Convert ArrayList to Array in Java

In this post we’ll see how to convert ArrayList to array in Java. Since internal implementation of ArrayList uses an array internally to store its element so ArrayList class itself provides toArray() method to convert ArrayList to array. There are two overloaded toArray() methods.

  • toArray()– Returns an array containing all of the elements in this list in proper sequence. The returned array will be “safe” in that no references to it are maintained by this list. Returned array is of type Object.
  • toArray(T[] a)– Returns an array containing all of the elements in this list in proper sequence. The runtime type of the returned array is that of the specified array.

Though one problem with using these methods to convert ArrayList to array in Java is that the reference of the stored objects are shared between both ArrayList and converted array. Any modification to any stored object will be reflected in other data structure too.

Another option is to do the conversion manually without using any method. See example.

First we’ll see an example of toArray() method where conversion of ArrayList to array and then reflected modification is shown. For that we’ll have to store custom objects in ArrayList so here is a class whose objects are stored in ArrayList.

public class Employee{
	private int empId;
  private String empName;
  private int age;
  Employee(int empId, String empName, int age){
    this.empId = empId;
    this.empName = empName;
    this.age = age;
  }
  public int getEmpId() {
    return empId;
  }
  public void setEmpId(int empId) {
    this.empId = empId;
  }
  public String getEmpName() {
    return empName;
  }
  public void setEmpName(String empName) {
    this.empName = empName;
  }
  public int getAge() {
    return age;
  }
  public void setAge(int age) {
    this.age = age;
  }
    
  @Override
  public String toString() {    
    return getEmpId() + " " + getEmpName() + " " + getAge();
  }
}

Using toArray(T[] a) method to convert ArrayList to array

Here we have an ArrayList storing objects of type Employee. Then this ArrayList is converted to array. Then an object in ArrayList is modified, same way an object is modified in array. As you can see both the changes are reflected in both ArrayList as well as array.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class ListToArray {
  public static void main(String[] args) {
    List<Employee> empList = new ArrayList<Employee>();
    empList.add(new Employee(1, "Zhiang", 34));
    empList.add(new Employee(2, "Marie", 23));
    empList.add(new Employee(3, "Amy", 31));
    empList.add(new Employee(4, "Robbie", 45));
    // creating array of same size as list
    Employee[] empArr = new Employee[empList.size()];
    // Converting ArrayList to array   
    empArr = empList.toArray(empArr);
        
    System.out.println("Employees- " + Arrays.toString(empArr));
            
    empList.get(3).setEmpName("Jack");
    empArr[1].setAge(45);
    System.out.println("After modifications");
    System.out.println("List elements-- " + empList);
    System.out.println("Employees- " + Arrays.toString(empArr));
  }
}

Output

Employees- [1 Zhiang 34, 2 Marie 23, 3 Amy 31, 4 Robbie 45]
After modifications
List elements-- [1 Zhiang 34, 2 Marie 45, 3 Amy 31, 4 Jack 45]
Employees- [1 Zhiang 34, 2 Marie 45, 3 Amy 31, 4 Jack 45]

Using toArray() method to convert ArrayList to array

import java.util.ArrayList;
import java.util.List;

public class ListToArray {
  public static void main(String[] args) {
    List<String> carList = new ArrayList<String>();
    carList.add("Audi");
    carList.add("Jaguar");
    carList.add("BMW");
    carList.add("Mini Cooper");
    Object[] carArr = carList.toArray();
    for(Object car : carArr) {
      System.out.println("Car- " + car);
    }
  }
}

As you can see the converted array is of type Object which is a drawback of using this method.

Converting ArrayList to array without any API methods

You can also convert ArrayList to array in Java by iterating the ArrayList and then assigning elements to array.

public class ListToArray {
  public static void main(String[] args) {
    List<String> carList = new ArrayList<String>();
    carList.add("Audi");
    carList.add("Jaguar");
    carList.add("BMW");
    carList.add("Mini Cooper");
    // creating array of same size as list
    String[] carArr = new String[carList.size()];

    // iterate list and assign values to array
    for(int i =0; i < carList.size(); i++){
      carArr[i] = carList.get(i);
    }      
    System.out.println("Cars- " + Arrays.toString(carArr));        
  }
}

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