In this post, you will learn to create a Singleton class in Java. Let’s first see what Singleton class is. What is a Singleton class in Java? A Singleton class in Java is a class that can have only one object at a time. Singleton’s purpose is to control object creation. We can ensure that only one…
Read More Create a Singleton class in JavaIn 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 the…
Read More Sort ArrayList in descending order in JavaWant to learn how to count character occurrences in Java String? Below is the program that uses a Map to store chars as keys and the number of occurrences as values. class Test { public static void main(String[] args) { String str = “moiujjmhrqdoasdsooqavvae”; Map<Character, Integer> map = new HashMap<>(); for (int i = 0;…
Read More Count Character occurrences in Java StringThere are multiple ways to convert a String to an array in Java. We can convert it to a char array or String array. Convert a String to a char Array The String class, a fundamental data type in Java, has the useful toCharArray() method that enables the conversion of a String to a char array.…
Read More Convert a String to an Array in JavaIn this post, you will learn to check if a String contains only digits in Java. We will cover two methods: Using the Character.isDigit() method Using the Integer.parseInt() method Check if a String contains only digits in Java using the Character.isDigit() method In this example, we use a for loop to iterate over the elements…
Read More Check if a String contains only digits in JavaWe 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 the…
Read More Compare two ArrayList in JavaIn this tutorial, you will learn how to convert ArrayList to an Array in Java using two methods: Using a for loop – I will show you how to use a ‘for loop’ to go through an ArrayList and move everything over to an Array. It’s like packing your things into a new suitcase one item at a…
Read More Convert ArrayList to Array in JavaThere are multiple ways we can read a file in Java. We can always do that using the good old classes such as FileReader, BufferedReader, or Scanner class. However, in this lesson, we will explore other ways/libraries that make reading a file easier, and we are not required to write a lot of code. We will…
Read More How to Read a File in JavaThere are many ways to copy an array in Java. Here, we will explore the following: Using the clone() method Using System.arraycopy() Using the Arrays.copyOf() Copy an array in Java using the clone() method This is the most used way of cloning objects. The clone() method belongs to Object class, and we can use it to…
Read More Copy an Array in JavaWe often need to convert a list to a map in Java. In this lesson, you will learn how to do that with Java 8. If you are looking for more information on working with maps in Java, check out our tutorial on Map in Java. Let’s say we have a list of User objects. …
Read More Convert List to Map in Javapublic class Test { public static void main(String[] args) { Integer[] array = new Integer[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; // reverse an array Integer[] reversedArray = reverse(array); // print the elements Arrays.stream(reversedArray).forEach(item -> System.out.print(item + ” “)); } public static Integer[] reverse(Integer[] array) { List arrayList = Arrays.asList(array); Collections.reverse(arrayList); return…
Read More Reverse an Array in Javapublic class Test {z public static void main(String[] args) { List<Integer> numbers = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)); Collections.reverse(numbers); System.out.println(numbers); } } Output: [10, 9, 8, 7, 6, 5, 4, 3, 2, 1] Reverse a List using List.add() and List.remove() methods public class Test { public static void main(String[]…
Read More Reverse a List in Javaimport 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…
Read More Remove Duplicates from a List in Javaimport java.util.*; public class Test { public static void main(String[] args) { List<Integer> numbers = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)); System.out.println(numbers.stream().mapToInt(Integer::intValue).average().getAsDouble()); } } Output: 5.5 Here, we used the mapToInt(Integer::intValue) to convert the Stream<Integer> which is the result of the stream() method, to IntStream. import java.util.*; public class…
Read More Find the Average of Numbers in Java