Java ArrayList trimToSize() Method

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Description

The java.util.ArrayList.trimToSize() method trims the capacity of this ArrayList instance to be the list's current size. An application can use this operation to minimize the storage of an ArrayList instance.

Declaration

Following is the declaration for java.util.ArrayList.trimToSize() method

public void trimToSize()

Parameters

NA

Return Value

This method does not return any value.

Exception

NA

Example 1

The following example shows the usage of Java ArrayList trimToSize() method. We're adding couple of Integers to the ArrayList object using add() method calls per element. We're trimming the array size using trimToSize() methd and then print each element to show the elements added.

package com.tutorialspoint;
import java.util.ArrayList;
public class ArrayListDemo {
   public static void main(String[] args) {
      
      // create an empty array list 
      ArrayList<Integer> arrayList = new ArrayList<>();

      // use add() method to add elements in the arrayList
      arrayList.add(20);
      arrayList.add(30);
      arrayList.add(20);
      arrayList.add(30);
      arrayList.add(15);
      arrayList.add(22);
      arrayList.add(11);

      // trim the size of the arrayList
      arrayList.trimToSize();
	  
      // let us print all the elements available in arrayList
      for (Integer number : arrayList) {
         System.out.println("Number = " + number);
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Number = 20
Number = 30
Number = 20
Number = 30
Number = 15
Number = 22
Number = 11

Example 2

The following example shows the usage of Java ArrayList trimToSize() method. We're adding couple of Strings to the ArrayList object using add() method calls per element. We're trimming the array size using trimToSize() methd and then print each element to show the elements added.

package com.tutorialspoint;
import java.util.ArrayList;
public class ArrayListDemo {
   public static void main(String[] args) {
      
      // create an empty array list
      ArrayList<String> arrayList = new ArrayList<>();

      // use add() method to add elements in the arrayList
      arrayList.add("Welcome");
      arrayList.add("To");
      arrayList.add("Tutorialspoint");
      
      // trim the size of the arrayList
      arrayList.trimToSize();
      System.out.println("ArrayList = " + arrayList);      
   }
}

Output

Let us compile and run the above program, this will produce the following result −

ArrayList = [Welcome, To, Tutorialspoint]

Example 3

The following example shows the usage of Java ArrayList trimToSize(E) method. We're adding couple of Student objects to the ArrayList object using add() method calls per element. We're trimming the array size using trimToSize() methd and then print each element to show the elements added.

package com.tutorialspoint;
import java.util.ArrayList;
public class ArrayListDemo {
   public static void main(String[] args) {

      // create an empty arrayList
      ArrayList<Student> arrayList = new ArrayList<>();

      // use add() method to add elements in the arrayList
      arrayList.add(new Student(1, "Julie"));
      arrayList.add(new Student(2, "Robert"));
      arrayList.add(0, new Student(3, "Adam"));

      // trim the size of the arrayList
      arrayList.trimToSize();
      System.out.println("ArrayList = " + arrayList);      
   }
}
class Student {
   int rollNo;
   String name;
   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }
   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
}

Output

Let us compile and run the above program, this will produce the following result −

ArrayList = [[ 3, Adam ], [ 1, Julie ], [ 2, Robert ]]