Java Collections Dr LJK

-Contains no duplicate elements.

-Can contain at most one Null value.

-Elements are not key-value pairs.

-Accessing an element can be almost as fast as performing a similar operation on an array.

Which of these classes provides the specified features?

• LinkedList

• TreeMap

• HashSet

• LinkedHashMap

• HashMap

• 4

• 5

• 6

• 12

-Entries are not organized as key/value pairs.

-Duplicate entries are rejected.

Which interface of the java.util package offers the specified behavior?

• List

• Map

• Set

• None of the above

• [Computer, Network, Networks, Programming, Security]

• [Computer, Programming, Network, Networks, Programming, Security]

• [Computer, Programming, Computer, Networks, Network, Security]

• [Computer, Networks, Network, Programming, Security]

Which of the following is/are correct statements?

• HashSet class implements the Set interface

• HashSet does not allow duplicate elements that means you can not store duplicate values in HashSet.

• HashSet permits to have a single null value.

• HashMap does not allow duplicate keys however it allows to have duplicate values.

• HashMap and HashSet are threadsafe

List listNames = new ArrayList();

listNames.add("Tom");

listNames.add("Mary");

listNames.add("Peter");

String name2 = (String) listNames.get(1);

System.out.println(name2);

What is the output of the above code

• Tom

• Mary

• Peter

• raises Exception

What is the list nums if it is initially [5, 3, 1] and the following code is executed?

nums.add(6);

nums.add(0, 4);

nums.remove(1);

• [4, 3, 1, 6]

• [5, 3, 1, 6]

• [4, 3, 6]

• [4, 5, 3, 6]

What will print when the following code executes?

ArrayList<Integer> list = new ArrayList<Integer>();

list.add(7);

list.add(8);

list.add(9);

System.out.println(list.remove(0));

• 7

• 8

• 9

• 0

What is printed as a result of executing the following code segment?

ArrayList<Double> vals = new ArrayList<Double>();

vals.add(3.5);

vals.add(4.5);

vals.add(5.5);

vals.add( vals.set(0, 2.5) );

System.out.println(vals);

• [2.5, 4.5, 5.5, 3.5]

• [2.5, 3.5, 4.5, 5.5]

• [3.5, 4.5, 5.5, 2.5]

• [2.5, 4.5, 5.5]

Which statement is the correct declaration and initialization of an ArrayList of String values?

• ArrayList<String> name;

  name = new ArrayList<String>();

• ArrayList name;

  name = new ArrayList<String>();

• ArrayList<String> name;

  name = ArrayList<String>();

• String<ArrayList> name;

  name = new String<ArrayList>();