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1. 

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.  

class Test1 
{
    public int value;
    public int hashCode() { return 42; }
}
class Test2 
{
    public int value;
    public int hashcode() { return (int)(value^5); }
}
which statement is true?
A. class Test1 will not compile.
B. The Test1 hashCode() method is more efficient than the Test2 hashCode() method.
C. The Test1 hashCode() method is less efficient than the Test2 hashCode() method.
D. class Test2 will not compile.
3. 

Which of the following statements about the hashcode() method are incorrect?

  1. The value returned by hashcode() is used in some collection classes to help locate objects.
  2. The hashcode() method is required to return a positive int value.
  3. The hashcode() method in the String class is the one inherited from Object.
  4. 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
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.  

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)