Java ensureCapacity(int minimumCapacity) Method
Last Updated : 23 Jul, 2025
In Java, the ensureCapacity(int minimumCapacity) method of the StringBuilder and StringBuffer classes is used to ensure that the buffer has a minimum capacity. If the current capacity is less than the specified minimum, it will increase the capacity to accommodate the required size.
Example 1: The below Java program demonstrates how the ensureCapacity() method makes sure there's enough space to hold a certain number of characters.
Java // Java program to demonstrate ensureCapacity() method public class Geeks { public static void main(String[] args) { // Create a StringBuilder object StringBuilder sb = new StringBuilder(); // Display the default capacity System.out.println("Default Capacity: " + sb.capacity()); // Ensure the capacity for 50 characters sb.ensureCapacity(50); System.out.println( "Capacity after ensuring space for 50 characters: " + sb.capacity()); } } OutputDefault Capacity: 16 Capacity after ensuring space for 50 characters: 50
Syntax of ensureCapacity() Method
void ensureCapacity(int minimumCapacity)
- Parameter: minimumCapacity: The minimum capacity that the buffer should have.
- Return Type: This method does not return any value; it modifies the capacity of the buffer.
Example 2: The below Java program demonstrates how the ensureCapacity() method increases the buffer capacity to ensure it can hold at least 30 characters.
Java // Java program to demonstrate ensureCapacity() // increasing capacity public class Geeks { public static void main(String[] args) { // Create a StringBuilder object StringBuilder sb = new StringBuilder(); // Display the default capacity System.out.println("Default Capacity: " + sb.capacity()); // Ensure the capacity for 30 characters sb.ensureCapacity(30); System.out.println( "Capacity after ensuring space for 30 characters: " + sb.capacity()); } } OutputDefault Capacity: 16 Capacity after ensuring space for 30 characters: 34
Example 3: The below Java program demonstrates how the ensureCapacity() ensures the buffer capacity is large enough to hold at least 100 characters.
Java // Java program to demonstrate ensureCapacity() // with larger size public class Geeks { public static void main(String[] args) { // Create a StringBuilder object StringBuilder sb = new StringBuilder(); // Ensure the capacity for 100 characters sb.ensureCapacity(100); System.out.println( "Capacity after ensuring space for 100 characters: " + sb.capacity()); } } OutputCapacity after ensuring space for 100 characters: 100
Example 4: The below Java program demonstrates how the ensureCapacity() ensure sufficient capacity for 50 characters while maintaining the existing content.
Java // Java program to demonstrate ensureCapacity() with content public class Geeks { public static void main(String[] args) { // Create a StringBuilder object StringBuilder sb = new StringBuilder("Hello"); // Display current capacity System.out.println("Current Capacity: " + sb.capacity()); // Ensure the capacity for 50 characters sb.ensureCapacity(50); System.out.println( "Capacity after ensuring space for 50 characters: " + sb.capacity()); } } OutputCurrent Capacity: 21 Capacity after ensuring space for 50 characters: 50
Example 5: The below Java program demonstrates how the ensureCapacity() ensure the buffer has enough capacity to hold at least 100 characters.
Java // Java program to demonstrate ensureCapacity() // with StringBuffer public class Geeks { public static void main(String[] args) { // Create a StringBuffer object StringBuffer sb = new StringBuffer(); // Display current capacity System.out.println("Current Capacity: " + sb.capacity()); // Ensure the capacity for 100 characters sb.ensureCapacity(100); System.out.println( "Capacity after ensuring space for 100 characters: " + sb.capacity()); } } OutputCurrent Capacity: 16 Capacity after ensuring space for 100 characters: 100
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