ArrayList ensureCapacity() method in Java with Examples

The ensureCapacity() method of java.util.ArrayList class increases the capacity of this ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.

Syntax:

public void ensureCapacity(int minCapacity)

Parameters: This method takes the desired minimum capacity as a parameter.

Below are the examples to illustrate the ensureCapacity() method.

Example 1:

// Java program to demonstrate
// ensureCapacity() method for Integer value

import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        try {

            // Creating object of ArrayList<Integer>
            ArrayList<Integer>
                arrlist = new ArrayList<Integer>();

            // adding element to arrlist
            arrlist.add(10);
            arrlist.add(20);
            arrlist.add(30);
            arrlist.add(40);

            // Print the ArrayList
            System.out.println("ArrayList: "
                               + arrlist);

            // ensure that the ArrayList
            // can hold upto 5000 elements
            // using ensureCapacity() method
            arrlist.ensureCapacity(5000);

            // Print
            System.out.println("ArrayList can now"
                               + " surely store upto"
                               + " 5000 elements.");
        }

        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

ArrayList: [10, 20, 30, 40]
ArrayList can now surely store upto 5000 elements.

Example 2:

// Java program to demonstrate
// ensureCapacity() method for String value

import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        try {

            // Creating object of ArrayList<Integer>
            ArrayList<String>
                arrlist = new ArrayList<String>();

            // adding element to arrlist
            arrlist.add("A");
            arrlist.add("B");
            arrlist.add("C");
            arrlist.add("D");

            // Print the ArrayList
            System.out.println("ArrayList: "
                               + arrlist);

            // ensure that the ArrayList
            // can hold upto 400 elements
            // using ensureCapacity() method
            arrlist.ensureCapacity(400);

            // Print
            System.out.println("ArrayList can now"
                               + " surely store upto"
                               + " 400 elements.");
        }

        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

ArrayList: [A, B, C, D]
ArrayList can now surely store upto 400 elements.