Java ArrayList toArray() usage and example

Java ArrayList Methods

The Java ArrayList toArray() method converts an ArrayList to an array and returns it.

The syntax of toArray() method

arraylist.toArray(T[] arr)

toArray() parameter

• T [] arr(Optional)- Array used to store ArrayList elements

Note：Here, T specifies the type of the array.

toArray() return value

• 　If the method is passed an array T[]arr, it returns an array of type T
  

• If no parameters are passed, it returns an array of type Object

Example1：The toArray() method of ArrayList with parameters

import java.util.ArrayList;
class Main {
　　public static void main(String[] args) {
　　　　ArrayList<String> languages = new ArrayList<>();
　　　　//Add elements to the ArrayList
　　　　languages.add("Java");
　　　　languages.add("Python");
　　　　languages.add("C");
　　　　System.out.println("ArrayList: ")}　+　languages);
　　　　//Create a new String type array
　　　　//The size of the array is the same as the ArrayList
　　　　String[] arr = new String[languages.size()];
　　　　//Convert ArrayList to Array
　　　　languages.toArray(arr);
　　　　//Print all elements of the array
　　　　System.out.print("Array: ");
　　　　for(String item:arr) {
　　　　　　System.out.print(item+", ");
　　　　}
　　}
}

Output Result

ArrayList: [Java, Python, C]
Array: Java, Python, C,

In the above example, we created an ArrayList named languages. Note this line,

languages.toArray(arr);

Here, we pass a String type array as a parameter. Therefore, all elements of the ArrayList are stored in the array.

Note：The size of the array passed as a parameter should be equal to or greater than the ArrayList. Therefore, we useArrayList size()method is used to create an array of the same size as the ArrayList.

Example2：The toArray() method of ArrayList without parameters

import java.util.ArrayList;
class Main {
　　public static void main(String[] args) {
　　　　ArrayList<String> languages = new ArrayList<>();
　　　　//Add elements to the ArrayList
　　　　languages.add("Java");
　　　　languages.add("Python");
　　　　languages.add("C");
　　　　System.out.println("ArrayList: ")}　+　languages);
　　　　//Convert ArrayList to Array
　　　　//The method has no parameters
　　　　Object[] obj = languages.toArray();
　　　　//Print all elements of the array
　　　　System.out.print("Array: ");
　　　　for(Object item : obj) {
　　　　　　System.out.print(item+", ");
　　　　}
　　}
}

Output Result

ArrayList: [Java, Python, C]
Array: Java, Python, C,

In the above example, we used the toArray() method to convert an ArrayList to an array. Here, this method does not include optional parameters. Therefore, it will return an object array.

Note: It is recommended to use the toArray() method with parameters.

Java ArrayList Methods