Certified Java Programmer Mock Exam

Question 1

Which implementation of the List interface produces the slowest access to an element in the middle of the list by means of an index?

Question 2

import java.util.*;
class GFC100 {
  public static void main (String args[]) {
    Object a1 = new LinkedList(), b1 = new TreeSet();
    Object c1 = new TreeMap();
    System.out.print((a1 instanceof Collection)+",");
    System.out.print((b1 instanceof Collection)+",");
    System.out.print(c1 instanceof Collection);
}}

What is the result of attempting to compile and run the program?

Question 3

Suppose that an instance of class C has legal implementations of the hashCode and equals methods. Within any one execution of the Java application, the hash code contract requires that each invocation of the hashCode method on the same instance of class C must consistently return the same result as long as the fields used for the equals comparison remain unchanged.

Question 4

Which of these classes provides the specified features?

Question 5

import java.util.*;
class GFC101 {
  public static void main (String args[]) {
    Object a1 = new HashMap(), b1 = new ArrayList();
    Object c1 = new HashSet();
    System.out.print((a1 instanceof Collection)+",");
    System.out.print((b1 instanceof Collection)+",");
    System.out.print(c1 instanceof Collection);
}}

What is the result of attempting to compile and run the program?

Question 6

If two instances of a class type are equal according to the equals method, then the same integer value must be returned by the hashCode method of the two objects.

Question 7

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

Question 8

import java.util.*;
class GFC102 {
  public static void main (String args[]) {
    Object a = new HashSet();
    System.out.print((a instanceof Set)+",");
    System.out.print(a instanceof SortedSet);
}}

What is the result of attempting to compile and run the program?

Question 9

If two instances of a class type are not equal according to the equals method, then the same integer value must not be returned by the hashCode method of the two objects.

Question 10

Which implementation of the List interface provides for the fastest insertion of a new element into the middle of the list?

Question 11

import java.util.*;
class GFC103 {
  public static void main (String args[]) {
    Object a1 = new TreeSet();
    System.out.print((a1 instanceof Set)+",");
    System.out.print(a1 instanceof SortedSet);
}}

What is the result of attempting to compile and run the program?

Question 12

class A {
  private int[] val;
  private int hash;
  public int hashCode() {
    int h = hash;
    if (h == 0) {
      int len = val.length;
      for (int i = 0; i < len; i++) {
        h = 31*h + val[i];
      }
      hash = h;
    }
    return h;
  }
  // The equals method has been omitted for clarity.
  A (int[] val) {this.val = (int[])val.clone();}
  public static void main (String[] args) {
    A a = new A(new int[]{1,2,3});
    System.out.print(a.hashCode());
}}

What is the result of attempting to compile and run the program?

Question 13

Which of these classes provides the specified features?

Question 14

import java.util.*;
class GFC104 {
  public static void main (String args[]) {
    LinkedList a1 = new LinkedList();
    ArrayList b1 = new ArrayList();
    Vector c1 = new Vector();
    System.out.print((a1 instanceof List)+",");
    System.out.print((b1 instanceof List)+",");
    System.out.print(c1 instanceof List);
}}

What is the result of attempting to compile and run the program?

Question 15

class A {
  static void m1 (B a, B b, B c, B d, B e, B f, B g, B h) {
    if (a.equals(b)) {System.out.print("A");}
    if (!c.equals(d)) {System.out.print("B");}
    if (e.hashCode() == f.hashCode()) {System.out.print("C");}
    if (g.hashCode() != h.hashCode()) {System.out.print("D");}
}}

Suppose that method m1 is invoked with eight instances of the same class and the output is ABCD. If the B.equals and B.hashCode methods are implemented according to the hash code contract, then which of the following statements must always be true?

Question 16

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

Question 17

import java.util.*;
class GFC105 {
  public static void main (String args[]) {
    Object a = new HashSet(), b = new HashMap();
    Object c = new Hashtable();
    System.out.print((a instanceof Collection)+",");
    System.out.print((b instanceof Collection)+",");
    System.out.print(c instanceof Collection);
}}

What is the result of attempting to compile and run the program?

Question 18

class B {
  private int i1;
  public int hashCode() {return 1;}
}
class C {
  private int i1;
  public int hashCode() {return -1;}
}
class D {
  private int i1;
  public int hashCode() {return i1;}
}

Suppose that the equals method of classes B, C and D all make use of the value of the int variable, i1. Which class has a hashCode method that is not consistent with the hash code contract?