Geodis Overseas Interview Questions and Answers

ConcurrentHashMap allows multiple threads to read/write concurrently, while HashMap is not thread-safe.

• ConcurrentHashMap allows multiple threads to read/write concurrently without blocking each other.

• HashMap is not thread-safe and can lead to data corruption if accessed by multiple threads simultaneously.

• ConcurrentHashMap achieves thread-safety by using internal synchronization mechanisms like locks or CAS operations.

• HashMap does not provide any internal synchronization, so e...read more

Reentrant lock is a synchronization primitive that allows a thread to acquire the same lock multiple times.

• Allows a thread to acquire the same lock multiple times

• Prevents deadlock by allowing a thread to re-enter the lock it already holds

• Useful in situations where a method needs to call another method that also requires the same lock

• Example: Java's ReentrantLock class

Count the number of occurrences of a substring in a given string.

• Use a loop to iterate through the string and check for the substring at each position.

• Use the indexOf method to find the starting index of the substring in the string.

• Increment a counter each time the substring is found.

• Handle edge cases like empty string or null substring.

Multithreading is the ability of a CPU to execute multiple threads concurrently, allowing for parallel processing.

• Multithreading allows for better utilization of CPU resources by running multiple threads simultaneously.

• Threads share the same memory space, allowing for efficient communication and data sharing.

• Examples of multithreading include running multiple tasks in a web server concurrently or processing data in parallel in a video editing software.

HashMap is a data structure that stores key-value pairs and uses hashing to quickly retrieve values based on keys.

• HashMap internally uses an array of linked lists to store key-value pairs.

• When a key-value pair is added, the key is hashed to determine the index in the array where it will be stored.

• If multiple keys hash to the same index, a linked list is used to handle collisions.

• HashMap uses the hashCode() method of keys to calculate the hash value.

• HashMap allows null keys an...read more