Which statement is true for the class java.util.HashSet?
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 statements about the hashcode() method are incorrect?
The value returned by hashcode() is used in some collection classes to help locate objects.
The hashcode() method is required to return a positive int value.
The hashcode() method in the String class is the one inherited from Object.
Two new empty String objects will produce identical hashcodes.
A -
1 and 2
B -
2 and 3
C -
3 and 4
D -
1 and 4
3-
What two statements are true about properly overridden hashCode() and equals() methods?
hashCode() doesn't have to be overridden if equals() is.
equals() doesn't have to be overridden if hashCode() is.
hashCode() can always return the same value, regardless of the object that invoked it.
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
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?
If the equals() method returns true, the hashCode() comparison == must return true.
If the equals() method returns false, the hashCode() comparison != must return true.
If the hashCode() comparison == returns true, the equals() method must return true.
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-
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 property 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)
6-
Which of the following are true statements?
The Iterator interface declares only three methods: hasNext, next and remove.
The ListIterator interface extends both the List and Iterator interfaces.
The ListIterator interface provides forward and backward iteration capabilities.
The ListIterator interface provides the ability to modify the List during iteration.
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
7-
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.
8-
public class Outer
{
public void someOuterMethod()
{
//Line 5
}
public class Inner { }
public static void main(String[] argv)
{
Outer ot = new Outer();
//Line 10
}
}
Which of the following code fragments inserted, will allow to compile?
A -
new ot.Inner(); //At line 10
B -
new Inner(); //At line 10
C -
new Inner(); //At line 5
D -
new Outer.Inner(); //At line 10
9-
What will be the output of the program?
interface Count
{
short counter = 0;
void countUp();
}
public class TestCount implements Count
{
public static void main(String [] args)
{
TestCount t = new TestCount();
t.countUp();
}
public void countUp()
{
for (int x = 6; x>counter; x--, ++counter) /* Line 14 */
{
System.out.print(" " + counter);
}
}
}
A -
1 2 3
B -
0 1 2 3
C -
1 2 3 4
D -
Compilation fails
10-
/* Missing statements ? */
public class NewTreeSet extends java.util.TreeSet
{
public static void main(String [] args)
{
java.util.TreeSet t = new java.util.TreeSet();
t.clear();
}
public void clear()
{
TreeMap m = new TreeMap();
m.clear();
}
}
which two statements, added independently at beginning of the program, allow the code to compile?
