StringBuffer is a class in Java that represents a mutable sequence of characters. It provides an alternative to the immutable String class, allowing you to modify the contents of a string without creating a new object every time.
Here are some important features and methods of the StringBuffer class:
- StringBuffer objects are mutable, meaning that you can change the contents of the buffer without creating a new object.
- The initial capacity of a StringBuffer can be specified when it is created, or it can be set later with the ensureCapacity() method.
- The append() method is used to add characters, strings, or other objects to the end of the buffer.
- The insert() method is used to insert characters, strings, or other objects at a specified position in the buffer.
- The delete() method is used to remove characters from the buffer.
- The reverse() method is used to reverse the order of the characters in the buffer.
Here is an example of using StringBuffer to concatenate strings:
Java
public class StringBufferExample { public static void main(String[] args) { StringBuffer sb = new StringBuffer(); sb.append("Hello"); sb.append(" "); sb.append("world"); String message = sb.toString(); System.out.println(message); }} |
Hello world
There are several advantages of using StringBuffer over regular String objects in Java:
- Mutable: StringBuffer objects are mutable, which means that you can modify the contents of the object after it has been created. In contrast, String objects are immutable, which means that you cannot change the contents of a String once it has been created.
- Efficient: Because StringBuffer objects are mutable, they are more efficient than creating new String objects each time you need to modify a string. This is especially true if you need to modify a string multiple times, as each modification to a String object creates a new object and discards the old one.
- Thread-safe: StringBuffer objects are thread-safe, which means multiple threads can access it simultaneously( they can be safely accessed and modified by multiple threads simultaneously). In contrast, String objects are not thread-safe, which means that you need to use synchronization if you want to access a String object from multiple threads.
Overall, if you need to perform multiple modifications to a string, or if you need to access a string from multiple threads, using StringBuffer can be more efficient and safer than using regular String objects.
StringBuffer is a peer class of String that provides much of the functionality of strings. The string represents fixed-length, immutable character sequences while StringBuffer represents growable and writable character sequences. StringBuffer may have characters and substrings inserted in the middle or appended to the end. It will automatically grow to make room for such additions and often has more characters preallocated than are actually needed, to allow room for growth.
StringBuffer class is used to create mutable (modifiable) strings. The StringBuffer class in Java is the same as the String class except it is mutable i.e. it can be changed.
Important Constructors of StringBuffer class
- StringBuffer(): creates an empty string buffer with an initial capacity of 16.
- StringBuffer(String str): creates a string buffer with the specified string.
- StringBuffer(int capacity): creates an empty string buffer with the specified capacity as length.
1. append() method
The append() method concatenates the given argument with this string.
Example:
Java
import java.io.*;class A { public static void main(String args[]) { StringBuffer sb = new StringBuffer("Hello "); sb.append("Java"); // now original string is changed System.out.println(sb); }} |
Hello Java
2. insert() method
The insert() method inserts the given string with this string at the given position.
Example:
Java
import java.io.*;class A { public static void main(String args[]) { StringBuffer sb = new StringBuffer("Hello "); sb.insert(1, "Java"); // Now original string is changed System.out.println(sb); }} |
HJavaello
3. replace() method
The replace() method replaces the given string from the specified beginIndex and endIndex-1.
Example:
Java
import java.io.*;class A { public static void main(String args[]) { StringBuffer sb = new StringBuffer("Hello"); sb.replace(1, 3, "Java"); System.out.println(sb); }} |
HJavalo
4. delete() method
The delete() method of the StringBuffer class deletes the string from the specified beginIndex to endIndex-1.
Example:
Java
import java.io.*;class A { public static void main(String args[]) { StringBuffer sb = new StringBuffer("Hello"); sb.delete(1, 3); System.out.println(sb); }} |
Hlo
5. reverse() method
The reverse() method of the StringBuilder class reverses the current string.
Example:
Java
import java.io.* ;class A { public static void main(String args[]) { StringBuffer sb = new StringBuffer("Hello"); sb.reverse(); System.out.println(sb); }} |
olleH
6. capacity() method
- The capacity() method of the StringBuffer class returns the current capacity of the buffer. The default capacity of the buffer is 16. If the number of characters increases from its current capacity, it increases the capacity by (oldcapacity*2)+2.
- For instance, if your current capacity is 16, it will be (16*2)+2=34.
Example:
Java
import java.io.*;class A { public static void main(String args[]) { StringBuffer sb = new StringBuffer(); System.out.println(sb.capacity()); // default 16 sb.append("Hello"); System.out.println(sb.capacity()); // now 16 sb.append("java is my favourite language"); System.out.println(sb.capacity()); // Now (16*2)+2=34 i.e (oldcapacity*2)+2 }} |
16 16 34
Some Interesting Facts about the StringBuffer class
Do keep the following points in the back of your mind:
- java.lang.StringBuffer extends (or inherits from) Object class.
- All Implemented Interfaces of StringBuffer class: Serializable, Appendable, CharSequence.
- public final class StringBuffer extends Object implements Serializable, CharSequence, Appendable.
- String buffers are safe for use by multiple threads. The methods can be synchronized wherever necessary so that all the operations on any particular instance behave as if they occur in some serial order.
- Whenever an operation occurs involving a source sequence (such as appending or inserting from a source sequence) this class synchronizes only on the string buffer performing the operation, not on the source.
- It inherits some of the methods from the Object class which such as clone(), equals(), finalize(), getClass(), hashCode(), notifies(), notifyAll().
Remember: StringBuilder, J2SE 5 adds a new string class to Java’s already powerful string handling capabilities. This new class is called StringBuilder. It is identical to StringBuffer except for one important difference: it is not synchronized, which means that it is not thread-safe. The advantage of StringBuilder is faster performance. However, in cases in which you are using multithreading, you must use StringBuffer rather than StringBuilder.
Constructors of StringBuffer class
1. StringBuffer(): It reserves room for 16 characters without reallocation
StringBuffer s = new StringBuffer();
2. StringBuffer( int size): It accepts an integer argument that explicitly sets the size of the buffer.
StringBuffer s = new StringBuffer(20);
3. StringBuffer(String str): It accepts a string argument that sets the initial contents of the StringBuffer object and reserves room for 16 more characters without reallocation.
StringBuffer s = new StringBuffer("Lazyroar");
Methods of Java StringBuffer class
| Methods | Action Performed |
|---|---|
| append() | Used to add text at the end of the existing text. |
| length() | The length of a StringBuffer can be found by the length( ) method |
| capacity() | the total allocated capacity can be found by the capacity( ) method |
| charAt() | This method returns the char value in this sequence at the specified index. |
| delete() | Deletes a sequence of characters from the invoking object |
| deleteCharAt() | Deletes the character at the index specified by the loc |
| ensureCapacity() | Ensures capacity is at least equal to the given minimum. |
| insert() | Inserts text at the specified index position |
| length() | Returns the length of the string |
| reverse() | Reverse the characters within a StringBuffer object |
| replace() | Replace one set of characters with another set inside a StringBuffer object |
Note: Besides that, all the methods that are used in the String class can also be used. These auxiliary methods are as follows:
|
Methods |
Description |
Syntax |
|---|---|---|
|
It is used to increase the capacity of a StringBuffer object. The new capacity will be set to either the value we specify or twice the current capacity plus two (i.e. capacity+2), whichever is larger. Here, capacity specifies the size of the buffer. |
void ensureCapacity(int capacity) |
|
|
This method appends the string representation of the codePoint argument to this sequence. |
public StringBuffer appendCodePoint(int codePoint) |
|
|
charAt(int index) |
This method returns the char value in this sequence at the specified index. |
public char charAt(int index) |
|
IntStream chars() |
This method returns a stream of int zero-extending the char values from this sequence. |
public IntStream chars() |
|
This method returns the character (Unicode code point) at the specified index. |
public int codePointAt(int index) |
|
|
This method returns the character (Unicode code point) before the specified index. |
public int codePointBefore(int index) |
|
|
This method returns the number of Unicode code points in the specified text range of this sequence. |
public int codePointCount(int beginIndex, int endIndex) |
|
|
IntStream codePoints() |
This method returns a stream of code point values from this sequence. |
public IntStream codePoints() |
|
void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) |
In this method, the characters are copied from this sequence into the destination character array dst. |
public void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) |
|
This method returns the index within this string of the first occurrence of the specified substring. |
public int indexOf(String str) |
|
|
This method returns the index within this string of the last occurrence of the specified substring. |
public int lastIndexOf(String str) |
|
|
This method returns the index within this sequence that is offset from the given index by codePointOffset code points. |
public int offsetByCodePoints(int index, int codePointOffset) |
|
|
In this method, the character at the specified index is set to ch. |
public void setCharAt(int index, char ch) |
|
|
This method sets the length of the character sequence. |
public void setLength(int newLength) |
|
|
This method returns a new character sequence that is a subsequence of this sequence. |
public CharSequence subSequence(int start, int end) |
|
|
This method returns a new String that contains a subsequence of characters currently contained in this character sequence. |
public String substring(int start) |
|
|
This method returns a string representing the data in this sequence. |
public String toString() |
|
|
This method attempts to reduce storage used for the character sequence. |
public void trimToSize() |
Above we only have discussed the most widely used methods and do keep a tight bound around them as they are widely used in programming geeks.
Examples of the above methods
Example 1: length() and capacity() Methods
Java
// Java Program to Illustrate StringBuffer class// via length() and capacity() methods// Importing I/O classesimport java.io.*;// Main classclass GFG { // main driver method public static void main(String[] args) { // Creating and storing string by creating object of // StringBuffer StringBuffer s = new StringBuffer("Lazyroar"); // Getting the length of the string int p = s.length(); // Getting the capacity of the string int q = s.capacity(); // Printing the length and capacity of // above generated input string on console System.out.println("Length of string Lazyroar=" + p); System.out.println( "Capacity of string Lazyroar=" + q); }} |
Length of string Lazyroar=13 Capacity of string Lazyroar=29
Example 2: append()
It is used to add text at the end of the existing text.
Here are a few of its forms:
StringBuffer append(String str)
StringBuffer append(int num)
Java
// Java Program to Illustrate StringBuffer class// via append() method// Importing required classesimport java.io.*;// Main classclass GFG { // Main driver method public static void main(String[] args) { // Creating an object of StringBuffer class and // passing random string StringBuffer s = new StringBuffer("Geeksfor"); // Usage of append() method s.append("Geeks"); // Returns Lazyroar System.out.println(s); s.append(1); // Returns Lazyroar1 System.out.println(s); }} |
Lazyroar Lazyroar1
Example 3: insert()
It is used to insert text at the specified index position.
Syntax: These are a few of its as follows:
StringBuffer insert(int index, String str)
StringBuffer insert(int index, char ch)
Here, the index specifies the index at which point the string will be inserted into the invoking StringBuffer object.
Java
// Java Program to Illustrate StringBuffer class// via insert() method// Importing required I/O classesimport java.io.*;// Main classclass GFG { // Main driver method public static void main(String[] args) { // Creating an object of StringBuffer class StringBuffer s = new StringBuffer("GeeksGeeks"); // Inserting element and position as an arguments s.insert(5, "for"); // Returns Lazyroar System.out.println(s); s.insert(0, 5); // Returns 5Lazyroar System.out.println(s); s.insert(3, true); // Returns 5GetrueeksforGeeks System.out.println(s); s.insert(5, 41.35d); // Returns 5Getr41.35ueeksforGeeks System.out.println(s); s.insert(8, 41.35f); // Returns 5Getr41.41.3535ueeksforGeeks System.out.println(s); // Declaring and initializing character array char geeks_arr[] = { 'p', 'a', 'w', 'a', 'n' }; // Inserting character array at offset 9 s.insert(2, geeks_arr); // Returns 5Gpawanetr41.41.3535ueeksforGeeks System.out.println(s); }} |
Lazyroar 5Lazyroar 5GetrueeksforGeeks 5Getr41.35ueeksforGeeks 5Getr41.41.3535ueeksforGeeks 5Gpawanetr41.41.3535ueeksforGeeks
Example 4: reverse( )
It can reverse the characters within a StringBuffer object using reverse( ). This method returns the reversed object on which it was called.
Java
// Java Program to Illustrate StringBuffer class// via reverse() method// Importing I/O classesimport java.io.*;// Main classclass GFG { // Main driver method public static void main(String[] args) { // Creating a string via creating // object of StringBuffer class StringBuffer s = new StringBuffer("GeeksGeeks"); // Invoking reverse() method s.reverse(); // Returns "skeeGrofskeeG" System.out.println(s); }} |
skeeGskeeG
Example 5: delete( ) and deleteCharAt()
It can delete characters within a StringBuffer by using the methods delete( ) and deleteCharAt( ).The delete( ) method deletes a sequence of characters from the invoking object. Here, the start Index specifies the index of the first character to remove, and the end Index specifies an index one past the last character to remove. Thus, the substring deleted runs from start Index to endIndex–1. The resulting StringBuffer object is returned. The deleteCharAt( ) method deletes the character at the index specified by loc. It returns the resulting StringBuffer object.
Syntax:
StringBuffer delete(int startIndex, int endIndex)
StringBuffer deleteCharAt(int loc)
Java
// Java Program to Illustrate StringBuffer class// via delete() and deleteCharAt() Methods// Importing I/O classesimport java.io.*;// Main classclass GFG { // Main driver method public static void main(String[] args) { StringBuffer s = new StringBuffer("Lazyroar"); s.delete(0, 5); // Returns forGeeks System.out.println(s); s.deleteCharAt(7); // Returns forGeek System.out.println(s); }} |
forGeeks forGeek
Example 6: replace()
It can replace one set of characters with another set inside a StringBuffer object by calling replace( ). The substring being replaced is specified by the indexes start Index and endIndex. Thus, the substring at start Index through endIndex–1 is replaced. The replacement string is passed in str. The resulting StringBuffer object is returned.
Syntax:
StringBuffer replace(int startIndex, int endIndex, String str)
Example
Java
// Java Program to Illustrate StringBuffer class// via replace() method// Importing I/O classesimport java.io.*;// Main classclass GFG { // Main driver method public static void main(String[] args) { StringBuffer s = new StringBuffer("Lazyroar"); s.replace(5, 8, "are"); // Returns GeeksareGeeks System.out.println(s); }} |
GeeksareGeeks
This article is contributed by Lokesh Todwal. Please write comments if you find anything incorrect, or if you want to share more information about the topic discussed above.
