String Buffer and String Builder Classes


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

Unlike Strings, objects of type StringBuffer and String builder can be modified over and over again without leaving behind a lot 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 the 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.out.println(sBuffer);  
   }
}

This will produce the following result −

Output

test String Buffer

StringBuffer Methods

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

Sr.No. Methods & 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 the start index until the end index.

4 public insert(int offset, int i)

This method inserts a string s at the position mentioned by the 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 −

Sr.No. Method & 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_strings.htm

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