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Java ArrayList ensureCapacity() Method

❮ ArrayList Methods


Example

Increase the capacity of a list to 15 items:

import java.util.ArrayList;

public class Main {
  public static void main(String[] args) {
    ArrayList<Integer> list = new ArrayList<Integer>();
    list.ensureCapacity(15);
    for (int i = 1; i <= 15; i++) {
      list.add(i);
    }
    System.out.println(list);
  }
}

Try it Yourself »


Definition and Usage

The ensureCapacity() method increases the capacity of a list to a specified amount, if necessary.

This method does not have a visible effect but it can make code more efficient.

When methods such as add() and addAll() are called, if the capacity of a list is not large enough then some extra work is done to add enough space for the new items. It takes a bit of time to do this, so having this happen with every add() call is not ideal.

If you know approximately how many items you are going to add, the ensureCapacity() method allows you to increase the capacity of the list just once for multiple add() calls.


Syntax

public void add(int capacity)

Parameter Values

Parameter Description
capacity Required. Specifies the number of items that the list should be able to hold.

Related Pages

Java Arrays Tutorial

Java ArrayList Tutorial


❮ ArrayList Methods
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