What is the difference between a process and a thread in Java?

This is the most frequently asked question during interviews. In this post we will discuss the differences between thread and process. You must have heard these terms while reading multithreading in java, both of these terms are related to each other. Both processes and threads are independent sequences of execution. The main difference is that threads (of the same process) run in a shared memory space, while processes run in separate memory spaces. Lets see the differences in detail:

Thread vs Process

1) A program in execution is often referred as process. A thread is a subset(part) of the process.

2) A process consists of multiple threads. A thread is a smallest part of the process that can execute concurrently with other parts(threads) of the process.

3) A process is sometime referred as task. A thread is often referred as lightweight process.

4) A process has its own address space. A thread uses the process’s address space and share it with the other threads of that process.

5)

Per process items             | Per thread items
------------------------------|-----------------
Address space                 | Program counter
Global variables              | Registers
Open files                    | Stack
Child processes               | State
Pending alarms                |
Signals and signal handlers   |
Accounting information        |

6) A thread can communicate with other thread (of the same process) directly by using methods like wait(), notify(), notifyAll(). A process can communicate with other process by using inter-process communication.

7) New threads are easily created. However the creation of new processes require duplication of the parent process.

8) Threads have control over the other threads of the same process. A process does not have control over the sibling process, it has control over its child processes only.