Frequently asked Advanced Java Thread and Java Exceptions Interview Questions and Answers for 2-6 year experienced Java developers, Senior software engineers, Tech Lead and freshers.
1) What is meant by Thread ?
A thread is a path of execution of a Program. A Thread is a sequence of instructions that executed in a predefined unique flow of control. Advantages of thread are
- Reduces development time
- Reduces maintenance costs
- Improves the performance of complex applications
- Useful for improving the responsiveness of the user interfaces
- Used in server applications for improving high throughput and resource utilization
2) Explain Thread Life Cycle ?
Thread Life cycle have four states as below
- New - While thread is initialized, it will enter to init state. After initialization, we should call start() method. If start method is not called, java throws IllegalThreadStateException.
- Runnable - Once a start method is called then it will enter to runnable state. Resources and schedules associated with the thread is allocated by start method. Then it will call run() method.
- Not Runnable
- sleep() - Wait for specified time
- wait() - Wait until notify.
- suspend() - Blocked by another thread
- Dead - if the run method gets completed or thread object is assigned a null value, its enter into dead state.
3) What are the differences between Thread and process ?
| Process | Thread |
|---|---|
| It has own address. | Share the address space of the process. |
| It has their own copy of the data segment of the parent process. | It have direct access to the data segment of its process. |
| It must use interprocess communication to communicate with sibling processes. | Threads can directly communicate with other threads of its process |
| Changes to the parent process do not affect child processes. | Changes to the main thread like cancellation or change in priority of thread may affect the behaviour of the other threads of the process |
4) Is it possible to restart the dead Thread in Java ?
No. A thread can't be restarted once the execution is completed.
5) Can you explain about Synchronized keyword in Java ?
When 2 or more threads try to access a shared object, Java throws thread interference and memory consistency errors. To overcome this scenario, we need to synchronize java objects using Synchronized keyword. We can use synchronize keyword in
- Used in method - public void synchronized method { // access code}
- Used in block - synchronized(obj) { // access code}
6) How object are communicate with each other in synchronized context ?
In all the classes, final methods like wait, notify and notifyAll has been implemented. All three methods can be called only from within a synchronized context. Using these methods object are communicated with each other in synchronized context.
7) What is the difference between sleep() and wait() ?
| Sleep() | Wait() |
|---|---|
| Thread stops working for the specified duration. | Thread stops working until the object in waiting is notified. |
| Thread method. | Object method |
| It doesn’t release the lock while waiting. | It releases lock on object while waiting. |
| Put thread on sleep | It is normally done on condition. |
8) How to stop a running thread in Java ?
Thread will stop once come out of run method. So one of the way to stop a thread as follows
public class MyThread extends Thread {
@Override
public void run() {
while (!this.isInterrupted()) {
}
}
}
// To stop a thread, call method interrupt():
myThread.interrupt();
9) What is the difference between notify() and notifyAll() ?
| notify | notifyAll |
|---|---|
| Used to wake up a single thread | All threads in wait state wakes up. |
