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Although both StringBuilder class and StringBuffer class are used to create a string of characters which are modifiable, there are a few differences between them. Let's discuss those.

Differences between StringBuffer class and StringBuilder class.

Creating and initializing a StringBuffer object using a String

• We will create a StringBuffer class object by calling its constructor that a String.
• We will modify this StringBuffer object by calling its append() method, to add new String values to it.

// Java - Example of StringBuffer class

class StringBufferEx
{
public static void main(String... ar)
{
	//Creating and initializing a StringBuffer object using a String value
	StringBuffer sb= new StringBuffer("Keep");

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

Output is :

Original StringBuffer value : Keep
Modified StringBuffer value : KeepSmiling

Program Analysis

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

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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("Happy");

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

Output is :

Original StringBuilder value : Happy
Modified StringBuilder value : HappyFaces

Program Analysis

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

Execution speed of StringBuffer & StringBuilder

In the next example, we are going to prove that the execution speed of StringBuffer class is slower than StringBuilder. For this, we will perform the append operation by calling the append() method of each class, 50000 times.

// Java - Difference between the execution speed of StringBuffer & StringBuilder class


class BuffBuild 
{
public static void main(String[] args) 
{
	int counter = 50000;

	//Creating an empty StringBuffer object
	StringBuffer sb1 = new StringBuffer();
	
	//Getting the current starting time 
	long startTime = System.currentTimeMillis();    	


	//Using for loop to call the append() method of StringBuffer, 5000 times
	for (int i = 0; i<counter; i++) 
	{
		sb1.append("StringBuffer");
	}
	
	//Getting the time taken by StringBuffer
	long timeTaken = System.currentTimeMillis()-startTime();
	
	//Printing the time taken by StringBuffer to call the append() method, 5000 times
	System.out.println("Milliseconds taken by StringBuffer  to append() 50000 times : " + timeTaken);
        
		
	//Creating an empty StringBuffer object  
	StringBuilder sb2 = new StringBuilder();
	
	//Getting the current starting time
	startTime = System.currentTimeMillis(); 		

	//Using for loop to call the append() method of StringBuffer, 5000 times
	for (int i = 0; i<counter; i++)
	{
		sb2.append("StringBuilder");
	}
	
	//Calculating the time taken by StringBuilder
	timeTaken = System.currentTimeMillis()-startTime();
    
	//Printing the time taken by StringBuilder to call the append() method, 5000 times
	System.out.println("Milliseconds taken by StringBuilder to append() 50000 times : " + timeTaken);
        
}
}

Output is :

Milliseconds taken by StringBuffer  class to append() 50000 times : 21
Milliseconds taken by StringBuilder class to append() 50000 times : 15

Program Analysis

• A static method currentTimeMillis() of System class is used to get the current time in milliseconds.
• Time taken to perform append() method of StringBuffer class, 50000 times is 21 ms.
• Time taken to perform append() method of StringBuilder class 50000 times is even faster, 15 ms.

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