Java Collection Quiz 1 – Java Online Test | Java Question and Answers

How do you get immutable object of a collection ? For example if you were to write an API which return a List or a Set or a Map when a method is called, but you also want that you don´t want the client of your API to add or delete any object in the returned collection ?

Which collection class allows you to grow or shrink its size and provides indexed access to its elements, but whose methods are not synchronized? (Choose all that apply.)

If you were to use a List implementation,but not sure which one to, bacause the requirement is not yet clear. In this case which List implementation will you use ?

Which implementation of Set would you choose if the you want the iterator of set would give you objects in the order it were inserted ?

Tree Set maintains which order?

What is the data structure that a Set uses to store its elements ?

which of the following are false about Collections and Collection ?

If you were to store objects into an implementation of List which happens only once in the entire life cycle of the product, but reading these objects inside the List implementation is quite high, then which one would you use?

Enumeration is an interface helps to iterate collection,but it can´t remove any element the collection it is iterating

What is the output of the following program ?
import java.util.HashSet;

class Animal {
public int i=12;

public Animal(){
i=13;
}
public String toString(){
return “Animal”+i;
}
}
public class Test {
public static void main(String [] args) throws Exception {
HashSet s= new HashSet();
s.add(new Animal());
s.add(new Animal());
for(Animal a : s){
System.out.println(a);
}
}
}

Is Hash Map synchronized?

Set allows at most one null element ?

Is Hashtable synchronized?

Which of the following implementation will you use if you were to insert elements at any position in the collection ?

What is the output of the following program ?
import java.util.HashMap;
import java.util.Map;
public class MapTest {
public static void main(String aga[]){
Map m= new HashMap();
m.put(null, “Test”);
m.put(null,”Fest”);
System.out.println(m);
}
}

What is the default capacity of java.util.Hash Map?

What is the output?

Choose the one below:

What is the output?

Choose the one below:

What is the output?

Can null value be added to a List?