The class loading mechanism in Java is a crucial part of the Java Virtual Machine (JVM) that dynamically loads classes into memory as needed. This process is managed by class loaders, which are special classes responsible for locating and loading class files. When a Java application is executed, the class loader finds the required classes and loads them on demand, ensuring that only the necessary classes are loaded into memory at any given time.

Java has three main types of built-in class loaders: the Bootstrap Class Loader, which loads core Java classes; the Extension Class Loader, which loads classes from the Java extension directories; and the Application Class Loader, which loads classes from the application’s classpath. These class loaders work in a hierarchical manner, where the JVM first attempts to load classes from the standard libraries before looking in application-specific locations.

In some cases, developers may need to create custom class loaders to extend or modify the default behavior. Custom class loaders can be implemented by extending the java.lang.ClassLoader class and overriding methods such as findClass and loadClass to customize how classes and resources are loaded ¹²⁵.