Explain all String Buffer methods with examples.

6.B] Explain all String Buffer methods with examples.

Answer:

The StringBuffer class in Java is used to create mutable (modifiable) strings.

Unlike String, which is immutable, StringBuffer allows strings to be changed without creating new objects. Below are some of the commonly used StringBuffer methods along with examples.

1. append(String str)

• Purpose: Adds the specified string to the end of the current StringBuffer.
• Syntax: sb.append(str);
• Example:

  StringBuffer sb = new StringBuffer("Hello");
  sb.append(" World");
  System.out.println(sb); // Output: Hello World

2. insert(int offset, String str)

• Purpose: Inserts the specified string at the given offset (position) in the StringBuffer.
• Syntax: sb.insert(offset, str);
• Example:

  StringBuffer sb = new StringBuffer("Hello World");
  sb.insert(6, "Beautiful ");
  System.out.println(sb); // Output: Hello Beautiful World

3. replace(int start, int end, String str)

• Purpose: Replaces the characters in the substring of this StringBuffer starting at the specified start index and ending at the end index with the specified string.
• Syntax: sb.replace(start, end, str);
• Example:

  StringBuffer sb = new StringBuffer("Hello World");
  sb.replace(6, 11, "Java");
  System.out.println(sb); // Output: Hello Java

4. delete(int start, int end)

• Purpose: Removes the characters in the substring from the start index to the end index.
• Syntax: sb.delete(start, end);
• Example:

  StringBuffer sb = new StringBuffer("Hello World");
  sb.delete(5, 11);
  System.out.println(sb); // Output: Hello

5. deleteCharAt(int index)

• Purpose: Removes the character at the specified position in the StringBuffer.
• Syntax: sb.deleteCharAt(index);
• Example:

  StringBuffer sb = new StringBuffer("Hello");
  sb.deleteCharAt(4);
  System.out.println(sb); // Output: Hell

6. reverse()

• Purpose: Reverses the sequence of characters in the StringBuffer.
• Syntax: sb.reverse();
• Example:

  StringBuffer sb = new StringBuffer("Hello");
  sb.reverse();
  System.out.println(sb); // Output: olleH

7. setCharAt(int index, char ch)

• Purpose: Sets the character at the specified index to the given character.
• Syntax: sb.setCharAt(index, ch);
• Example:

  StringBuffer sb = new StringBuffer("Hello");
  sb.setCharAt(1, 'a');
  System.out.println(sb); // Output: Hallo

8. setLength(int newLength)

• Purpose: Sets the length of the StringBuffer. If the new length is greater than the current length, null characters (\u0000) are added. If it’s less, the string is truncated.
• Syntax: sb.setLength(newLength);
• Example:

  StringBuffer sb = new StringBuffer("Hello");
  sb.setLength(2);
  System.out.println(sb); // Output: He

9. capacity()

• Purpose: Returns the current capacity of the StringBuffer (the amount of storage available for new characters without resizing).
• Syntax: int capacity = sb.capacity();
• Example:

  StringBuffer sb = new StringBuffer();
  System.out.println(sb.capacity()); // Output: 16 (default capacity)

10. ensureCapacity(int minimumCapacity)

• Purpose: Ensures that the StringBuffer has at least the specified capacity.
• Syntax: sb.ensureCapacity(minimumCapacity);
• Example:

  StringBuffer sb = new StringBuffer();
  sb.ensureCapacity(30);
  System.out.println(sb.capacity()); // Output: 30

11. length()

• Purpose: Returns the number of characters stored in the StringBuffer.
• Syntax: int len = sb.length();
• Example:

  StringBuffer sb = new StringBuffer("Hello");
  System.out.println(sb.length()); // Output: 5

12. substring(int start) and substring(int start, int end)

• Purpose: Returns a new string that contains a subsequence of characters currently contained in the StringBuffer. The substring begins at the specified index and extends to the end or specified end index.
• Syntax:
• String subStr = sb.substring(start);
• String subStr = sb.substring(start, end);
• Example:

  StringBuffer sb = new StringBuffer("Hello World");
  String subStr = sb.substring(6);
  System.out.println(subStr); // Output: World

Summary:

• append(): Adds text at the end.
• insert(): Inserts text at a specific position.
• replace(): Replaces a portion of the string.
• delete() and deleteCharAt(): Removes text or a specific character.
• reverse(): Reverses the string.
• setCharAt(): Changes a specific character.
• setLength(): Adjusts the length of the string.
• capacity() and ensureCapacity(): Deals with the buffer’s capacity.
• length(): Returns the current length.
• substring(): Extracts part of the string.