Updated June 26, 2023
Introduction to Java Multi-threading Interview Questions
Java is on boom these days due to its independent platform. So you have finally found your dream job in Java Multithreading but are wondering how to crack the interview and what the probable 2023 Java Multithreading Interview Questions could be. Every interview is different, and the job scope is different too. Let us go through a few critical Java Multithreading Interview Questions that may be asked in the Java Multithreading interviews you would pursue.
Part 1 – Java Multithreading Interview Questions (Basic)
This first part covers basic Java Multi-threading Interview Questions.
1. What is Thread in JAVA, and how do you implement it?
Answer:
A thread helps facilitates multi-tasking and multi-processing within a program. It utilizes the CPU effectively and helps improve the performance of the application. Java enables the user to use multiple threads at a time. It can run in parallel with other programs without any interruptions. This helps in reducing the time for the process. For example, if a program takes 60 seconds to execute, we can use six threads to give us the result in 10 seconds.
Java provides two ways to implement threads in a program. Interface java.Lang.Runnable has an instance of Java.lang.A line that requires a task to execute through an instance. The Thread class already implements Runnable, so a user can directly override the run() method by extending the Thread class or implementing the Runnable interface.
2. When to use Runnable and when to use Thread in Java?
Answer:
Java does not support multiple inheritances of a class, but it allows us to implement various interfaces simultaneously. Therefore, it will be better to implement Runnable than to extend the Thread class.
3. How do you differentiate between a thread and a process?
Answer:
A thread is a subset of a process. One process can have multiple lines running for it. Cables can run any part of a process. Creating a strategy is hectic, while threads can be made quickly. Interprocess communication is difficult, while threads can communicate easily using the Java methods of wait() and notify(). Functions are independent; hence any change made to a process does not affect child processes. On the contrary, if changes are made in a thread, there are possibilities that other lines may be affected.
4. Why is it said that Thread’s behavior is unpredictable?
Answer:
The reason for this is the thread scheduler which handles the execution of threads. The scheduler may perform different performances on different Windows, UNIX, LINUX platforms, etc. While executing, the same Thread may give different outputs on various platforms and sometimes even on the same platform. To solve this, a user can create the same Runnable object, create run() loops in both threads and start both lines together.
5. What is a volatile variable in Java, and what is its significance?
Answer:
Java facilitates users to share variables present in different threads. A volatile variable acts as a unique modifier that can be used only for instance variables. It provides that a write will happen before any consequent read. The Java memory model ensures the consistency of this variable.
Part 2 – Java Multithreading Interview Questions (advanced)
This first part covers advanced Interview Questions and Answers
1. What is the use of the synchronized keyword? What is the difference between synchronized and volatile keywords?
Answer:
The synchronized keyword is used when the purpose Is to run only one Thread at a time in an appropriate section of code. It can be used to show four types of different blocks as below:
- Instance methods
- Static methods
- Code blocks inside instance methods
- Code blocks inside static methods
It can be declared as follows:
Public synchronized void example () {}
A volatile variable will never land up in a deadlock as it does not require obtaining any lock. While in synchronized variables, it may end up in a draw if they are not done correctly.
2. Why methods like wait(), notify(), and notify all() are present in the object class and not in the Thread class?
Answer:
Object class has monitors that allow the Thread to lock an object, while Thread does not have any monitors. The object class’s monitor checks for the thing to see if it is available. Thread class having these methods would not help as multiple threads exist on an object, not vice versa.
3. Explain the difference between sleep() and wait() methods.
Answer:
- When the wait() method is called, the monitor moves the Thread from running to waiting for the state. Once a thread is in wait(), then it can move to runnable only when it has notified () or told all () for that object. The scheduler changes the state after this. While in the sleep() method, the state is changed to wait and will return to runnable only after sleep time.
- The wait () method is a part of Java.lang.Object class, while sleep() is a part of Java.lang.Thread class.
4. How to force start a thread in Java?
Answer:
In Java, multithreading, one cannot force start a thread. Only thread schedulers can control lines and are not exposed to any API for control.
5. Does Thread leave object lock when wait() and sleep() methods are called?
Answer:
A thread in the sleep() method does not leave the lock and moves to the waiting state. The Thread waits for sleep time to get over.
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