Java has multiple threads but only one Thread class

We can talk about thread with a lower-case ‘t’ and Thread with a capital ‘T’. When you see thread, we’re talking about a separate thread of execution. In other words, a separate call stack. When you see Thread, think of the Java naming convention. What, in Java, starts with a capital letter? Classes and interfaces. In this case, Thread is a class in the java.lang package. A Thread object represents a thread of execution; you’ll create an instance of class Thread each time you want to start up a new thread of execution.

A thread (lower-case ‘t’) is a separate thread of execution. That means a separate call stack. Every Java application starts up a main thread—the thread that puts the main() method on the bottom of the stack. The JVM is responsible for starting the main thread (and other threads, as it chooses, including the garbage collection thread). As a programmer, you can write code to start other threads of your own.