Set - 4

Question 6 :

How to check two arrays to see if contents have the same types and contain the same elements?

Answer :

One of options is to use the equals() method of Arrays class.

Arrays.equals(a, b);

If the array types are different, a compile-time error will happen.


Question 7 :

Can you call one constructor from another if a class has multiple constructors?

Answer :

Yes. Use this() syntax.


Question 8 :

What are the different types of inner classes?

Answer :

There are four different types of inner classes in Java. They are: a)Static member classes , a static member class has access to all static methods of the parent, or top-level, class b) Member classes, the member class is instance specific and has access to any and all methods and members, even the parent's this reference c) Local classes, are declared within a block of code and are visible only within that block, just as any other method variable. d) Anonymous classes, is a local class that has no name


Question 9 :

In which case would you choose a static inner class?

Answer :

Interesting one, static inner classes can access the outer class's protected and private fields. This is both a positive and a negative point for us since we can, in essence, violate the encapsulation of the outer class by mucking up the outer class's protected and private fields. The only proper use of that capability is to write white-box tests of the class -- since we can induce cases that might be very hard to induce via normal black-box tests (which don't have access to the internal state of the object). Second advantage,if I can say, is that, we can this static concept to impose restriction on the inner class. Again as discussed in earlier point, an Inner class has access to all the public, private and protected members of the parent class. Suppose you want to restrict the access even to inner class, how would you go ahead? Making the inner class static enforces it to access only the public static members of the outer class( Since, protected and private members are not supposed to be static and that static members can access only other static members). If it has to access any non-static member, it has to create an instance of the outer class which leads to accessing only public members.


Question 10 :

What is weak reference in Java

Answer :

A weak reference is one that does not prevent the referenced object from being garbage collected. You might use them to manage a HashMap to look up a cache of objects. A weak reference is a reference that does not keep the object it refers to alive. A weak reference is not counted as a reference in garbage collection. If the object is not referred to elsewhere as well, it will be garbage collected.