Static Methods and Static Blocks Static methods belong to the class and they will be loaded into memory along with the class; you can invoke them without creating an object. (using the class name as reference). Whereas a static block is a block of code with a static keyword. In general, these are used to initialize the static members. JVM executes static blocks before the main method at the time of class loading. Example The following example demonstrates the usage of static blocks and static methods in Java - public class Sample { ... Read More

When we are working with those Java applications that handle JSON data, it is common that we find different date formats. It might happen that one field contains just the date, while another includes time and date, and even time zone. For handling this type of data Jackson library is very helpful. Jackson is a popular Java library that is used to convert Java objects into JSON and vice versa. And this process is called serialization and deserialization. To handle multiple date formats in a single class, Jackson provides an annotation called @JsonFormat. The@JsonFormat The @JsonFormat annotation helps Jackson ... Read More

If you’ve been coding in Java for some time, you might have wondered why you can't make an enum extend another class. It seems like it should, but Java won't let you. Let's break down why this happens Enumeration in Java Enumeration (enum) in Java is a user-defined datatype which stores a set of constant values. You can use enumerations to store fixed values such as days in a week, months in a year, and seasons, etc. If we had to store all seven days of a week into one single variable then we might tend to use data ... Read More

A JAR file is like a ZIP file but for Java code. For the packaging of multiple class files, Java provides a file format known as JAR (Java Archive). Typically, a JAR file contains .class files, images, text files, and libraries in a single file that are required to execute the Java application or library. This file format is used to distribute application software and libraries in Java. All the predefined libraries are available in this format. If you have any library in JAR format, to use it in your application, you either need to place it in the current folder ... Read More

Java Virtual Machine is a program/software that runs Java applications. It takes Java bytecode (.class files) and converts the bytecode (line by line) into machine-understandable code, line by line so the processor can understand and execute it. JVM contains a module(components) known as a class loader. It is responsible for loading the program into memory and preparing it to run. Class Loader performs three main tasks - It Loads the class into the memory. ... Read More

In Java, both abstract and final are class modifiers but they are completely opposite to each other. That's why Java class cannot be both abstract and final. Abstract class An abstract class in Java is a class that may contain both abstract methods (without implementation) and concrete methods (with implementation). If a class has even one abstract method, it must be declared abstract. You cannot create objects of an abstract class directly. If you want to use the concrete method in an abstract class you need to inherit the class, provide implementation to the abstract methods (if any) and ... Read More

In general, while reading or writing data to a file, you can do so, from the start of the file. You cannot read/write from random position. The java.io.RandomAccessFile class in Java enables you to read/write data to a random-access file. This acts similar to a large array of bytes where the cursor known as file pointer works like an index. With the help of file pointer you can get the position of this pointer using the getFilePointer() method and set it using the seek() method. RandomAccessFile Class: Reading Files This class provides various methods to read and write data ... Read More

Once you write a Java program you need to compile it using the javac command, this shows you the compile time errors occurred (if any).Once you resolve them and compile your program success fully, an executable file with the same name as your class name is generated in your current folder, with the .class extension.Then you need to execute it using the java command as −java class_nameWhile executing, when JVM does not find a .class file with the specified name then a run time error occurs saying “Could not found or load main class” error as −D:\sample>java Example Error: Could ... Read More

The given task is to overwrite a line in a .txt file with new content. Assume we have a .txt file with the following content - Line 1: Hello World Line 2: This is a test file. Line 3: This line will be overwritten. Line 4: Goodbye! We want to overwrite line 3 with "This line has been changed". Following will be the resultant content - line 1: Hello World line 2: This is a test file. line 3: This line has been changed. line 4: Goodbye! Overwriting a Line in a ".txt" File There are no direct methods ... Read More

The split() method of the String class. splits the current string around matches of the given regular expression. The array returned by this method contains each substring of this string that is terminated by another substring that matches the given expression or is terminated by the end of the string.The replaceAll() method of the String class accepts two strings representing a regular expression and a replacement String and replaces the matched values with given String.To replace all the characters in of a file with '#' except a particular word (one way) −Read the contents of a file to a String.Create ... Read More