StringBuilder Class in Java: Explained in Detail

Strings in Java, once declared, are immutable, and changes like appending, deleting and replacing cannot be made to the object that has been declared. StringBuilder in Java allows you to make changes to strings in real-time.   

StringBuilder class is a part of java.lang package and was introduced in Java 5 as a more efficient alternative to the older StringBuffer class. This blog will discuss StringBuilder in Java, its important Constructors and methods, and an example of its functionality. Read this blog to learn further! 

Table of Contents 

1) What is StringBuilder in Java?  

2) Important Constructors of StringBuilder in Java 

3) Important methods of StringBuilder in Java  

4) Java StringBuilder Example 

5) Conclusion 

What is StringBuilder in Java?  

StringBuilder in Java allows you to create a mutable sequence of characters. It is similar to String but allows efficient modification of its contents without creating a new object. In other words, a StringBuilder can dynamically build and modify strings as necessary.   

When a new StringBuilder object is created, it can initially hold a certain number of characters. This capacity can be increased as needed, as more characters can be added to the sequence. The size of the StringBuilder is the number of characters currently in the sequence, while the capacity is the maximum number of characters it can hold without needing to resize.   

StringBuilder can also be used with StringBuffer, a thread-safe version of StringBuilder. The main difference between the two is that StringBuilder is not thread-safe, meaning multiple threads cannot access it simultaneously. At the same time, StringBuffer can be used by multiple threads simultaneously.   

StringBuilder provides a convenient way to efficiently build and modify strings in Java, making it a useful tool for many programming tasks.
   

Important Constructors of StringBuilder in Java

The important Constructors of StringBuilder in Java are as follows: 
  

The important Constructors of StringBuilder in Java are as follows: 

1) StringBuilder(): This Constructor allows you to create an empty StringBuilder object with an initial capacity of 16 characters.  

2) StringBuilder(int capacity): This Constructor allows you to create an empty StringBuilder object with the specified initial capacity.  

3) StringBuilder(CharSequence seq): This Constructor allows you to create a StringBuilder object initialised with the contents of the specified CharSequence, such as a String or a StringBuilder.  

4) StringBuilder(String str): This Constructor allows you to create a StringBuilder object initialised with the contents of the specified string.  

All four Constructors create a StringBuilder object that can manipulate strings dynamically. Once you have a StringBuilder object, you can use various methods to manipulate its string. Unlike the immutable String class, the StringBuilder class is mutable, which means you can modify its contents without creating a new object.   

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Important methods of StringBuilder in Java 

Here are some important methods of StringBuilder in Java: 

1) append(): This method is used to append a string or character to the end of a StringBuilder object.  

2) insert(): This method is used to insert a string or character at a specified position in a StringBuilder object.  

3) delete(): This method is used to delete a string or character or a specified portion of a StringBuilder object.  

4) replace(): This method is used to replace a string or character or a specified portion of a StringBuilder object with a new string.  

5) substring(): This method is used to obtain a substring of the StringBuilder object.  

6) length(): This method is used to obtain the length of the entire StringBuilder object or a selected portion of it. 

7) capacity(): This method is used to understand the current capacity of the StringBuilder object.  

8) ensureCapacity(): This method is used to ensure that the StringBuilder object has a minimum capacity.  

9) trimToSize(): This method is used to trim the capacity of the StringBuilder object to its current length.

10) toString(): This method is used to convert the entire StringBuilder object or a portion of it to a string.

11) reverse(): This method is used to reverse the characters in the entire StringBuilder object or a selection portion of it.

12) charAt(): This method is used to get the character at a specified index in the StringBuilder object.

13) setCharAt(): This method is used to set the character at a specified index in the StringBuilder object.  

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Java StringBuilder Example 
 

import java.util.Scanner;
public class StringBuilderExample
{ 
     public static void main(String[] args) ;
{ 
    Scanner scanner = new Scanner(System.in);
    System.out.print("Enter a sentence: ");
    String sentence = scanner.nextLine();
    StringBuilder sb = new StringBuilder();
    // Loop through each character in the sentence 
    for (int i = 0; i < sentence.length(); i++)
       {
          char c = sentence.charAt(i);
          // If the character is a space, add it to the string builder if (c == ' ')
        {
           sb.append(c);
        }
         else
         {
           // Otherwise, check if the character is a letter
            if (Character.isLetter(c))
             {
                // If it's the first letter in a word, capitalize it
                if (i == 0 || sentence.charAt(i - 1) == ' ')
               {
                 sb.append(Character.toUpperCase(c));
             }
        else
        {
           // Otherwise, add it in lowercase sb.append(Character.toLowerCase(c))
        }
     }
      else
    {
        // If the character is not a letter, add it as-is sb.append(c);
       }
    }
  }
    System.out.println("Formatted sentence: " + sb.toString());
   }
}

This program formats a user-input sentence by capitalising the first letter of each word and converting all other letters to lowercase. It also preserves any punctuation and spaces.  

It accomplishes this by looping through each character in the input string, checking if it's a letter or a space, and then appending the appropriate character to the StringBuilder. The resulting string is then printed to the console. 

Conclusion 

Introduced as a replacement for the more volatile StringBuffer, StringBuilder provides a more convenient and faster way to edit string objects. StringBuilder is also non-synchronous, meaning multiple threads can access the StringBuilder object simultaneously.  

In conclusion, StringBuilder in Java is a fundamental aspect that programmers must know and understand fully.

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