StringBuffer class in Java

22 Apr, 2022
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.
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("GeeksforGeeks");
Methods of StringBuffer class 
Note: Besides that, all the methods that are used in the String class can also be used. These auxiliary methods are as follows:
ensureCapacity()
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.
Syntax:
void ensureCapacity(int capacity)
appendCodePoint(int codePoint): This method appends the string representation of the codePoint argument to this sequence.
Syntax: 
public StringBuffer appendCodePoint(int codePoint)
charAt(int index)
This method returns the char value in this sequence at the specified index.
Syntax: 
public char charAt(int index)
IntStream chars(): This method returns a stream of int zero-extending the char values from this sequence.
Syntax: 
public IntStream chars()
int codePointAt(int index): This method returns the character (Unicode code point) at the specified index.
Syntax: 
public int codePointAt(int index)
int codePointBefore(int index): This method returns the character (Unicode code point) before the specified index.
Syntax: 
public int codePointBefore(int index)
int codePointCount(int beginIndex, int endIndex): This method returns the number of Unicode code points in the specified text range of this sequence.
Syntax: 
public int codePointCount(int beginIndex, int endIndex)
IntStream codePoints(): This method returns a stream of code point values from this sequence.
Syntax: 
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.
Syntax: 
public void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
int indexOf(String str): This method returns the index within this string of the first occurrence of the specified substring.
Syntax: 
public int indexOf(String str)
public int indexOf(String str, int fromIndex)
int lastIndexOf(String str): This method returns the index within this string of the last occurrence of the specified substring.
Syntax: 
public int lastIndexOf(String str)
public int lastIndexOf(String str, int fromIndex)
int offsetByCodePoints(int index, int codePointOffset): This method returns the index within this sequence that is offset from the given index by codePointOffset code points.
Syntax: 
public int offsetByCodePoints(int index, int codePointOffset) 
void setCharAt(int index, char ch): In this method, the character at the specified index is set to ch.
Syntax: 
public void setCharAt(int index, char ch)
void setLength(int newLength): This method sets the length of the character sequence.
Syntax: 
public void setLength(int newLength)
CharSequence subSequence(int start, int end): This method returns a new character sequence that is a subsequence of this sequence.
Syntax: 
public CharSequence subSequence(int start, int end)
String substring(int start): This method returns a new String that contains a subsequence of characters currently contained in this character sequence.
Syntax: 
public String substring(int start)
public String substring(int start,int end)
String toString(): This method returns a string representing the data in this sequence.
Syntax: 
public String toString()
void trimToSize(): This method attempts to reduce storage used for the character sequence.
Syntax: 
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.
Implementation: 
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 adn storing string by creating object of        // StringBuffer        StringBuffer s = new StringBuffer("GeeksforGeeks");         // 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 GeeksforGeeks="                           + p);        System.out.println(            "Capacity of string GeeksforGeeks=" + q);    }}
Length of string GeeksforGeeks=13
Capacity of string GeeksforGeeks=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 GeeksforGeeks        System.out.println(s);         s.append(1);        // Returns GeeksforGeeks1        System.out.println(s);    }}
GeeksforGeeks
GeeksforGeeks1
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 GeeksforGeeks        System.out.println(s);         s.insert(0, 5);        // Returns 5GeeksforGeeks        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);    }}
GeeksforGeeks
5GeeksforGeeks
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("GeeksforGeeks");         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("GeeksforGeeks");        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 you want to share more information about the topic discussed above. 
ShreyasWaghmare
pujasingg43
anikakapoor
surinderdawra388
kapoorsagar226
surindertarika1234
simmytarika5
varshagumber28
paridhibhagwat2002
Java-lang package
java-StringBuffer
Java-Strings
Java
Java-Strings
Java
Writing code in comment?
Please use ide.geeksforgeeks.org,
generate link and share the link here.
Split() String method in Java with examples
Arrays.sort() in Java with examples
Reverse a string in Java
How to iterate any Map in Java
Stream In Java
Initializing a List in Java
Singleton Class in Java
Initialize an ArrayList in Java
Generics in Java
Java Programming Examples