SCJP Mock exam for Generics

SCJP Mock exam for Generics

59 Votes

A collection of structured questions for Generics, under the scope of Sun Certified Java Programmer for Java SE 6.

If you are busy, just go through questions 1-40.

questions	topic
1-24	assignment and hierarchy
25-40	add and get elements from a generic collection
41-50	overloading and overriding
51-60	various details
61-72	declaration of generic classes

1. Will this code compile successfully? (1 correct answer)

   List<Number> list1 = null;
   List<Integer> list2 = null;
   list1 = list2;
   

   1. Yes.
   2. No.
2. Will this code compile successfully? (1 correct answer)

   List<Number> list1 = null;
   List<Integer> list2 = null;
   list2 = list1;
   

   1. Yes.
   2. No.
3. Will this code compile successfully? (1 correct answer)

   List<? extends Number> list1 = null;
   List<Integer> list2 = null;
   list1 = list2;
   

   1. Yes.
   2. No.
4. Will this code compile successfully? (1 correct answer)

   List<? extends Number> list1 = null;
   List<Integer> list2 = null;
   list2 = list1;
   

   1. Yes.
   2. No.
5. Will this code compile successfully? (1 correct answer)

   List<Number> list1 = null;
   List<? super Integer> list2 = null;
   list1 = list2;
   

   1. Yes.
   2. No.
6. Will this code compile successfully? (1 correct answer)

   List<Number> list1 = null;
   List<? super Integer> list2 = null;
   list2 = list1;
   

   1. Yes.
   2. No.
7. Will this code compile successfully? (1 correct answer)

   SortedSet<? super Number> set1 = null;
   SortedSet<Integer> set2 = null;
   set1 = set2;
   

   1. Yes.
   2. No.
8. Will this code compile successfully? (1 correct answer)

   SortedSet<? super Number> set1 = null;
   SortedSet<Integer> set2 = null;
   set2 = set1;
   

   1. Yes.
   2. No.
9. Will this code compile successfully? (1 correct answer)

   SortedSet<Number> set1 = null;
   SortedSet<? extends Integer> set2 = null;
   set1 = set2;
   

   1. Yes.
   2. No.
10. Will this code compile successfully? (1 correct answer)

    SortedSet<Number> set1 = null;
    SortedSet<? extends Integer> set2 = null;
    set2 = set1;
    

    1. Yes.
    2. No.
11. Will this code compile successfully? (1 correct answer)

    Queue<? extends Number> q1 = null;
    Queue<? super Integer> q2 = null;
    q1 = q2;
    

    1. Yes.
    2. No.
12. Will this code compile successfully? (1 correct answer)

    Queue<? extends Number> q1 = null;
    Queue<? super Integer> q2 = null;
    q2 = q1;
    

    1. Yes.
    2. No.
13. Will this code compile successfully? (1 correct answer)

    Queue<? super Number> q1 = null;
    Queue<? extends Integer> q2 = null;
    q1 = q2;
    

    1. Yes.
    2. No.
14. Will this code compile successfully? (1 correct answer)

    Queue<? super Number> q1 = null;
    Queue<? extends Integer> q2 = null;
    q2 = q1;
    

    1. Yes.
    2. No.
15. Will this code compile successfully? (1 correct answer)

    Queue<?> q1 = null;
    Queue<Integer> q2 = null;
    q1 = q2;
    

    1. Yes.
    2. No.
16. Will this code compile successfully? (1 correct answer)

    LinkedList<?> list1 = null;
    LinkedList<Integer> list2 = null;
    list2 = list1;
    

    1. Yes.
    2. No.
17. Will this code compile successfully? (1 correct answer)

    LinkedList<?> list1 = null;
    LinkedList<? extends Integer> list2 = null;
    list1 = list2;
    

    1. Yes.
    2. No.
18. Will this code compile successfully? (1 correct answer)

    LinkedList<?> list1 = null;
    LinkedList<? extends Integer> list2 = null;
    list2 = list1;
    

    1. Yes.
    2. No.
19. Will this code compile successfully? (1 correct answer)

    LinkedList<?> list1 = null;
    LinkedList<? super Integer> list2 = null;
    list1 = list2;
    

    1. Yes.
    2. No.
20. Will this code compile successfully? (1 correct answer)

    LinkedList<?> list1 = null;
    LinkedList<? super Integer> list2 = null;
    list2 = list1;
    

    1. Yes.
    2. No.
21. Will this code compile successfully? (1 correct answer)

    PriorityQueue queue1 = null;
    PriorityQueue<Integer> queue2 = null;
    queue1 = queue2;
    

    1. Yes, without warnings.
    2. Yes, with a warning.
    3. No.
22. Will this code compile successfully? (1 correct answer)

    PriorityQueue queue1 = null;
    PriorityQueue<Integer> queue2 = null;
    queue2 = queue1;
    

    1. Yes, without warnings.
    2. Yes, with a warning.
    3. No.
23. Will this code compile successfully? (1 correct answer)

    PriorityQueue<?> queue1 = null;
    PriorityQueue queue2 = null;
    queue1 = queue2;
    

    1. Yes, without warnings.
    2. Yes, with a warning.
    3. No.
24. Will this code compile successfully? (1 correct answer)

    PriorityQueue<?> queue1 = null;
    PriorityQueue queue2 = null;
    queue1 = queue2;
    

    1. Yes, without warnings.
    2. Yes, with a warning.
    3. No.
25. Will this code compile successfully? (1 correct answer)

    Set<Integer> set = new TreeSet<Integer>();
    set.add(10);
    

    1. Yes.
    2. No.
26. Will this code compile successfully? (1 correct answer)

    Set<Integer> set = new TreeSet<Integer>();  
    set.add((int)1.0f);
    

    1. Yes.
    2. No.
27. Will this code compile successfully? (1 correct answer)

    Set<Integer> set = new TreeSet<Integer>();
    set.add(10L);
    

    1. Yes.
    2. No.
28. Will this code compile successfully? (1 correct answer)

    Set<Integer> set = new TreeSet<Integer>();
    int number = (short)10;
    set.add(number);
    

    1. Yes.
    2. No.
29. Will this code compile successfully? (1 correct answer)

    Set<Number> set = new TreeSet<Integer>();
    set.add(10L);
    

    1. Yes.
    2. No.
30. Will this code compile successfully? (1 correct answer)

    NavigableSet<?> set = new TreeSet<Object>();
    set.add(new Object());
    

    1. Yes.
    2. No.
31. Will this code compile successfully? (1 correct answer)

    NavigableSet<? super Object> set = new TreeSet<Object>();
    set.add(new Object());
    

    1. Yes.
    2. No.
32. Will this code compile successfully? (1 correct answer)

    NavigableSet<? extends Object> set = new TreeSet<Object>();
    set.add(new Object());
    

    1. Yes.
    2. No.
33. Will this code compile successfully? (1 correct answer)

    NavigableSet<? extends String> set = new TreeSet<String>();
    set.add("string

    1. Yes.
    2. No.
34. Will this code compile successfully? (1 correct answer)

    NavigableSet<? super String> set = new TreeSet<String>();
    set.add("string

    1. Yes.
    2. No.
35. Will this code compile successfully? (1 correct answer)

    NavigableSet<? super String> set = new TreeSet<String>();
    set.add(new Object());
    

    1. Yes.
    2. No.
36. Will this code compile successfully? (1 correct answer)

    List<? extends Integer> list = new ArrayList<Integer>();
    for (Integer element : list) {
     System.out.println(element);
    }
    

    1. Yes.
    2. No.
37. Will this code compile successfully? (1 correct answer)

    List<? extends Integer> list = new ArrayList<Integer>();
    Integer first = list.get(0);
    

    1. Yes.
    2. No.
38. Will this code compile successfully? (1 correct answer)

    List<? super Integer> list = new ArrayList<Integer>();
    for (Integer element : list) {
     System.out.println(element);
    }
    

    1. Yes.
    2. No.
39. Will this code compile successfully? (1 correct answer)

    List<? super Integer> list = new ArrayList<Integer>();
    Integer first = list.get(0);
    

    1. Yes.
    2. No.
40. Will this code compile successfully? (1 correct answer)

    List<? super Integer> list = new ArrayList<Integer>();
    Object first = list.get(0);
    

    1. Yes.
    2. No.
41. Will this code compile successfully? (1 correct answer)

    import java.util.*;
    
    class Test {
        void say(Set<Double> set) {
        }
        void say(SortedSet<Double> set) {
        }
    }
    

    1. Yes.
    2. No.
42. Will this code compile successfully? (1 correct answer)

    import java.util.*;
    
    class Test {
        void say(Set<Double> set) {
        }
        void say(Set<Boolean> set) {
        }
    }
    

    1. Yes.
    2. No.
43. Will this code compile successfully? (1 correct answer)

    import java.util.*;
    
    class Test {
        void say(Set<Double> set) {
        }
        void say(Set<Double>... set) {
        }
    }
    

    1. Yes.
    2. No.
44. Consider these classes.

    import java.util.*;
    
    class Parent {
     void say(List<String> list) {
      System.out.println("parent}
    }
    class Child extends Parent {
     void say(List list) {
      System.out.println("child}
    }
    

    What happens when this code is compiled and executed? (1 correct answer)
    

    public static void main(String[] java) {
     Child c = new Child();
     c.say(new LinkedList<String>());
    }
    

    1. It prints “child”.
    2. It prints “parent”.
    3. Compilation fails.
45. Consider these classes.

    import java.util.*;
    
    class Parent {
     void say(List<String> list) {
      System.out.println("parent}
    }
    class Child extends Parent {
     void say(List list) {
      System.out.println("child}
    }
    

    What happens when this code is compiled and executed? (1 correct answer)
    

    public static void main(String[] java) {
     Child c = new Child();
     c.say(new LinkedList<List<Boolean>>());
    }
    

    1. It prints “child”.
    2. It prints “parent”.
    3. Compilation fails.
46. Consider these classes.

    import java.util.*;
    
    class Parent {
     void say(List<String> list) {
      System.out.println("parent}
    }
    class Child extends Parent {
     void say(List list) {
      System.out.println("child}
    }
    

    What happens when this code is compiled and executed? (1 correct answer)
    

    public static void main(String[] java) {
     Parent c = new Child();
     c.say(new LinkedList<String>());
    }
    

    1. It prints “child”.
    2. It prints “parent”.
    3. Compilation fails.
47. Consider these classes.

    import java.util.*;
    
    class Parent {
     void say(List<String> list) {
      System.out.println("parent}
    }
    class Child extends Parent {
     void say(List list) {
      System.out.println("child}
    }
    

    What happens when this code is compiled and executed? (1 correct answer)
    

    public static void main(String[] java) {
     Parent c = new Child();
     c.say(new LinkedList<Long>());
    }
    

    1. It prints “child”.
    2. It prints “parent”.
    3. Compilation fails.
48. Will this code compile successfully? (1 correct answer)

    import java.util.*;
    
    class Parent {
     void say(List<String> list) {
      System.out.println("parent}
    }
    class Child extends Parent {
     void say(List<Integer> list) {
      System.out.println("child}
    }
    

    1. Yes.
    2. No.
49. Will this code compile successfully? (1 correct answer)

    import java.util.*;
    
    class Parent {
     void say(List<? extends Number> list) {
      System.out.println("parent}
    }
    class Child extends Parent {
     void say(List<Integer> list) {
      System.out.println("child}
    }
    

    1. Yes.
    2. No.
50. Will this code compile successfully? (1 correct answer)

    import java.util.*;
    
    class Parent {
     void say(List list) {
      System.out.println("parent}
    }
    class Child extends Parent {
     void say(List<Integer> list) {
      System.out.println("child}
    }
    

    1. Yes.
    2. No.
51. Will this code compile successfully? (1 correct answer)

    Object set = new TreeSet<Integer>();
    boolean flag = set instanceof NavigableSet<Integer>;
    

    1. Yes.
    2. No.
52. What is the output of the following code? (1 correct answer)

    List<? extends String> list1 = new ArrayList<String>();
    List<? super String> list2 = new ArrayList<String>();
    List<Integer> list3 = new ArrayList<Integer>();
    List list4 = new ArrayList();
    
    if (list1 instanceof List && 
        list2 instanceof List &&
        list3 instanceof List &&
        list4 instanceof List) {
        System.out.println("yes
    

    1. It prints “yes”.
    2. It prints nothing.
53. Will this code compile successfully? (1 correct answer)

    Class c = ArrayList<Integer>.class;
    

    1. Yes.
    2. No.
54. Will this code compile successfully? (1 correct answer)

    Class c = new ArrayList<Integer>().getClass();
    

    1. Yes.
    2. No.
55. Will this code compile successfully? (1 correct answer)

    new ArrayList<?>();
    

    1. Yes.
    2. No.
56. Will this code compile successfully? (1 correct answer)

    new TreeMap<String, ? super Integer>();
    

    1. Yes.
    2. No.
57. Will this code compile successfully? (1 correct answer)

    new ArrayList<Set<?>>();
    

    1. Yes.
    2. No.
58. Will this code compile successfully? (1 correct answer)

    class Test extends ArrayList<? extends Number> {
    }
    

    1. Yes.
    2. No.
59. Will this code compile successfully? (1 correct answer)

    class Test implements Comparable<?> {
        public int compareTo(Comparable<?> object) {
            return 0;
        }
    }
    

    1. Yes.
    2. No.
60. Will this code compile successfully? (1 correct answer)

    class Test implements Comparable<Comparable<?>> {
        public int compareTo(Comparable<?> object) {
            return 0;
        }
    }
    

    1. Yes.
    2. No.
61. Will this code compile successfully? (1 correct answer)

    class Test {
    <T> T getFirst(List<T> list) {
        return list.get(0);
    }
    }
    

    1. Yes.
    2. No.
62. Will this code compile successfully? (1 correct answer)

    class Test {
    static <T> T getFirst(List<T> list) {
        return list.get(0);
    }
    }
    

    1. Yes.
    2. No.
63. Will this code compile successfully? (1 correct answer)

    class Test <T> {
    T getFirst(List<T> list) {
        return list.get(0);
    }
    }
    

    1. Yes.
    2. No.
64. Will this code compile successfully? (1 correct answer)

    class Test <T> {
    static T getFirst(List<T> list) {
        return list.get(0);
    }
    }
    

    1. Yes.
    2. No.
65. Will this code compile successfully? (1 correct answer)

    class Test <T> {
    T instance;
    Test(T instance) {
        this.instance = instance;
    }
    }
    

    1. Yes.
    2. No.
66. Will this code compile successfully? (1 correct answer)

    class Test <T> {
    Test(T my) {
        boolean b = (my instanceof T);
    }
    }
    

    1. Yes.
    2. No.
67. Will this code compile successfully? (1 correct answer)

    class Test <T> {
    void test(T method) {
        Object my = (T)method;
    }
    }
    

    1. Yes.
    2. No.
68. Will this code compile successfully? (1 correct answer)

    class Test <T> {
    void test() {
        NavigableMap map = new TreeMap<String, T>();
    }
    }
    

    1. Yes.
    2. No.
69. Will this code compile successfully? (1 correct answer)

    class Test <T> {
    private T[] array = null;
    }
    

    1. Yes.
    2. No.
70. Will this code compile successfully? (1 correct answer)

    class Test <T> {
    private T[] array = new T[7];
    }
    

    1. Yes.
    2. No.
71. Will this code compile successfully? (1 correct answer)

    class Test<String> {
        String my = "Hello!";
    }
    

    1. Yes.
    2. No.
72. Will this code compile successfully? (1 correct answer)

    class Test<String> {
        String my;
        public Test(String my) {
            this.my = my;
        }
        public String get() {
            return my;
        }
    }
    
    public class RunTest {
        public static void main(String[] args) {
            Integer i = new Test<Integer>(1).get();
            System.out.println(i.getClass());
        }
    }
    

    1. Yes.
    2. No.

© 2008 Nikos Pougounias. This is a free contribution to the Javacommunity. Please distribute it for free. https://nikojava.wordpress.com

Answers

1. b
2. b
3. a
4. b
5. b
6. a
7. b
8. b
9. b
10. b
11. b
12. b
13. b
14. b
15. a
16. b
17. a
18. b
19. a
20. b
21. a
22. b
23. a
24. a
25. a
26. a
27. b
28. a
29. b
30. b
31. a
32. b
33. b
34. a
35. b
36. a
37. a
38. b
39. b
40. a
41. a
42. b
43. a
44. a
45. a
46. a
47. c
48. b
49. b
50. b
51. b
52. a
53. b
54. a
55. b
56. b
57. a
58. b
59. b
60. a
61. a
62. a
63. a
64. b
65. a
66. b
67. a
68. a
69. a
70. b
71. b
72. a