ArrayList trimToSize() Method in Java with Example

Last Updated : 10 Dec, 2024

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());
    }
}