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.
// Java program to demonstrate the use of ensureCapacity()
// method with an ArrayList of Integers
import java.util.ArrayList;
public class GFG {
public static void main(String[] args) {
// create an ArrayList of Integers
ArrayList<Integer> l = new ArrayList<>();
// preallocate capacity for 5 elements
l.ensureCapacity(5);
// Add elements to the ArrayList
for (int i = 1; i <= 5; i++) {
l.add(i);
}
System.out.println(l);
}
}
Output
[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.
// Java program to demonstrate the use of ensureCapacity()
// method with an ArrayList of Strings
import java.util.ArrayList;
public class GFG {
public static void main(String[] args) {
// Create an ArrayList of Strings
ArrayList<String> n = new ArrayList<>();
// Preallocate capacity for 7 elements
n.ensureCapacity(7);
// Add elements to the ArrayList
n.add("Ram");
n.add("Shyam");
n.add("Hari");
System.out.println(n);
}
}
Output
[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.
// Java program to demonstrate the use of ensureCapacity()
// with a large dataset
import java.util.ArrayList;
public class GFG {
public static void main(String[] args) {
// Create an ArrayList of Integers
ArrayList<Integer> l = new ArrayList<>();
// Preallocate capacity for 200 elements
l.ensureCapacity(200);
// Add 200 elements to the ArrayList
for (int i = 1; i <= 200; i++) {
l.add(i);
}
System.out.println("Size of an ArrayList: " + l.size());
}
}
Output
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.