Objects and Collections

1

Which statement is true for the class java.util.ArrayList?

A. The elements in the collection are ordered.
B. The collection is guaranteed to be immutable.
C. The elements in the collection are guaranteed to be unique.
D. The elements in the collection are accessed using a unique key.

2

Which of the following are true statements?

    1. The Iterator interface declares only three methods: hasNext, next and remove.

    2. The ListIterator interface extends both the List and Iterator interfaces.

    3. The ListIterator interface provides forward and backward iteration capabilities.

    4. The ListIterator interface provides the ability to modify the List during iteration.

    5. The ListIterator interface provides the ability to determine its position in the List.


A. 2, 3, 4 and 5
B. 1, 3, 4 and 5
C. 3, 4 and 5
D. 1, 2 and 3

3
x = 0;
if (x1.hashCode() != x2.hashCode() )  x = x + 1;
if (x3.equals(x4) )  x = x + 10;
if (!x5.equals(x6) ) x = x + 100;
if (x7.hashCode() == x8.hashCode() )  x = x + 1000;
System.out.println("x = " + x);

and assuming that the equals() and hashCode() methods are properly implemented,if the

output is "x = 1111", which of the following statements will always be true?

A. x2.equals(x1)
B. x3.hashCode() == x4.hashCode()
C. x5.hashCode() != x6.hashCode()
D. x8.equals(x7)

4

Which two statements are true about comparing two instances of the same class, given that the equals() and hashCode() methods have been properly overridden?

    1. If the equals() method returns true, the hashCode() comparison == must return true.

    2. If the equals() method returns false, the hashCode() comparison != must return true.

    3. If the hashCode() comparison == returns true, the equals() method must return true.

    4. If the hashCode() comparison == returns true, the equals() method might return true.

A. 1 and 4
B. 2 and 3
C. 3 and 4
D. 1 and 3

5

What two statements are true about properly overridden hashCode() and equals() methods?

    1. hashCode() doesn't have to be overridden if equals() is.

    2. equals() doesn't have to be overridden if hashCode() is.

    3. hashCode() can always return the same value, regardless of the object that invoked it.

    4. equals() can be true even if it's comparing different objects.

A. 1 and 2
B. 2 and 3
C. 3 and 4
D. 1 and 3