What is user-defined class in Java

In Java, predefined methods are the method that is already defined in the Java class libraries is known as predefined methods. It is also known as the standard library method or built-in method. We can directly use these methods just by calling them in the program at any point.

Runtime class in Java. Every Java application has a single instance of class Runtime that allows the application to interface with the environment in which the application is running. The current runtime can be obtained from the getRuntime method.

Predefined Classes in Java. The library of predefined class in Java is called Java class library or application programming interface (API) . In Java, classes are organized into groups called packages. Each package has a specific name such as java.