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StringBuilder capacity() Method in Java

Last Updated : 11 Jul, 2025
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In Java, the capacity() method of StringBuilder Class is used to return the current capacity of StringBuilder object. The capacity is the amount of storage available to insert new characters.

Example 1: Here, we use the capacity() method to check the current capacity of the StringBuilder object.

Java 
// Java program to demonstrate
// the capacity() Method in StringBuilder
class Geeks {
    public static void main(String[] args) {

        // create a StringBuilder object,
        // default capacity will be 16
        StringBuilder sb = new StringBuilder();

        // get default capacity
        int c = sb.capacity();

        System.out.println("Default Capacity of StringBuilder: "
                + c);

        // add the String to StringBuilder Object
        sb.append("Geek");

        // get capacity
        c = sb.capacity();

        System.out.println("StringBuilder: " + sb);
        System.out.println("Current Capacity of StringBuilder: "
                + c);
    }
}

Output
Default Capacity of StringBuilder: 16
StringBuilder: Geek
Current Capacity of StringBuilder: 16

Syntax of StringBuilder capacity() Method

public int capacity()

Return Value: This method returns the current capacity of StringBuilder class.

Example 2: Here, we use the capacity() method with a String Passed as Parameter.

Java 
// Using capacity() Method with a String Passed as Parameter
class Geeks {
    public static void main(String[] args) {
      
        // create a StringBuilder object
        // with a String passed as parameter
        StringBuilder sb = new StringBuilder("WelcomeGeeks");

        // get capacity
        int c = sb.capacity();

        System.out.println("StringBuilder: " + sb);
        System.out.println("Capacity of StringBuilder: "
                           + c);
    }
}

Output
StringBuilder: WelcomeGeeks
Capacity of StringBuilder: 28


Example 3: Here, we use the capacity() method on a null StringBuilder object. This will throw a NullPointerException.

Java 
// Handling NullPointerException with 
// StringBuilder capacity()
import java.io.*;

class Geeks {
    public static void main(String[] args) {
      
        // Create a null StringBuilder object
        StringBuilder sb = null;
        try {
         
            int c = sb.capacity();
            System.out.println("Capacity: " + c);
        }
        catch (NullPointerException e) {
          
            // Handle the exception
            System.out.println(
                "Error: Cannot call capacity() on a null StringBuilder.");
        }
    }
}

Output
Error: Cannot call capacity() on a null StringBuilder.

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AmanSingh2210
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