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Ans. Java provides its own implementations of the thread pool pattern, through objects called executors. These can be used through executor interfaces or directly through thread pool implementations which does allow for finer-grained control. The java.util.concurrent package contains the following interfaces:
Executor : a simple interface for executing tasks.ExecutorService a more complex interface which contains additional methods for managing the tasks and the executor itself.
ScheduledExecutorService: extends ExecutorService with methods for scheduling the execution of a task.Alongside these interfaces, the package also provides the Executors helper class for obtaining executor instances, as well as implementations for these interfaces.
Generally, a Java thread pool is composed of:
The pool of worker threads, responsible for managing the threads.
A thread factory that is responsible for creating new threads.
A queue of tasks waiting to be executed.
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Ans. Singleton class will have only one instance through out your application. Once the instance has been created, you can use it to change the state of that object, whereas for immutable class you cannot change the value that means you cannot change the state of it once assigned.
If you want to change the state/ different values, you can very well create two instance for that immutable class which JVM will allow.
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Q33. suppose i have interface and i have declare lots of abstract method in interface But in sub class only two methods are use .than how to use oly two methods.
Ans. The load-on-startup element of web-app loads the servlet at the time of deployment or server start if value is positive. It is also known as pre initialization of servlet.You can pass positive and negative value for the servlet.
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Q37. While working on a web application, you are informed that there is no new data in Database for last few hours ? How would you go about debugging this problem ?
Ans. Will look into access logs to see if web application is getting any traffic. If not , then will inform the server support team.
Will look into intermediary infrastructure , queues , streams etc to see if there is any choke or throttle there.
If there is any throttle at any point, would make request for either debugging the cause or increasing the infrastructure. For ex - increasing shards in Kinesis.
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Q43. Suppose we make an api call using multithreading, How would you design to make sure that we have received response for all threads before exiting the main thread ?
Ans. We can use HashMap for tracking response status for all threads. We can wait every n second by using Thread.sleep and exit the main thread only once we have received response for all threads.
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Q50. Given a String with letters , numbers and special characters , extract Tokens from it. The rules for Token extraction are ac follows
1. Should for token of all characters till a number or special character is found
2. Should form token of all numbers till a character or special character is found
3. Special character in itself is a token
4. Ignore white spaces
For example - Bob Said "He is here"
should result in
Bob A
Said A
" S
He A
is A
here A
" S
where a is specifying alphabet and S as special character
Ans. Subject has state, it keeps a list of observers. On the other hand, an Observable is really just a function that sets up observation. While Subjects are Observables, Subjects also implement an Observer interface.
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