Persistent Systems Trainee Interview Questions and Answers

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; //unboxi

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 resul...read more

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