Java - String Buffer & String Builder Classes

The StringBuffer and StringBuilder classes are used when there is a necessity to make alot of modifications to Strings of characters.

Unlike Strings objects of type StringBuffer and Stringbuilder can be modified over and over again with out leaving behind alot of new unused objects.

The StringBuilder class was introduced as of Java 5 and the main difference between the StringBuffer and StringBuilder is that StringBuilders methods are not thread safe(not Synchronised).

It is recommended to use StringBuilder whenever possible because it is faster than StringBuffer. However if thread safety is necessary the best option is StringBuffer objects.

Example:

public class Test{

    public static void main(String args[]){
       StringBuffer sBuffer = new StringBuffer(" test");
       sBuffer.append(" String Buffer");
       System.ou.println(sBuffer);  
   }
}

This would produce following result:

test String Buffer

StringBuffer Methods:

Here is the list of important methods supported by StringBuffer class:

SN	Methods with Description
1	public StringBuffer append(String s) Updates the value of the object that invoked the method. The method takes boolean, char, int, long, Strings etc.
2	public StringBuffer reverse() The method reverses the value of the StringBuffer object that invoked the method.
3	public delete(int start, int end) Deletes the string starting from start index until end index.
4	public insert(int offset, int i) This method inserts an string s at the position mentioned by offset.
5	replace(int start, int end, String str) This method replaces the characters in a substring of this StringBuffer with characters in the specified String.

Here is the list of other methods (Except set methods ) which are very similar to String class:

SN	Methods with Description
1	int capacity() Returns the current capacity of the String buffer.
2	char charAt(int index) The specified character of the sequence currently represented by the string buffer, as indicated by the index argument, is returned.
3	void ensureCapacity(int minimumCapacity) Ensures that the capacity of the buffer is at least equal to the specified minimum.
4	void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) Characters are copied from this string buffer into the destination character array dst.
5	int indexOf(String str) Returns the index within this string of the first occurrence of the specified substring.
6	int indexOf(String str, int fromIndex)  Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
7	int lastIndexOf(String str) Returns the index within this string of the rightmost occurrence of the specified substring.
8	int lastIndexOf(String str, int fromIndex) Returns the index within this string of the last occurrence of the specified substring.
9	int length() Returns the length (character count) of this string buffer.
10	void setCharAt(int index, char ch) The character at the specified index of this string buffer is set to ch.
11	void setLength(int newLength) Sets the length of this String buffer.
12	CharSequence subSequence(int start, int end)  Returns a new character sequence that is a subsequence of this sequence.
13	String substring(int start) Returns a new String that contains a subsequence of characters currently contained in this StringBuffer.The substring begins at the specified index and extends to the end of the StringBuffer.
14	String substring(int start, int end) Returns a new String that contains a subsequence of characters currently contained in this StringBuffer.
15	String toString() Converts to a string representing the data in this string buffer.

Java - String Buffer reverse() Method

Description:

This method reverses the value of the StringBuffer object that invoked the method.

Let n be the length of the old character sequence, the one contained in the string buffer just prior to execution of the reverse method. Then the character at index k in the new character sequence is equal to the character at index n-k-1 in the old character sequence.

Syntax:

Here is the syntax for this method:

public StringBuffer reverse()

Parameters:

Here is the detail of parameters:

• NA

Return Value:

• This method returns StringBuffer object with the reversed sequence.

Example:

public class Test {

    public static void main(String args[]) {
       StringBuffer buffer = new StringBuffer("Game Plan");
       buffer.reverse();
       System.out.println(buffer);
   }  
}

This produces following result:

nalP emaG

Java - String Buffer replace() Method

Description:

This method replaces the characters in a substring of this StringBuffer with characters in the specified String.

The substring begins at the specified start and extends to the character at index end - 1 or to the end of the StringBuffer if no such character exists. First the characters in the substring are removed and then the specified String is inserted at start.

Syntax:

Here is the syntax of this method:

public StringBuffer replace(int start, int end, String str)

Parameters:

Here is the detail of parameters:

• start -- The beginning index, inclusive.
• end -- The ending index, exclusive.
• str -- String that will replace previous contents.

Return Value:

• This method Returns the modified SringBuffer object.

Java - String Buffer insert() Method

Description:

This method removes the characters in a substring of this StringBuffer. The substring begins at the specified start and extends to the character at index end - 1 or to the end of the StringBuffer if no such character exists.

If start is equal to end, no changes are made.

Syntax:

Here is a separate method for each primitive data type:

public StringBuffer insert(int offset, boolean b)
public StringBuffer insert(int offset, char c)
public insert(int offset, char[] str)
public StringBuffer insert(int index, char[] str, 
                           int offset, int len)
public StringBuffer insert(int offset, float f)  
public StringBuffer insert(int offset, int i)
public StringBuffer insert(int offset, long l) 
public StringBuffer insert(int offset, Object obj) 
public StringBuffer insert(int offset, String str)

Parameters:

Here is the detail of parameters:

• Parameter depends on what you are trying to insert.

Return Value:

• This method Returns the modified SringBuffer object.
  
  

Java - String Buffer delete() Method

Description:

This method removes the characters in a substring of this StringBuffer. The substring begins at the specified start and extends to the character at index end - 1 or to the end of the StringBuffer if no such character exists.

If start is equal to end, no changes are made.

Syntax:

Here is the syntax of this method :

public StringBuffer delete(int start, int end)

Parameters:

Here is the detail of parameters:

• start -- The beginning index, inclusive.
• end -- The ending index, exclusive.

Return Value:

• This method returns the StringBuffer object.

Example:

public class Test {

   public static void main(String args[]) {
      StringBuffer sb = new StringBuffer("abcdefghijk");
      sb.delete(3,7); 
      System.out.println(sb); 
   }  
}

This produces following result:

abchijk

Java - String Buffer append() Method

Description:

This method updates the value of the object that invoked the method. The method takes boolean, char, int, long, Strings etc.

Syntax:

Here is a separate method for each primitive data type:

public StringBuffer append(boolean b)
public StringBuffer append(char c) 
public StringBuffer append(char[] str) 
public StringBuffer append(char[] str, int offset, int len) 
public StringBuffer append(double d) 
public StringBuffer append(float f)
public StringBuffer append(int i) 
public StringBuffer append(long l) 
public StringBuffer append(Object obj) 
public StringBuffer append(StringBuffer sb) 
public StringBuffer append(String str) 

Parameters:

Here is the detail of parameters:

• Here parameter depends on what you are trying to append in the String Buffer.

Return Value:

• These methods return the updated StringBuffer objects

Example:

public class Test {

   public static void main(String args[]) {
      StringBuffer sb = new StringBuffer("Test");
      sb.append(" String Buffer");
      System.out.println(sb); 
   }  
}

This produces following result:

Test String Buffer