Overview of Threads

Process

A process is an instance of a computer program that is executed sequentially. It is a collection of instructions which are executed simultaneously at the rum time. Thus several processes may be associated with the same program. For example, to check the spelling is a single process in the Word Processor program and you can also use other processes like printing, formatting, drawing, etc. associated with this program.

Thread

A thread is a lightweight process which exist within a program and executed to perform a special task. Several threads of execution may be associated with a single process. Thus a process that has only one thread is referred to as a single-threaded process, while a process with multiple threads is referred to as a multi-threaded process.

In Java Programming language,  thread is a sequential path of code execution within a program. Each thread has its own local variables, program counter and lifetime. In single threaded runtime environment, operations are executes sequentially i.e. next operation can execute only when the previous one is complete. It exists in a common memory space and can share both data and code of a program. Threading concept is very important in Java through which we can increase the speed of any application. You can see diagram shown below in which a thread is executed along with its several operations with in a single process. 

Main Thread

When any standalone application is running, it firstly execute the main() method runs in a one thread, called the main thread. If no other threads are created by the main thread, then program terminates when the main() method complete its execution. The main thread creates some other threads called child threads. The main() method execution can finish, but the program will keep running until the all threads have complete its execution.