10+ Globe Detective Agency Interview Questions and Answers

To make a class immutable in Java, we need to follow certain guidelines.

• Make the class final

• Make all fields private and final

• Do not provide setter methods

• If the field is mutable, return a clone of it instead of the original object

• Ensure that any mutable objects passed to the constructor are not modified outside the class

Autoboxing is the automatic conversion of primitive data types to their corresponding object wrapper classes.

• Autoboxing is useful when working with collections that require objects instead of primitives.

• Example: int i = 5; Integer j = i; //autoboxing

• Unboxing is the opposite of autoboxing, where an object of a wrapper class is converted back to its corresponding primitive type.

• Example: Integer j = 5; int i = j; //unboxing

Program to add numbers in harmonic series (1+1/2+1/3+...+1/n)

• Create a variable to store the sum

• Use a loop to iterate through the series up to n

• Add each term to the sum

• Print the sum

finally is used to execute a block of code after try-catch block, while static block is executed when class is loaded.

• finally block is used to perform cleanup operations like closing database connections, file streams etc.

• static block is used to initialize static variables or perform any other static initialization.

• finally block is always executed whether an exception is thrown or not, while static block is executed only once when class is loaded.

• finally block is always writt...read more

ArrayList and Vector are similar but Vector is synchronized while HashMap and HashTable are both key-value pair data structures but HashTable is synchronized.

• ArrayList and Vector both implement List interface but Vector is thread-safe while ArrayList is not.

• Vector is slower than ArrayList due to synchronization.

• HashMap and HashTable both store key-value pairs but HashTable is thread-safe while HashMap is not.

• HashMap allows null keys and values while HashTable does not.

• HashMap...read more

Typecasting up and down refers to converting a variable of one data type to another data type of higher or lower precision.

• Typecasting up involves converting a variable of lower precision to a variable of higher precision, such as converting an int to a double.

• Typecasting down involves converting a variable of higher precision to a variable of lower precision, such as converting a double to an int.

• Typecasting can result in loss of data or precision.

• Typecasting can be done imp...read more

Java 8 introduced new features like lambda expressions, functional interfaces, streams, and default methods.

• Lambda expressions allow you to write code in a more concise and readable way.

• Functional interfaces provide a single abstract method for functional programming.

• Streams enable processing sequences of elements in a functional style.

• Default methods allow interfaces to have method implementations.

• Example: Lambda expression - (a, b) -> a + b

• Example: Functional interface - Co...read more

Collections are data structures that store and manipulate groups of objects.

• Collections provide a way to manage and manipulate groups of objects

• Java provides several built-in collection classes such as ArrayList, LinkedList, HashSet, etc.

• Collections can be used to perform operations like searching, sorting, filtering, etc.

• Collections can store objects of any type, including primitive types and user-defined classes

The @Autowired annotation in Spring is used to automatically wire dependencies into a bean.

• It eliminates the need for manual wiring of dependencies

• It can be used to inject dependencies into constructors, fields, and methods

• It can be used with other annotations like @Qualifier and @Value

• It can be used with both XML and Java-based configurations

To iterate a map in Java, use a for-each loop or an iterator.

• Use the entrySet() method to get a set of key-value pairs

• For-each loop: for(Map.Entry entry : map.entrySet())

• Iterator: Iterator> iterator = map.entrySet().iterator();

• Use hasNext() and next() methods to iterate through the map

Types of synchronization in Java

• Synchronized methods

• Synchronized statements

• ReentrantLock

• Semaphore

• CountDownLatch

Access modifiers in method overriding

• Access modifiers in the overriding method cannot be more restrictive than the overridden method

• The access modifier can be less restrictive or the same as the overridden method

• Private methods cannot be overridden

• Examples: public method can be overridden by public or protected method, but not by private method

Rest Api is a web service that uses HTTP methods to access and manipulate data.

• Rest stands for Representational State Transfer

• It is an architectural style for building web services

• Uses HTTP methods like GET, POST, PUT, DELETE

• Data is transferred in JSON or XML format

• Examples: Twitter API, Facebook Graph API