How to convert listing to array inwards Java together with vice-versa

There is no slow agency to convert an array to listing inward Java, but you lot tin forcefulness out easily convert a listing into array yesteryear calling toArray() method, which List inherit from Collection interface. If you lot exclusively rely on nub JDK, together with then only agency to convert an array to listing is looping over array together with populating listing ane chemical constituent at a time. But if you lot tin forcefulness out purpose opened upwardly rootage libraries similar Google Guava or Apache Commons lang together with then at that topographic point is many utility classes to convert listing to array together with vice-versa, equally shown inward this tutorial. If you lot are working on Java application, you lot volition oft take away to convert betwixt listing together with array. Influenza A virus subtype H5N1 listing is nil but a dynamic array which knows how to re-size itself when it gets amount or acquire around full. List uses charge cistron to create upwardly one's heed when to re-size, default value of its is 0.75. When they re-size, listing normally double their slots e.g. goes from xvi to 32 etc. You tin forcefulness out discovery these bully details inward their implementation classes e.g. ArrayList is ane of the pop listing inward Java which provides gild together with random access. BTW, if you lot desire to genuinely original Java Collection framework, together with then you lot must read Java Generics together with Collection book, written yesteryear Maurice Naftaline together with ane of the must read mass to acquire practiced on Java Collections framework.

Array to List inward Java

You tin forcefulness out purpose advanced for loop or classical for loop to loop over array together with add together each object into listing using add() method, this is non a bad approach together with you lot tin forcefulness out easily write your ain utility method tell ArrayUtils.toList() to encapsulate the logic. Though you lot take away to live on aware to render several overloaded methods for dissimilar types of array e.g. byte[], int[], short[], long[], float[], double[], char[], boolean[] and fifty-fifty object[]. This is cumbersome together with that's why its ameliorate to purpose mutual utility library similar Guava or Apache commons, which provides these kinds of handy method right from the box.

Here is how you lot convert an int array to List of integers inward Java :

 public static List<Integer> toIntegerList(int[] intArray) {         List<Integer> consequence = new ArrayList<>(intArray.length);          for (int i : intArray) {             result.add(i);         }          return result;     }

Similarly, you lot take away to write other listing conversion method to convert an array of boolean, byte, short, char, long, float, double or object into corresponding List inward Java.

List to Array inward Java

Converting a listing to an array is cakewalk, all you lot take away to create is telephone phone the toArray() method to acquire all items of a listing within an array. This method is overloaded too, the ane which doesn't conduct maintain whatever parameter render an Object[] but if you lot desire array of especial type, you lot tin forcefulness out purpose toArray(T[]) which returns all elements of array alongside the type you lot specified. It also returns elements inward the gild they are stored inward list. If array is non big plenty to shop all elements some other array alongside sufficient size is created together with returned. Just retrieve that, you lot cannot convert List to primitive array alongside this method, only agency to create this is iterating over List together with converting Integer to int using auto-boxing together with storing them into array.

Here is ane event of converting a List of String to an array of String inward Java :

List<String> movies = Arrays.asList("Captain America", "Avatar", "Harry Potter"); String[] arrayOfMovies = new String[movies.size()]; movies.toArray(arrayOfMovies);  System.out.println("list of String : " + movies); System.out.println("array of String : " + Arrays.toString(arrayOfMovies));  Output : list of String : [Captain America, Avatar, Harry Potter] array of String : [Captain America, Avatar, Harry Potter]

You tin forcefulness out come across that array also contains the String inward precisely same gild they were inward List.

Java Program to convert listing to array together with vice-versa

Here is our sample programme to demonstrate how to convert listing to array together with array to listing easily inward Java without using whatever 3rd political party library similar Apache Commons Collections or Google Guava.

package dto;  import java.util.ArrayList; import java.util.Arrays; import java.util.List;  /**  * Java programme to convert a listing to array together with vice-versa.  *   * @author WINDOWS 8  *  */ public class ListToArrayDemo {      public static void main(String args[]) {          // let's create a listing first         List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7);         System.out.println("list : " + numbers);          // let's get-go come across how slow it is to convert a listing to array         // simply telephone phone Collection.toArray() method          // You must exceed an Integer[], int[] volition non work         int[] ints = new int[numbers.size()];         // numbers.toArray(ints); // compile fourth dimension mistake expecting Integer[], got         // int[]          Integer[] integers = new Integer[numbers.size()];         numbers.toArray(integers);          System.out.println("array converted from listing : "                 + Arrays.toString(integers));          // at nowadays let's convert an array to a listing inward Java         String[] languages = { "Java", "Perl", "Lisp", "JavaScript", "Python" };          System.out.println("array : " + Arrays.toString(languages));          List<String> fromArray = new ArrayList<>(languages.length);          for (String str : languages) {             fromArray.add(str);         }          System.out.println("array to listing : " + fromArray);                           // You tin forcefulness out also create utility methods to convert array to list         // but you lot take away to create amount of nine method, much similar various         // println() method, ane for each primitive type together with ane for         // all form of object[]. I conduct maintain created 2 of them to         // demo you lot how to create them, let's come across how to purpose them         // now.                  List<String> names = toList(new String[]{"John", "Mohan", "Mary"});         System.out.println("list from array inward Java : " + names);                  List<Integer> primes = toIntegerList(new int[]{2, 3, 5, 7});         System.out.println("list of Integer from an array of int : " + primes);     }      /*      * Static utility method to convert int[] to List<Integer>      */     public static List<Integer> toIntegerList(int[] intArray) {         List<Integer> consequence = new ArrayList<>(intArray.length);          for (int i : intArray) {             result.add(i);         }          return result;     }      /*      * Static utility method to convert T[] to List<T> You tin forcefulness out purpose this method      * to convert whatever object[] to List<object.      */     public static <T> List<T> toList(T[] tArray) {         List<T> consequence = new ArrayList<>(tArray.length);          for (T object : tArray) {             result.add(object);         }          return result;     }  }  Output : listing : [1, 2, 3, 4, 5, 6, 7] array converted from listing : [1, 2, 3, 4, 5, 6, 7] array : [Java, Perl, Lisp, JavaScript, Python] array to listing : [Java, Perl, Lisp, JavaScript, Python] listing from array inward Java : [John, Mohan, Mary] listing of Integer from an array of int : [2, 3, 5, 7]

That's all close how to convert a listing to array together with vice-versa inward Java. Yes, at that topographic point is no similar a shot utility method e.g. toList(array) inward JDK API to convert an array to listing but its non hard to write one, only employment is that you lot take away to write nine overloaded methods to convert listing of 8 primitive type together with ane object array. Good matter is, converting listing to array is relatively slow alongside the assistance of Collection.toArray() method. Just retrieve to render right type of array equally autoboxing doesn't move alongside array. So if you lot desire to convert a List of Integer into array, brand certain you lot render an array of Integer e.g. new Integer[], array of primitive int volition non move e.g. new int[] volition give compile fourth dimension error.

Further Learning
Java Fundamentals: Collections
From Collections to Streams inward Java 8 Using Lambda Expressions
Grokking Algorithms yesteryear Aditya Bhargava
Java Programming Interview Exposed yesteryear Makham

If you lot similar this tutorial together with wants to larn to a greater extent than bout List interface from Java Collection framework, you lot tin forcefulness out also cheque out next tutorials :

• How to shuffle elements of listing inward Java? [example]
• How to sort listing inward Java? [solution]
• How to iterate over listing inward Java? [solution]
• What is departure betwixt List together with Set inward Java? [answer]
• How to convert Map to List inward Java? [answer]
• How to create together with initialize List inward ane line? [answer]
• How to convert List to Set inward Java? [example]

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