ArrayList trimToSize() Method in Java with Example

Last Updated : 11 Jul, 2025

In Java, the trimToSize() method is used to reduce the capacity of an ArrayList to match its current size. This helps to optimize memory usage when an ArrayList contains less elements than its allocated capacity.

Example 1: Here, we will use the trimToSize() method to trim an ArrayList of Strings.

Java

// Java program to demonstrate the use of  // trimToSize() method in ArrayList of Strings import java.util.ArrayList; public class GFG {  public static void main(String[] args) {    // Creating an ArrayList of Strings  ArrayList<String> n = new ArrayList<>(10);  // Adding elements to the ArrayList  n.add("Ram");  n.add("Shyam");  n.add("Hari");  // print the size and   // capacity before trimming  System.out.println("Size before trim: " + n.size());  System.out.println("Capacity before trim: Excess capacity exists");  // Trimming to the size   // of the ArrayList  n.trimToSize();  // Printing the size after trimming  System.out.println("Size after trim: " + n.size());  } }

Output

Size before trim: 3 Capacity before trim: Excess capacity exists Size after trim: 3

Syntax of trimToSize() Method

public void trimToSize()

Below is the diagram that represents the working of trimToSize() method of ArrayList.

Example 2: Here, we will use the trimToSize() method to trim an ArrayList of Integers.

Java

// Java program to demonstrate trimToSize()  // with Integer ArrayList import java.util.ArrayList; public class GFG {  public static void main(String[] args) {  // creating an Empty Integer ArrayList  ArrayList<Integer> arr = new ArrayList<Integer>(9);  arr.add(2);  arr.add(4);  arr.add(5);  arr.add(6);  arr.add(11);  // trims the size to the   // number of elements  arr.trimToSize();  System.out.println("The List elements are:");  // prints all the elements  for (Integer n : arr) {  System.out.println("Number:" + n);  }  } }

Output

The List elements are: Number:2 Number:4 Number:5 Number:6 Number:11

Example 3: Here, we will check the behavior of trimToSize() on an empty ArrayList.

Java

// Java program to show trimToSize()  // on an empty ArrayList import java.util.ArrayList; public class GFG {  public static void main(String[] args) {    // Creating an empty ArrayList  ArrayList<String> arr = new ArrayList<>();  // Trimming the capacity of   // an empty ArrayList  arr.trimToSize();  // Printing the size after trimming  System.out.println("Size of empty ArrayList after trim: " + arr.size());  } }