ALL QUESTIONS RELATED TO THREAD

Java Thread Interview Questions (83–138) – Easy Answer Table

No	Question	Best Short Answer
83	What is Process?	A process is an independent program in execution having its own memory space.
84	What is Thread in Java?	A thread is a lightweight sub-process used for concurrent execution inside a program.
85	Process vs Thread	Process has separate memory; threads share same memory inside a process.
86	What is Multitasking?	Running multiple tasks simultaneously using CPU scheduling.
87	Types of Multitasking	Process-based multitasking and Thread-based multitasking.
88	Benefits of Multithreading	Improves performance, CPU utilization, responsiveness, and resource sharing.
89	Explain Thread in Java	A thread is the smallest unit of execution that runs independently inside a process.
90	Java API that supports threads	java.lang.Thread and java.lang.Runnable.
91	Main Thread	The main thread is the first thread created when a Java program starts.
92	Ways to create thread	Two ways: Extend Thread class or implement Runnable interface.
93	Creating thread using Runnable	Implement Runnable and override run() then pass object to Thread.
94	Creating thread using Thread class	Extend Thread class and override run() method.
95	Best approach for creating thread	Runnable interface because Java supports single inheritance.
96	Thread Scheduler	JVM component that decides which thread executes next.
97	Thread Life Cycle	New → Runnable → Running → Waiting/Blocked → Dead.
98	Restart dead thread	No, once a thread is dead it cannot be restarted.
99	Can one thread block another?	Yes, when threads compete for the same resource or lock.
100	Restart already started thread	No, calling start() again throws IllegalThreadStateException.
101	If run() not overridden	Thread will execute empty run() from Thread class.
102	Overload run() method	Yes possible, but JVM only calls run() with no parameters.
105	What is Lock	Lock controls access of multiple threads to shared resources.
106	Ways to do synchronization	Synchronized method, synchronized block, static synchronization.
107	Synchronized method	A method declared with synchronized allowing one thread at a time.
108	When to use synchronized	When multiple threads access shared data.
109	Can other threads execute synchronized methods simultaneously	No, only one thread can access synchronized method of same object.
110	Same thread accessing other synchronized methods	Yes, same thread can access multiple synchronized methods of same object.
111	Synchronized block	Used to synchronize specific code block instead of entire method.
112	Advantages of synchronized block	Improves performance by locking only required code.
113	Class level lock	Lock applied on class object using static synchronized methods.
114	Synchronize static methods	Yes, using static synchronized.
115	Synchronized block for primitives	No, lock requires object reference not primitive.
116	Thread priorities	Priority decides execution preference of threads.
117	Types of priorities	MIN_PRIORITY(1), NORM_PRIORITY(5), MAX_PRIORITY(10).
118	Change thread priority	Using setPriority() method.
119	Same priority threads	Execution decided by thread scheduler (time slicing).
120	Methods to prevent thread execution	sleep(), wait(), join(), yield().
121	yield() method	Temporarily pauses current thread giving chance to others.
122	Yield thread execution again	Yes, scheduler may schedule it again.
123	join() method	Makes one thread wait until another thread completes.
124	sleep() method	Pauses thread execution for specified time.
125	sleep() and lock	sleep() does NOT release the lock.
126	sleep() affect other threads	No, it only pauses current thread.
127	interrupt() method	Used to interrupt a sleeping or waiting thread.
128	Interthread communication	Communication between threads using wait(), notify(), notifyAll().
129	wait(), notify(), notifyAll()	Used for coordination between threads.
130	Why in Object class	Because every object can be used as monitor for synchronization.
131	IllegalMonitorStateException	Occurs when wait/notify called without owning the object's lock.
132	wait() lock behavior	wait() releases the lock.
133	Methods releasing lock	Only wait() releases lock.
134	Thread groups	Group of threads managed together.
135	ThreadLocal variables	Variables local to each thread.
136	Daemon thread	Background thread supporting main program (e.g., Garbage Collector).
137	Make thread daemon	Using setDaemon(true) before start().
138	Main thread daemon	No, main thread cannot be daemon.

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⭐ Most Important Interview Differences

Topic	Key Point
sleep vs wait	sleep() → Thread class, no lock release
	wait() → Object class, releases lock
Runnable vs Thread	Runnable preferred because supports multiple inheritance
Process vs Thread	Process separate memory, thread shared memory
start() vs run()	start() creates new thread, run() normal method call

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🔥 Memory Trick to Remember Entire Thread Topic

Remember this sequence:

Basic
Creation
Lifecycle
Synchronization
Scheduling
Communication
Advanced

Shortcut:

B C L S S C A

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💡 Interview Tip

If interviewer asks anything about threads, answer using this 3-step template:

Definition
Example
Important point

Example:

Synchronization is a mechanism to control multiple threads
accessing shared resources to avoid race conditions.