java lists

In this post, you will learn how to Serialize and Deserialize an ArrayList in Java using the FileOutputStream and FileInputStream classes. How to Serialize an ArrayList in Java? Serialization is the process of changing the state of an object into a byte stream. For example, we use it to write some Java objects into a file.…

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In one of the previous examples, we covered how to sort an ArrayList in ascending order. In this post, you will learn how to sort ArrayList in descending order in Java. We will explore the following ways: Using the sort() method Using the Collections.sort() and Collections.reverse() methods Sort ArrayList in descending order in Java using…

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We often need to compare two ArrayList in Java. In this post, you will learn how to do that in two ways: Using the ArrayList.equals() method Using the CollectionUtils.isEqualCollection() method Compare two ArrayList in Java using the ArrayList.equals() method The ArrayList.equals() method compares two ArrayList. It compares the sizes of the lists, elements equality, and…

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In this lesson, you will learn how to convert a JSON array to a Java list. We will use the ObjectMapper class from the Jackson library. Let’s say we have a JSON that is an array of objects: [ { “name”:”John”, “grade”:8, “city”:”Boston” }, { “name”:”Tom”, “grade”:9, “city”:”Denver” }, { “name”:”Megan”, “grade”:8, “city”:”New York city”…

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public Object get(int index); import java.util.*; public class Test { public static void main(String[] args) { List<String> cities = new ArrayList<>(Arrays.asList(“New York”, “London”, “Paris”, “Chicago”, “Rome”)); // retrieve the second element from the list System.out.println(cities.get(2)); // retrieve the 4th element from the list System.out.println(cities.get(4)); } } Output: Paris Rome   Lists are zero-based indexes, which means that the…

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import java.util.*; public class Test { public static void main(String[] args) { List<String> names = new ArrayList<>(Arrays.asList(“Megan”, “Tom”, “Steve”, “Megan”, “Meliisa”, “Tom”, “John”)); Set<String> uniqueNames = new HashSet<>(names); // creating a Set from the List System.out.println(uniqueNames); } } Output: [Megan, Tom, Steve, John, Meliisa] Remove duplicates from a List in Java using the Java 8…

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import java.util.*; public class Test { public static void main(String[] args) { List<Integer> numbers = new ArrayList<>(Arrays.asList(7, 12, 5, 28, 97, 14, 2, 7, 8, 12, 19, 22)); Collections.sort(numbers); System.out.println(numbers); } } Output: [2, 5, 7, 7, 8, 12, 12, 14, 19, 22, 28, 97] Using the sort() method from ArrayList class public class Test…

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public class Test { public static void main(String[] args) { List<Integer> list = new ArrayList<>(Arrays.asList(7, 19, 14, 1, 12, 22, 18, 3, 28, 5)); System.out.println(“Maximum value: ” + Collections.max(list)); System.out.println(“Minimum value: ” + Collections.min(list)); } } Output: Maximum value: 28 Minimum value: 1 Finding the maximum and minimum values in List using the Java 8…

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LinkedList<String> list = new LinkedList<>(); List<Integer> list = new LinkedList<>(); class Test { public static void main(String[] args) { List<String> list = new LinkedList<>(); list.add(“Steve”); list.add(“Megan”); list.add(“Melissa”); list.add(“Ryan”); System.out.println(list); } } Output: [Steve, Megan, Melissa, Ryan] class Test { public static void main(String[] args) { List<String> list = new LinkedList<>(); list.add(“Steve”); list.add(“Megan”); list.add(“Melissa”); list.add(“Ryan”); List<String>…

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ArrayList<String> list = new ArrayList<>(); List<Integer> list = new ArrayList<>(); class Test { public static void main(String[] args) { List<String> list = new ArrayList<>(); list.add(“Steve”); list.add(“Megan”); list.add(“Melissa”); list.add(“Ryan”); System.out.println(list); } } Output: [Steve, Megan, Melissa, Ryan]   Using the addAll() method, we can add all the elements of an existing list to the newly created…

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