Introduction Java StringBuilder class

The java.lang.StringBuilder class is mutable sequence of characters .StringBuilder class is used to create mutable (modifiable) string. The StringBuilder class is same as StringBuffer class except that it is non-synchronized.

Class declaration

Following is the declaration for java.lang.StringBuilder class:

public final class StringBuilder
  extends Object
   implements Serializable, CharSequence
						

Constructors of StringBuilder class:

  1. StringBuilder(): creates an empty string Builder with the initial capacity of 16.
  2. StringBuilder(String str): creates a string Builder with the specified string.
  3. StringBuilder(int length): creates an empty string Builder with the specified capacity as length.
  4. StringBuilder(CharSequence seq)This constructs a string builder that contains the same characters as the specified CharSequence.

Commonly used methods of StringBuilder class:

  1. public StringBuilder append(String s): is used to append the specified string with this string. The append() method is overloaded like append(char), append(boolean), append(int), append(float), append(double) etc.
  2. public StringBuilder insert(int offset, String s): is used to insert the specified string with this string at the specified position. The insert() method is overloaded like insert(int, char), insert(int, boolean), insert(int, int), insert(int, float), insert(int, double) etc.
  3. public StringBuilder replace(int startIndex, int endIndex, String str): is used to replace the string from specified startIndex and endIndex.
  4. public StringBuilder delete(int startIndex, int endIndex): is used to delete the string from specified startIndex and endIndex.
  5. public StringBuilder reverse(): is used to reverse the string.
  6. public int capacity(): is used to return the current capacity.
  7. public void ensureCapacity(int minimumCapacity): is used to ensure the capacity at least equal to the given minimum.
  8. public char charAt(int index): is used to return the character at the specified position.
  9. public int length(): is used to return the length of the string i.e. total number of characters.
  10. public String substring(int beginIndex): is used to return the substring from the specified beginIndex.
  11. public String substring(int beginIndex, int endIndex): is used to return the substring from the specified beginIndex and endIndex.

Java StringBuilder Examples

Let's see the examples of different methods of StringBuilder class.

1 StringBuilder append() method

The StringBuilder append() method concatenates the given argument with this string.

class A{
public static void main(String args[]){
StringBuilder sb=new StringBuilder("Hello ");
sb.append("Java");//now original string is changed
System.out.println(sb);//prints Hello Java
}
}

2 StringBuilder insert() method

The StringBuilder insert() method inserts the given string with this string at the given position.

class A{
public static void main(String args[]){
StringBuilder sb=new StringBuilder("Hello ");
sb.insert(1,"Java");//now original string is changed
System.out.println(sb);//prints HJavaello
}
}

3 StringBuilder replace() method

The StringBuilder replace() method replaces the given string from the specified beginIndex and endIndex.

class A{
public static void main(String args[]){
StringBuilder sb=new StringBuilder("Hello");
sb.replace(1,3,"Java");
System.out.println(sb);//prints HJavalo
}
}

4 StringBuilder delete() method

The delete() method of StringBuilder class deletes the string from the specified beginIndex to endIndex.

class A{
public static void main(String args[]){
StringBuilder sb=new StringBuilder("Hello");
sb.delete(1,3);
System.out.println(sb);//prints Hlo
}
}

5 StringBuilder reverse() method

The reverse() method of StringBuilder class reverses the current string.

class A{
public static void main(String args[]){
StringBuilder sb=new StringBuilder("Hello");
sb.reverse();
System.out.println(sb);//prints olleH
}
}