
To safely use StringBuilder in a multithreaded context, external synchronization is necessary, for example:
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StringBuilder sb = new StringBuilder();
synchronized(sb) {
sb.append(«Safe»);
}
However, this often negates the performance benefit compared to StringBuffer.
Using StringBuilder in Shared Mutable Contexts
Mistake: Assuming StringBuilder is thread-safe by default.
Consequence: Race conditions cause unpredictable results.
Fix: Either switch to StringBuffer or apply external synchronization.
Ignoring Index Boundaries
Mistake: Using invalid indices in methods like insert(), delete(), or replace().
Consequence: IndexOutOfBoundsException crashes the program.
Fix: Validate indices carefully or use try-catch blocks.
Misunderstanding the Immutability of Strings
Mistake: Expecting a String to change when modified via methods.
Consequence: Surprising behavior because Strings are immutable.
Fix: Use StringBuilder/StringBuffer for mutable strings.
Best Practices for String Manipulation in Java
Since it is faster and uses less overhead, StringBuilder should be the default choice unless thread safety is required.
Use StringBuffer Only When Needed for Thread Safety
If your code shares mutable strings across threads and requires synchronization, use StringBuffer.
Initialize Capacity When Possible
If the approximate final size of the string is known, specify the initial capacity to reduce resizing overhead.
Example:
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StringBuilder sb = new StringBuilder(1000);
Convert to String When Done
Once string modifications are complete, convert to a String to get an immutable representation for safe sharing.
Example:
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String finalString = sb.toString();
Avoid Mixing String and StringBuilder/StringBuffer Operations Excessively
For example, avoid appending Strings frequently inside a loop to reduce the creation of temporary String objects.
Example: Building a CSV Line
Using StringBuilder to construct a comma-separated values line efficiently:
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StringBuilder csvLine = new StringBuilder();
String[] values = {«Alice», «Bob», «Charlie»};
for (int i = 0; i < values.length; i++) {
csvLine.append(values[i]);
if (i < values.length — 1) {
csvLine.append(«,»);
}
}
System.out.println(csvLine.toString()); // Outputs: Alice,Bob,Charlie
This approach is more efficient than concatenating Strings repeatedly.
Example: Logging Messages in a Multi-threaded Server
Using StringBuffer for thread-safe logging:
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public class Logger {
private StringBuffer logBuffer = new StringBuffer();
public synchronized void log(String message) {
logBuffer.append(message).append(«\n»);
}
public synchronized String getLogs() {
return logBuffer.toString();
}
}
Multiple threads can safely append logs without corrupting the buffer.
Example: Dynamic SQL Query Construction
Using StringBuilder to build SQL query strings dynamically:
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StringBuilder query = new StringBuilder(«SELECT * FROM users WHERE 1=1»);
if (filterByAge) {
query.append(» AND age > 18″);
}
if (filterByStatus) {
Query.append(» AND status = ‘ACTIVE'»);
}
String sqlQuery = query.toString();
This avoids creating multiple intermediate String objects.
Source Code Overview of StringBuilder
StringBuilder internally extends AbstractStringBuilder, which handles the character array and core operations.
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public final class StringBuilder extends AbstractStringBuilder implements java.io.Serializable, CharSequence {
public StringBuilder() {
super(16);
}
public StringBuilder(int capacity) {
super(capacity);
}
// Other methods…
}
AbstractStringBuilder Class
This class manages the character array, length, and provides synchronized or unsynchronized implementations used by subclasses.
Key fields include:
- Char [] value: The character array storing the sequence.
Intt count: Current number of characters.
StringBuffer Class
StringBuffer also extends AbstractStringBuilder but adds synchronization to each method.
Synchronization is achieved using the synchronized keyword on methods to ensure exclusive access.
From String to StringBuffer or StringBuilder
You can initialize mutable strings from an existing immutable String:
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String s = «Hello»;
StringBuffer sbuf = new StringBuffer(s);
StringBuilder sbuilder = new StringBuilder(s);
From StringBuffer or StringBuilder to String
Use the toString() method to get an immutable String copy:
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String s = sbuf.toString();
Converting Between StringBuffer and StringBuilder
Direct conversion is not possible. Use intermediate String conversion:
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StringBuffer sbuf = new StringBuffer(«Example»);
StringBuilder sbuilder = new StringBuilder(sbuf.toString());
StringJoiner
Introduced in Java 8, StringJoiner helps join strings with delimiters efficiently.
Example:
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StringJoiner joiner = new StringJoiner(«, «);
joiner.add(«Apple»).add(«Banana»).add(«Cherry»);
String result = joiner.toString(); // Outputs: Apple, Banana, Cherry
Formatter and MessageFormat
For formatted strings, these classes provide alternatives to manual concatenation with StringBuilder.
Example:
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String message = String.format(«Name: %s, Age: %d», name, age);
Using CharBuffer and Other NIO Classes
For lower-level character buffer management, Java. Nio packages provide advanced utilities, though not commonly used for typical string building.
Final Thoughts
StringBuffer and StringBuilder both serve crucial roles in Java’s string handling capabilities, balancing performance and thread safety.
Use StringBuilder when thread safety is not a concern to maximize speed and minimize overhead. Use StringBuffer only in multi-threaded contexts that require synchronized mutable strings.
Understanding the internal workings, synchronization implications, and API methods allows developers to write efficient and correct Java code involving strings.
By choosing the right class and following best practices like capacity initialization and final conversion to an immutable String, you can optimize performance and avoid common pitfalls.