1. What is java concurrency

1. What is Java Concurrency

·         Concurrency is the ability to run several programs or several parts of a program in parallel.

·         Concurrency enable a program to achieve high performance and throughput by utilizing the untapped capabilities of underlying operating system and machine hardware.

·         The backbone of java concurrency are threads.

·          A thread is a lightweight process which has its own call stack, but can access shared data of other threads in the same process.

·          A Java application runs by default in one process.

·         Within a Java application you can work with many threads to achieve parallel processing or concurrency.

2. Difference between parallel, sequential, concurrency execution

Sequential execution:

·         Multiple tasks executing one after one.

·         Second task will execute once first task will be finished.

·         Eg : Conducting a class by single faculty.

Parallel execution:

·         Executing multiple tasks at a time, without any dependency of another task.

·         Eg: Conducting a classes by different faculties.

Concurrency execution:

·         Executing multiple tasks at a time by pauses the currently executing task.

·         Eg: Conducting multiple classes by single faculty at a time.

3. Types of multitasking

·         Two types of multitasking.

Process based multitasking execution:

·         Executing multiple tasks simultaneously  where each task is separate independent program(process) is called as Process based multitasking.

·         Eg : Running a java program, listening a music, downloading a movie on same System CPU

·         Each task is running in a separate address of CPU

·         Above image shows , how OS is switch the multiple tasks, each process has its own address.

Thread based multitasking execution:

·         Executing multiple tasks concurrently where each task is separate independent part of same program is called as Thread based multitasking.

·         Here each task is a separate independent part of a single process, that part is called as thread.

·         Each Thread has its own stack area for its execution.

·         At a single instance of time JVM cannot execute two tasks at a time.

·         Above fig shows that, both threads are executed in suspend – resume fashion.