SCJP Questions 141-150

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Question 141
Given:
10. abstract class A {
11. abstract void al();
12. void a2() { }
13. }
14. class B extends A {
15. void a1() { }
16. void a2() { }
17. }
18. class C extends B { void c1() { } }
and:
A x = new B(); C y = new C(); A z = new C();
Which four are valid examples of polymorphic method calls? (Choose
four.)
A. x.a2();
B. z.a2();
C. z.c1();
D. z.a1();
E. y.c1();
F. x.a1();
Answer: ABDF

Question 142
Given:
10. interface A { void x(); }
11. class B implements A { public void x() { } public voidy() { } }
12. class C extends B { public void x() {} }
And:
20. java.util.List<A> list = new java.util.ArrayList<A>();
21. list.add(new B());
22. list.add(new C());
23. for (A a:list) {
24. a.x();
25. a.y();;
26. }
What is the result?
A. The code runs with no output.
B. An exception is thrown at runtime.
C. Compilation fails because of an error in line 20.
D. Compilation fails because of an error in line 21.
E. Compilation fails because of an error in line 23.
F. Compilation fails because of an error in line 25.
Answer: F

Question 143
Given:
1. class SuperClass {
2. public A getA() {
3. return new A();
4. }
5. }
6. class SubClass extends SuperClass {
7. public B getA() {
8. return new B();
9. }
10. }
Which is true?
A. Compilation will succeed if A extends B.
B. Compilation will succeed if B extends A.
C. Compilation will always fail because of an error in line 7.
D. Compilation will always fail because of an error in line 8.
Answer: B

Question 144
Given:
1. interface A { public void aMethod(); }
2. interface B { public void bMethod(); }
3. interface C extends A,B { public void cMethod(); }
4. class D implements B {
5. public void bMethod() { }
6. }
7. class E extends D implements C {
8. public void aMethod() { }
9. public void bMethod() { }
10. public void cMethod() { }
11. }
What is the result?
A. Compilation fails because of an error in line 3.
B. Compilation fails because of an error in line 7.
C. Compilation fails because of an error in line 9.
D. If you define D e = new E(), then e.bMethod() invokes the version
of bMethod() defined in Line 5.
E. If you define D e = (D)(new E()), then e.bMethod() invokes the
version of bMethod() defined in Line 5.
F. If you define D e = (D)(new E()), then e.bMethod() invokes the
version of bMethod() defined in Line 9.
Answer: F

Question 145
Given:
10. interface A { public int getValue() }
11. class B implements A {
12. public int getValue() { return 1; }
13. }
14. class C extends B {
15. // insert code here
16. }
Which three code fragments, inserted individually at line 15, make use
of polymorphism? (Choose three.)
A. public void add(C c) { c.getValue(); }
B. public void add(B b) { b.getValue(); }
C. public void add(A a) { a.getValue(); }
D. public void add(A a, B b) { a.getValue(); }
E. public void add(C c1, C c2) { c1.getValue(); }
Answer: BCD

Question 146
Given:
1. class ClassA {
2. public int numberOfinstances;
3. protected ClassA(int numberOfinstances) {
4. this.numberOflnstances = numberOfinstances;
5. }
6. }
7. public class ExtendedA extends ClassA {
8. private ExtendedA(int numberOfinstances) {
9. super(numberOflnstances);
10. }
11. public static void main(String[] args) {
12. ExtendedA ext = new ExtendedA(420);
13. System.out.print(ext.numberOflnstances);
14. }
15. }
Which is true?
A. 420 is the output.
B. An exception is thrown at runtime.
C. All constructors must be declared public.
D. Constructors CANNOT use the private modifier.
E. Constructors CANNOT use the protected modifier.
Answer: A

Question 147
147. Given:
1. public class Base {
2. public static final String FOO = “foo”;
3. public static void main(String[] args) {
4. Base b = new Base();
5. Sub s = new Sub();
6. System.out.print(Base.FOO);
7. System.out.print(Sub.FOO);
8. System.out.print(b.FOO);
9. System.out.print(s.FOO);
10. System.out.print(((Base)s).FOO);
11. } }
12. class Sub extends Base {public static final String FOO=bar;}
What is the result?
A. foofoofoofoofoo
B. foobarfoobarbar
C. foobarfoofoofoo
D. foobarfoobarfoo
E. barbarbarbarbar
F. foofoofoobarbar
G. foofoofoobarfoo
Answer: D

Question 148
Which three statements are true? (Choose three.)
A. A final method in class X can be abstract if and only if X is abstract.
B. A protected method in class X can be overridden by any subclass of
X.
C. A private static method can be called only within other static
methods in class X.
D. A non-static public final method in class X can be overridden in any
subclass of X.
E. A public static method in class X can be called by a subclass of X
without explicitly referencing the class X.
F. A method with the same signature as a private final method in class
X can be implemented in a subclass of X.
G. A protected method in class X can be overridden by a subclass of A
only if the subclass is in the same package as X.
Answer: BEF

Question 149
Given:
1. class Pizza {
2. java.util.ArrayList toppings;
3. public final void addTopping(String topping) {
4. toppings.add(topping);
5. }
6. }
7. public class PepperoniPizza extends Pizza {
8. public void addTopping(String topping) {
9. System.out.println(”Cannot add Toppings”);
10. }
11. public static void main(String[] args) {
12. Pizza pizza = new PepperoniPizza();
13. pizza.addTopping(”Mushrooms”);
14. }
15. }
What is the result?
A. Compilation fails.
B. Cannot add Toppings
C. The code runs with no output.
D. A NullPointerException is thrown in Line 4.
Answer: A

Question 150
Given:
1. class Super {
2. private int a;
3. protected Super(int a) { this.a = a; }
4. }
.....
11. class Sub extends Super {
12. public Sub(int a) { super(a); }
13. public Sub() { this.a= 5; }
14. }
Which two, independently, will allow Sub to compile? (Choose two.)
A. Change line 2 to:
public int a;
B. Change line 2 to:
protected int a;
C. Change line 13 to:
public Sub() { this(5); }
D. Change line 13 to:
public Sub() { super(5); }
E. Change line 13 to:
public Sub() { super(a); }
Answer: CD

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