American Express Software Engineer Intern Trainee Interview Questions and Answers

Weak reference is a reference that does not prevent the object from being garbage collected.

• Weak references are used to refer to objects that can be garbage collected if there are no strong references to them.

• They are typically used in scenarios where you want to hold a reference to an object, but don't want to prevent it from being collected.

• Weak references are implemented using weak reference queues, which allow you ...read more

Singleton pattern ensures a class has only one instance, while allowing global access to it.

• Implement a private constructor to prevent direct instantiation.

• Create a static method to provide a single point of access to the instance.

• Use lazy initialization to create the instance only when needed.

• Ensure thread safety in a multithreaded environment using synchronization or double-checked locking.

• Breaking the singleton patt...read more

Annotations used in Spring Framework for defining components and services.

• Annotations like @Component, @Service, and @Controller are used for defining components in Spring Framework.

• @RestController is used for defining RESTful web services.

• @Configuration is used for defining configuration classes.

• @Transactional is used for defining transactional methods.

• All these annotations help in defining and managing dependencies i

HashSet is implemented using a HashMap internally. Same hashcode is generated when two objects have the same value for hashCode() and equals() methods.

• HashSet internally uses a HashMap to store its elements.

• The hashcode of an object is generated using the hashCode() method.

• If two objects have the same value for hashCode() and equals() methods, they will generate the same hashcode.

• For example, if two String objects have...read more

SQL Cursor is a database object used to manipulate data row by row.

• Cursor is used to fetch and process data row by row

• Index is a database object used to speed up data retrieval

• Aggregate functions are used to perform calculations on a set of values

• Examples of aggregate functions are SUM, AVG, COUNT, MAX, MIN

Generate palindrome string with given length and distinct characters.

• Create a char array of length n and fill it with distinct characters.

• Loop through the array and add the characters in reverse order to create a palindrome.

• Repeat the process until the required number of palindromes are generated.

• If k is less than the length of the palindrome, use the first k distinct characters.

Find the highest value that occurs the same number of times within an array.

• Iterate through the array and count the occurrences of each value.

• Store the counts in a dictionary or hash map.

• Find the maximum count and check which value(s) have that count.

• Return the highest value among those with the maximum count.

Count occurrences of a character in a string and output in a specific format.

• Use a hash table to store the count of each character.

• Loop through the string and update the count in the hash table.

• Create the output string using the hash table.

Converts a string from Camel case to Snake case.

• Loop through the string and check for uppercase letters

• Insert an underscore before each uppercase letter

• Convert the string to lowercase

Logic to get Map using Stream API to show balance of each person

• Use Stream API to group accounts by name

• Use map() to get the sum of balances for each group

• Collect the results into a Map