ArrayList ensureCapacity() Method in Java with Examples

In Java, the ArrayList.ensureCapacity() method is used to increase the internal capacity of an ArrayList to ensure that it can hold a specified minimum number of elements. It helps to optimize performance by reducing the number of dynamic reallocations when adding a large number of elements.

Example 1: Here, we are using the ensureCapacity() method to preallocate space for an ArrayList of integers before adding elements.

[1, 2, 3, 4, 5]

Explanation: In the above example, we preallocate capacity for an ArrayList of integers before adding 5 elements to optimize memory usage.

Syntax of ensureCapacity() Method

public void ensureCapacity(int minCapacity)

Parameter: minCapacity: The minimum desired capacity for the ArrayList.

Other Examples of Java ArrayList.ensureCapacity()

Example 2: Here, we are using the ensureCapacity() method to preallocate space for a String ArrayList and to add elements.

[Ram, Shyam, Hari]

Explanation: In the above example, we preallocate capacity for an ArrayList of strings and then add a few names to the list.

Example 3: Here, we ensure capacity for an ArrayList when dealing with large data additions.

Size of an ArrayList: 200

Explanation: In the above example, we preallocate the capacity for an ArrayList to handle a large dataset of 200 elements.