Java Core Classes and Threads

This is the correct answer. addFirst() method is used to add the element to the head of the list which is specified in its parameter and this method is present in LinkedList class. So, this is the correct choice.

As I explained that all the methods given in the options are static and are present in Collections class. So, this is the correct choice.

This is the correct choice. poll() method is present in queue interface and it returns and removes the head of the queue and returns null if empty.  

This is the correct choice as removeFirst() method is not present in Vector class; rather it is present in LinkedList class and is used to remove the first element of the list.  

This is the correct answer because there is no method named Merge(c : collection, c1 : collection) in Collections class.  

This is the correct answer. nextIndex() method is present in the ListIterator interface in Java Collections. This method returns the index of the next element in the list to be traversed. So, this is the correct answer.

As all of the functions are defined in the String class, so this is the correct answer.

This is the correct choice. removeAllElements() method is present in Vector class and is used to remove all the elements from the vector.  

This is the correct answer. There is no method named FixedMap() in TreeMap class. So, this method cannot be invoked from Object of TreeMap class. So, this answer is correct.

This is the correct answer. containsKey(object) method is present in the Map interface in Java collections framework. This method returns true if this Map contains a mapping for a specified key. So, this is the correct answer.

This is the correct choice because removeLast() method is not present in the Map interface. It is present in LinkedList class. This method removes the last element from the list.

As explained, all the given methods can be invoked from the object of ConcurrentHashMap class. So, this is the correct choice.

As explained, all the methods are present in the PriorityQueue class. So, this answer is correct.

This is the correct choice because setValue(Value : V) method is not present in the Map interface. This method is present in the Entry interface. This method replaces the value in this entry with a new specified value.

As explained, all the methods can be invoked from the TreeMap object. So, this answer is correct.