List of object array in Java
Java ArrayList
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Java ArrayListThe ArrayList class is a resizable array, which can be found in the java.util package. Show The difference between a built-in array and an ArrayList in Java, is that the size of an array cannot be modified (if you want to add or remove elements to/from an array, you have to create a new one). While elements can be added and removed from an ArrayList whenever you want. The syntax is also slightly different: ExampleCreate an ArrayList object called cars that will store strings: import java.util.ArrayList; // import the ArrayList class ArrayListIf you don't know what a package is, read our Java Packages Tutorial. Add ItemsThe ArrayList class has many useful methods. For example, to add elements to the ArrayList, use the add() method: Exampleimport java.util.ArrayList; public class Main { public static void main(String[] args) { ArrayListTry it Yourself » Access an ItemTo access an element in the ArrayList, use the get() method and refer to the index number: Examplecars.get(0);Try it Yourself » Remember: Array indexes start with 0: [0] is the first element. [1] is the second element, etc. Change an ItemTo modify an element, use the set() method and refer to the index number: Examplecars.set(0, "Opel");Try it Yourself » Remove an ItemTo remove an element, use the remove() method and refer to the index number: Examplecars.remove(0);Try it Yourself » To remove all the elements in the ArrayList, use the clear() method: Examplecars.clear();Try it Yourself » ArrayList SizeTo find out how many elements an ArrayList have, use the size method: Examplecars.size();Try it Yourself » Loop Through an ArrayListLoop through the elements of an ArrayList with a for loop, and use the size() method to specify how many times the loop should run: Examplepublic class Main { public static void main(String[] args) { ArrayListTry it Yourself » You can also loop through an ArrayList with the for-each loop: Examplepublic class Main { public static void main(String[] args) { ArrayListTry it Yourself » Other TypesElements in an ArrayList are actually objects. In the examples above, we created elements (objects) of type "String". Remember that a String in Java is an object (not a primitive type). To use other types, such as int, you must specify an equivalent wrapper class: Integer. For other primitive types, use: Boolean for boolean, Character for char, Double for double, etc: ExampleCreate an ArrayList to store numbers (add elements of type Integer): import java.util.ArrayList; public class Main { public static void main(String[] args) { ArrayListTry it Yourself » Sort an ArrayListAnother useful class in the java.util package is the Collections class, which include the sort() method for sorting lists alphabetically or numerically: ExampleSort an ArrayList of Strings: import java.util.ArrayList; import java.util.Collections; // Import the Collections class public class Main { public static void main(String[] args) { ArrayListTry it Yourself » ExampleSort an ArrayList of Integers: import java.util.ArrayList; import java.util.Collections; // Import the Collections class public class Main { public static void main(String[] args) { ArrayListTry it Yourself »
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