Java Software Engineer

The marker interface in Java is an interfaces with no field or methods. In other words, it an empty interface in java is called a marker interface. An example of a marker interface is a Serializable, Clonable and Remote interface. These are used to indicate something to the compiler or JVM.

This question tests the proper usage of collection iterators. One can only use ListIterator to traverse Lists, and cannot traverse a Set using ListIterator.

What’s more, one can only traverse in a forward direction using Iterators. Using ListIterator, one can traverse a List in both the directions (forward and backward).

One cannot obtain indexes while using Iterator. Indexes can be obtained at any point of time while traversing a list using ListIterator. The methods nextIndex() and previousIndex() are used for this purpose.

Java is not 100% Object-oriented because it makes use of eight primitive datatypes such as boolean, byte, char, int, float, double, long, short which are not objects.

If threads are being used and a number of threads have to go through a synchronized section of code, only one of them may be executed at a time. This is used to make sure shared variables are not updated by multiple threads.

ConcurrentHashMap is thread-safe; that is the code can be accessed by single thread at a time while HashMap is not thread-safe. ConcurrentHashMap does not allow NULL keys while HashMap allows it.