StringBuilder capacity() Method in Java

Last Updated : 11 Jul, 2025

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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