Initialize an ArrayList in Java |
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Initialize an ArrayList in Java
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ArrayList is a part of collection framework and is present in java.util package. It provides us dynamic arrays in Java. Though, it may be slower than standard arrays but can be helpful in programs where lots of manipulation in the array is needed. ArrayList inherits AbstractList class and implements List interface. ArrayList is initialized by a size, however the size can increase if collection grows or shrink if objects are removed from the collection. Java ArrayList allows us to randomly access the list. ArrayList can not be used for primitive types, like int, char, etc. We need a wrapper class for such cases (see this for details). ArrayList in Java can be seen as similar to vector in C++.
// Java code to illustrate initialization // of ArrayList using add() method import java.util.*; public class GFG { public static void main(String args[]) { // create a ArrayList String type ArrayList gfg = new ArrayList(); // Initialize an ArrayList with add() gfg.add("Geeks"); gfg.add("for"); gfg.add("Geeks"); // print ArrayList System.out.println("ArrayList : " + gfg); } } Output: ArrayList : [Geeks, for, Geeks] Examples: Using shorthand version of this method Java
// Java code to illustrate initialization // of ArrayList using add() method import java.util.*; public class GFG { public static void main(String args[]) { // create a ArrayList String type // and Initialize an ArrayList with add() ArrayList gfg = new ArrayList() { { add("Geeks"); add("for"); add("Geeks"); } }; // print ArrayList System.out.println("ArrayList : " + gfg); } } Output: ArrayList : [Geeks, for, Geeks] Initialization using asList() Syntax: ArrayList obj = new ArrayList( Arrays.asList(Obj A, Obj B, Obj C, ....so on)); Examples: Java
// Java code to illustrate initialization // of ArrayList using asList method import java.util.*; public class GFG { public static void main(String args[]) { // create a ArrayList String type // and Initialize an ArrayList with asList() ArrayList gfg = new ArrayList( Arrays.asList("Geeks", "for", "Geeks")); // print ArrayList System.out.println("ArrayList : " + gfg); } } Output: ArrayList : [Geeks, for, Geeks] Initialization using List.of() method Syntax: List obj = new ArrayList( List.of(Obj A, Obj B, Obj C, ....so on)); Examples: Java
// Java code to illustrate initialization // of ArrayList using List.of() method import java.util.*; public class GFG { public static void main(String args[]) { // create a ArrayList String type // and Initialize an ArrayList with List.of() List gfg = new ArrayList( List.of("Geeks", "for", "Geeks")); // print ArrayList System.out.println("ArrayList : " + gfg); } } Output: ArrayList : [Geeks, for, Geeks] Initialization using another Collection Syntax: List gfg = new ArrayList(collection); Examples: Java
// Java code to illustrate initialization // of ArrayList using another collection import java.util.*; public class GFG { public static void main(String args[]) { // create another collection List arr = new ArrayList(); arr.add(1); arr.add(2); arr.add(3); arr.add(4); arr.add(5); // create a ArrayList Integer type // and Initialize an ArrayList with arr List gfg = new ArrayList(arr); // print ArrayList System.out.println("ArrayList : " + gfg); } } Output: ArrayList : [1, 2, 3, 4, 5] Initialization using stream() and collect() methods 1. Syntax: ArrayList listName = Stream.of(element1, element2, ..., elementN).collect(Collectors.toCollection(ArrayList::new));1. Examples: Java
import java.util.ArrayList; import java.util.stream.Collectors; import java.util.stream.Stream; public class GFG { public static void main(String args[]) { // create a stream of elements using Stream.of() // method collect the stream elements into an // ArrayList using the collect() method and // Collectors.toCollection() method ArrayList list = Stream.of("Geeks", "For", "Geeks") .collect(Collectors.toCollection( ArrayList::new)); System.out.println(list); // print the ArrayList } } Output [Geeks, For, Geeks] R Rajput-Ji Improve Next Article How to Initialize an Array in Java? Please Login to comment... |
Below are the various methods to initialize an ArrayList in Java:【本文地址】