Wissen Technology Java Developer Interview Questions, Process, and Tips for Experienced

Q1. What is the contract between hashCode and equals method?
Ans. 
The contract between hashCode and equals method is that if two objects are equal according to the equals method, then their hash codes must also be equal.
• hashCode and equals method must be consistent - if two objects are equal according to equals method, their hash codes must be equal

• If two objects have the same hash code, they may or may not be equal according to equals method

• Overriding equals method in a class requir...read more
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Q2. Features introduced in Java 8
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Java 8 introduced several new features including lambda expressions, functional interfaces, streams, and default methods in interfaces.
• Lambda expressions allow you to pass functions as arguments.

• Functional interfaces have a single abstract method and can be used with lambda expressions.

• Streams provide a way to work with sequences of elements.

• Default methods allow interfaces to have method implementations.
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Q3. What are the ways to start a thread
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Ways to start a thread in Java
• Extending the Thread class and overriding the run() method

• Implementing the Runnable interface and passing it to a Thread object

• Using a thread pool from the Executors class
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Q4. What will happen if you start a thread which is already running
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The thread will continue running as it is already active
• The thread will not be started again if it is already running

• Attempting to start a thread that is already running will not have any effect

• The thread will continue its execution without any interruption
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Q5. Explain about the join and sleep method
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Join method is used to wait for a thread to finish its execution, while sleep method is used to pause the execution of a thread for a specified amount of time.
• Join method is used to wait for a thread to finish its execution before moving on to the next task.

• Sleep method is used to pause the execution of a thread for a specified amount of time, allowing other threads to run.

• Example: thread1.join() will wait for thread1 ...read more
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Q1. Merge 2 sorted array
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Q2. Flatten the 2D dimensional array
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Q1. Java questions on multithreading, data structures, and algorithms
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Q1. Puzzle questions, complete the code questions
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Test has a 8 question in that 5 are mcqs and 2 are coding and 1 is SQL query.

Q1. F2F interview was there. Basic of Multithreading in java. Split array into chunks of given size. Class level and Object level synchronization. Given a nested array and make it into flatten array. {{1}, 2...read more
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Q1. After this we have a 3rd F2F round- What is Multithreading in java?
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Q2. Convert String camel case to snake case.
Ans. 
Converts a camel case string to snake case.
• Split the string by uppercase letters

• Convert each word to lowercase

• Join the words with underscores
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Q3. Write a Java program using multithreading to print below output: n=10 Thread-1 : 1 Thread-2 : 2 Thread-3 : 3 Thread-1 : 4 Thread-2 : 6 . . Thread-1 : 10
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A Java program using multithreading to print numbers from 1 to 10 in a specific pattern.
• Create three threads and assign them to print numbers in a specific pattern

• Use synchronization to ensure the correct order of printing

• Use a loop to iterate from 1 to 10 and assign the numbers to the threads

• Print the thread name and the assigned number in the desired format
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Q4. Suggestion on best way for Java collection to store csv data. and if needed any operation on how to do? there are millions of data need to store in java collection. and some validations on this.
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Q5. How to detect a loop into LinkedList?
Ans. 
To detect a loop in a LinkedList, we can use the Floyd's cycle-finding algorithm.
• Initialize two pointers, slow and fast, both pointing to the head of the LinkedList.

• Move slow pointer by one step and fast pointer by two steps at a time.

• If there is a loop, the slow and fast pointers will eventually meet.

• If either of the pointers reaches the end of the LinkedList, there is no loop.
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Q6. Difference between Callable and Runnable Class?
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Callable and Runnable are interfaces in Java used for concurrent programming. Callable returns a result and can throw an exception, while Runnable does not return a result or throw an exception.
• Callable is a generic interface with a method called 'call()', while Runnable is a functional interface with a method called 'run()'.

• Callable can return a result using the 'Future' interface, while Runnable cannot.

• Callable can t...read more
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Q7. How to create Thread in Java and What are the ways?
Ans. 
Threads in Java allow concurrent execution of multiple tasks. They can be created in multiple ways.
• Using the Thread class

• Implementing the Runnable interface

• Using the Executor framework

• Using the Callable interface with ExecutorService
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Q8. Write a SQL Query for having student table Name Subjects Marks Data like- abc Eng 19 abc Phy 17 abc Chem 20 xyz Eng 16 xyz Phy 18 xyz Chem 12 ..... output should be like a list display at the marks board ...read more
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