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 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 JavaIn this lesson, you will learn how to iterate over JsonNode in Java. JsonNode class is the base class for all JSON nodes, which form the basis of Jackson’s JSON Tree Model. How to iterate over JsonNode in Java? To loop through the JsonNode, we need to use the Java Iterator interface. Here is an example program…
Read More Iterate over JsonNode in JavaIn the previous lessons, we covered converting a Java Object to JsonNode and vice versa. Here, you will see how to modify JsonNode with the Java Jackson library. To see where to find Jackson jars, read Introduction to Java JSON. How to modify JsonNode with Java Jackson? The JsonNode class is immutable. That means we cannot modify it.…
Read More Modify JsonNode with Java JacksonIn the previous lesson, you learned how to ignore unknown fields, and now you will see how to ignore null fields with Java Jackson. We use the Jackson library in all the lessons since it is one of the most widely used Java library for working with JSON. To see where to find Jackson jars,…
Read More Ignore null fields with Java JacksonJackson is a popular Java library that provides powerful tools for converting JSON objects to Java objects and vice versa. In this tutorial, we will explore the different ways of mapping JSON objects to Java objects using Jackson. We’ll also look at how to handle dynamic JSON objects and cover some useful Jackson annotations that…
Read More Master Mapping JSON Objects to Java Objects with JacksonIn the previous lesson, we covered converting Java Object to JSON. Here, you will learn how to convert JSON to Java Object using the ObjectMapper class from the Jackson library. How to convert JSON to Java Object? We will use the readValue() method from the ObjectMapper class. There are a few overloaded readValue() methods. We will use the one that accepts…
Read More Convert JSON to Java ObjectSometimes we need to consume HTTPS endpoints that do not have valid certificates. We can do that by configuring the Java HttpClient to accept all SSL certificates, even from an untrusted Certificate Authority. Here you will see how to communicate with HTTPS endpoint that may not have a valid SSL certificate. In the following example,…
Read More Java HttpClient – Accept all SSL Certificates