StringBuilder Java

StringBuilder in Java

StringBuilder class in Java is used to manipulate strings so that we can modify the value. In other, StringBuilder class is mutable. It is similar to StringBuffer and String class except that this is mutable whereas StringBuffer is immutable. The performance of StringBuilder is faster than StringBuffer and does not support multiple threads and hence is non-synchronized. In this tutorial, we will learn about the StringBuilder class and methods like append, reverse, delete,toString etc using StringBuilder Java with examples.

Constructors of Java StringBuilder

Below are the constructors of the StringBuilder class:

Methods of StringBuilder class in Java

Below are the StringBuilder methods:

Java StringBuilder Examples

In this section, we will see about the StringBuilder Java class and methods using StringBuilder Java with examples.

Example: insert() method

We can insert a specified string at the required position using the StringBuilder Java method which is insert(). The below example inserts the new string at index 2.

public class StringBuilderDemo {

  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Java");
    sb.insert(2, "Hello");
    
    System.out.println(sb);

  }

}

JaHellova

Example: append() method

The StringBuilder append method in Java appends the new string to the existing string at the end. In this example, we add a new string “language” to the existing string “Java”. Hence the output is “Java language”

public class StringBuilderDemo {

  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Java");
    sb.append(" language");
    
    System.out.println(sb);

  }

}

Java language

Example: reverse() method

The below example shows how to use the StringBuilder reverse method. This method returns a reversed string.

public class StringBuilderDemo {

  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Java");
    
    sb.reverse();
    System.out.println(sb);

  }

}

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Example: replace() method

The replace method replaces the characters with the new string starting from the specified index. In this example, it replaces the characters from index 2 to 4 with the new string.

public class StringBuilderDemo {

  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Welcome to Java tutorial");
    
    sb.replace(2, 4, "Hello");
    System.out.println(sb);

    
  }

}

WeHelloome to Java tutorial

Example: delete() method

The StringBuilder delete method deletes the characters from the specified start index until the end index. We can also delete a single character at the specified index using the deleteCharAt() method. The below example illustrates both the delete methods.

public class StringBuilderDemo {

  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Welcome to Java tutorial");

    sb.delete(2, 8);
    System.out.println("String after delete operation: " + sb);
    sb.deleteCharAt(15);
    System.out.println("String after deleteCharAt operation: " + sb);
    
  }

}

String after delete operation: Weto Java tutorial
String after deleteCharAt operation: Weto Java tutoral

Example: subString() method

The Java subString() method returns the portion of the string based on the specified index. In the below example, the first output returns the substring from index 5 and the second output returns the substring ranging between index 5 and 10.

public class StringBuilderDemo {

  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Welcome to Java tutorial");
    
    System.out.println("Substring from index 5: " + sb.substring(5));
    System.out.println("Substring ranging between index 5 and 10: " + sb.substring(5, 10));
    
  }

}

Substring from index 5: me to Java tutorial
Substring ranging between index 5 and 10: me to

Example: toString() method

The Java StringBuilder toString method returns the String representation of the specified object.

public class StringBuilderDemo {

  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Welcome to Java tutorial");
    
    String s = sb.toString();
    System.out.println("String representation: " + s);
    
  }

}

String representation: Welcome to Java tutorial

Example: length() method

We can use the length() method to calculate the StringBuilder size of the string. We can also set the new size of the StringBuilder object using the setLength() method.

public class StringBuilderDemo {

  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Welcome to Java tutorial");
    
    System.out.println("Size of string: " + sb.length());
    sb.setLength(50);
    System.out.println("New size of the string: " + sb.length());
    
  }

}

Size of string: 24
New size of the string: 50

Example: Other methods

Below is an example of other methods of the StringBuilder class. The charAt() method returns the character at the specified index. The indexOf() method returns the index of the first occurrence of the specified string. The lastIndexOf() method returns the index of the last occurrence of the specified string.

public class StringBuilderDemo {

  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Welcome to Java tutorial");
  
    System.out.println("Original string: " + sb);
    System.out.println("Char at index 3: " + sb.charAt(3));
    System.out.println("Index of string 'to' : " + sb.indexOf("to"));
    System.out.println("Last index of string 'to' : " + sb.lastIndexOf("to"));

    
  }

}

Original string: Welcome to Java tutorial
Char at index 3: c
Index of string 'to' : 8
Last index of string 'to' : 18

Reference