Multithreading in Java refers to the process of executing multiple threads simultaneously for maximum utilization of the CPU. A thread is a lightweight sub-process, the smallest unit of processing. Java supports multithreading through the Thread class, which allows us to create a lightweight process that executes some tasks. We can create multiple threads in our program and start them, and Java runtime will take care of creating machine-level instructions and work with the OS to execute them in parallel.

To create a thread, we can either extend the java.lang.Thread class or implement the java.lang.Runnable interface. When we extend the Thread class, we override the run() method available in the Thread class, and a thread begins its life inside the run() method. When we implement the Runnable interface, we override the run() method and instantiate a Thread object and call start() method on this object.

Multithreading in Java has several advantages, including saving time as we can perform multiple operations together, and threads are independent, so they dont block the user to perform multiple operations at the same time. Additionally, if an exception occurs in a single thread, it does not affect other threads.

The life cycle of a thread in Java has five states: New, Runnable, Running, Non-Runnable (Blocked), and Terminated. A thread goes through various stages in its life cycle, and this life cycle is controlled by the JVM.

In summary, multithreading in Java allows concurrent execution of two or more parts of a program for maximum utilization of CPU. Java supports multithreading through the Thread class, and we can create multiple threads in our program and start them. Multithreading has several advantages, including saving time and allowing multiple operations to be performed together. The life cycle of a thread in Java has five states.