Java - Interview Questions and Answers on Thread States

Q1.  What is the initial state of a thread when it is created and started?

Ans. Ready state.

Q2.  What state does a thread enter when it terminates its processing?

Ans. When a thread terminates its processing, it enters the dead state.

Q3.  Explain Thread States ?


Runnable - waiting for its turn to be picked for execution by the thread schedular based on thread priorities.

Running - The processor is actively executing the thread code. It runs until it becomes blocked, or voluntarily gives up its turn. 

Waiting: A thread is in a blocked state while it waits for some external processing such as file I/O to finish.

Sleeping - Java threads are forcibly put to sleep (suspended) with Thread.sleep. they can resume using Thread.resume method.

Blocked on I/O - Will move to runnable after I/O condition like reading bytes of data etc changes.

Blocked on synchronization - Will move to Runnable when a lock is acquired.

Dead - The thread is finished working.

Q4.  Difference between yield() and sleeping()? 

Ans. When a task invokes yield(), it changes from running state to runnable state. When a task invokes sleep(), it changes from running state to waiting/sleeping state.