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• The String class allows us to create strings which are unmodifiable i.e. immmutable strings, but by using the StringBuilder class we can create strings which are modifiable i.e. mutable strings.


• StringBuilder class is faster to execute than StringBuffer class, but its methods are not synchronized and therefore it is not a thread-safe class, whereas, StringBuffer is a thread-safe class.

When StringBuilder class is used?

• Strings created by StringBuilder class are modifiable, hence this class is used to create an application that requires creation and modification of a large volume of strings.


• StringBuilder class is fast to execute, hence it is used in the creation of applications that require a fast modification of strings of characters.

Constructors of StringBuilder class

• public StringBuilder()

  Creates a StringBuilder object with initial capacity of 16 characters.
  



• public StringBuilder(String str)

  Creates a StringBuilder object using a String str.
  



• public StringBuilder(int capacity)

  Creates a StringBuilder object with a defined capacity of characters.
  

Creating an empty StringBuilder object

• In the upcoming example, we will first will create an empty StringBuilder object by calling its constructor that takes no value.
• Next, we will modify this StringBuilder object by calling its append() method, to add String values to it.

// Java - Example of StringBuilder class

class StringBuilderEx
{
public static void main(String... ar)
{
	//Creating an empty StringBuilder object.
	StringBuilder sb= new StringBuilder(); 
	
	//Printing the empty StringBuilder object
	System.out.println("Original StringBuilder value : "+ sb);
	
	//Appending a new String, Blue, to the StringBuilder object
	sb.append("Blue");
	
	//Appending a new String, Budgie, to the StringBuilder object
	sb.append("Budgie");
	
	//Printing the modified StringBuilder object
	System.out.println("Modified StringBuilder value : "+ sb);
}
}

Output is :

Original StringBuilder value is : 
Modified StringBuilder value is : BlueBudgie

Program Analysis

• In the example, we have first created an empty StringBuilder object and have printed its empty value.
• Next, the append() method of StringBuilder class is called to append a String, Blue to the StringBuilder object.
• Again, the append() method is called to append a String, Budgie to the StringBuilder object.
• Finally, we have printed the modified value of StringBuilder object i.e. BlueBudgie.

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Creating and initializing a StringBuilder object using a String

• In the next example, we will first create a StringBuilder object by calling its constructor that takes a String.
• Next, we will modify this StringBuilder object by calling its append() method, to add new some String values to it.

// Java - Example of StringBuilder class

class StringBuilderEx
{
public static void main(String... ar)
{
	//Creating a StringBuilder object
	StringBuilder sb= new StringBuilder("Blue");

	//Printing the StringBuilder object
	System.out.println("Original StringBuilder value : "+ sb);
	
	//Appending a new String to the StringBuilder object
	sb.append("Sky");
	
	//Printing the modified value of the StringBuilder object
	System.out.println("Modified StringBuilder value : "+ sb);
}
}

Output is :

Original StringBuilder value : Blue
Modified StringBuilder value : BlueSky

Program Analysis

• In the example, we have first created a StringBuilder object which is initialized with a String value, Blue.
• Next, we have called the append() method of StringBuilder class to append a String value, Sky to the StringBuilder object.
• Finally, we have printed the modified value of our StringBuilder object i.e. BlueSky.

Reversing the string created by StringBuilder class

In the next example, we will modify the content of a string created by StringBuilder class by calling its reverse method.

// Java - Example of StringBuilder class

class A
{
public static void main(String... ar()
{
	//Creating a StringBuilder object
	StringBuilder sb= new StringBuilder("Hello"); 
	
	//Printing the StringBuilder object
	System.out.println("Original StringBuilder value : "+ sb); 
	
	//Reversing the original string within StringBuilder object
	sb.reverse();
	
	//Printing the modified StringBuilder object
	System.out.println("Modified reverse StringBuilder value : "+ sb);
}

Output is :

Original StringBuffer string value : Hello
Modified reverse StringBuilder value : olleh

For more useful method of StringBuilder class, please read our tutorial, methods of StringBuilder class.

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