Java StringBuilder ensureCapacity(int minimumCapacity) method ensures that the capacity is at least equal to the specified minimum. If the current capacity is less than the argument, then a new internal array is allocated with greater capacity. The new capacity is the larger of:

• The minimumCapacity argument.
• Twice the old capacity, plus 2.

Java StringBuilder ensureCapacity() Method Example

Example to ensure the capacity of string buffer using ensureCapacity() method.

public class EnsureCapacityExample {
    public static void main(String[] args) {
        StringBuilder builder = new StringBuilder();
        builder.ensureCapacity(11);
        System.out.println(builder.capacity());
    }
}

Output:

16

Reference

https://www.javaguides.net/2018/08/java-stringbuilder-class-api-guide.html