How to Convert an array to ArrayList in java

In the last tutorial, you learned how to convert an ArrayList to Array in Java. In this guide, you will learn how to convert an array to ArrayList.

Method 1: Conversion using Arrays.asList()

Syntax:

ArrayList<T> arraylist= new ArrayList<T>(Arrays.asList(arrayname));

Example:
In this example, we are using Arrays.asList() method to convert an Array to ArrayList.

Here, we have an array cityNames with four elements. We have converted this array to an ArrayList cityList. After conversion, this arraylist has four elements, we have added two more elements to it using add() method.

In the end of the program, we are printing the elements of the ArrayList, which displays 6 elements, four elements that were added to arraylist from array and 2 new elements that are added using add() method.

import java.util.*;
public class JavaExample {
  public static void main(String[] args) {

    // Array declaration and initialization
    String cityNames[]={"Agra", "Mysore", "Chandigarh", "Bhopal"};

    // Array to ArrayList conversion
    ArrayList<String> cityList= new ArrayList<String>(Arrays.asList(cityNames));

    // Adding new elements to the list after conversion
    cityList.add("Chennai");
    cityList.add("Delhi");

    //print ArrayList elements using advanced for loop
    for (String str: cityList)
    {
      System.out.println(str);
    }
  }
}

Output:

Agra
Mysore
Chandigarh
Bhopal
Chennai
Delhi

Method 2: Conversion using Collections.addAll() method

Collections.addAll() method adds all the array elements to the specified collection. We can call the Collections.addAll method as shown below. It works just like Arrays.asList() method however, it is much faster. Conversion using Collections.addAll() method gives better performance compared to asList() method.

 String array[]={new Item(1), new Item(2), new Item(3), new Item(4)};
ArrayList<T> arraylist = new ArrayList<T>();
Collections.addAll(arraylist, array);

OR

Collections.addAll(arraylist, new Item(1), new Item(2), new Item(3), new Item(4));

Example:

import java.util.*;
public class JavaExample {
  public static void main(String[] args) {

    // Array declaration and initialization*/
    String array[]={"Hi", "Hello", "Howdy", "Bye"};

    //ArrayList declaration
    ArrayList<String> arraylist= new ArrayList<String>();

    // conversion using addAll()
    Collections.addAll(arraylist, array);

    //Adding new elements to the converted List
    arraylist.add("String1");
    arraylist.add("String2");

    //print ArrayList
    for (String str: arraylist)
    {
      System.out.println(str);
    }
  }
}

Output:

Hi
Hello
Howdy
Bye
String1
String2

Method 3: Convert Array to ArrayList manually

This program demonstrates how to convert an Array to ArrayList without using any predefined method such as asList() and addAll().
The logic of this program is pretty simple, we are iterating the array using for loop and adding the element to the ArrayList on every iteration of the loop. This means, in the first iteration, the first element of the array is added to the ArrayList, in the second iteration second element gets added and so on.

To read the whole array, we are using arr.length property. The array.length property returns the number of elements in the array. In the following example, since the array contains four elements, this will return 4. Thus we can say that the for loop runs from i=0 to i<4

In the end, we are displaying ArrayList elements using advanced for loop.

import java.util.*;
public class JavaExample {
  public static void main(String[] args) {

    //ArrayList declaration
    ArrayList<String> arrayList= new ArrayList<String>();

    //Initializing Array
    String array[] = {"Text1","Text2","Text3","Text4"};

    /* array.length returns the number of
     * elements present in array*/
    for(int i =0;i<array.length;i++)
    {

      //Adding array elements to the ArrayList
      arrayList.add(array[i]);
    }

    //print ArrayList content
    for(String str: arrayList)
    {
      System.out.println(str);
    }
  }
}

Output:

Text1
Text2
Text3
Text4

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