面向对象编程题目.doc

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1、面向对象编程(1)Given the following Java code:class Animal public String noise () return peep class Dog extends Animal public String noise () return back; class Cat extends Animal public String noise () return move; . . . Animal animal = new Dog();Cat cat = ( Cat ) animal;System.out.printIn( cat.noise() )

2、;What is the result? A. peepB. backC. moveD. Compilation fails.E. An exception is thrown at runtime (2)Given the following Java code:10.11.12.13.14.15.16.interface A public int getValue (); class B implements A public int getValue () return 1; class C extends B / insert code hereWhat three code frag

3、ments inserted individually at line 15, make used 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(); (3)Add methods t

4、o the Beta class to make it compile correctly. class Alpha public void bar ( int x ) public void bar (int x ) public class Beta extends Alpha place here place here place here Methodsprivate void bar ( int x ) public void bar ( int x ) public int bar ( String x ) return 1; public Alpha bar ( int x )

5、public void bar ( int x, int y ) public int bar ( int x ) return x; (4)Given the following Java code:class Test1public Test1 foo() return this; class Test2 extends Test1 public Test1 foo() return this; class Test3 extends Test2 / insert method hereWhich two methods, inserted individually, correctly

6、complete the Test3 class?(choose two) A. public void foo() B. public int foo() return 3; C. public Test2 foo() return this; D. public Test1 foo() return this; (5)Given the following Java code:public class Bootchyint bootch;String snootch;public Bootchy() this( snootchy );System.out.print( first ) ;p

7、ublic Boothchy( String snootch ) this( 420, snootchy );System.out.print( second ) ;public Bootchy(int bootch, String snootch ) this.bootch = bootch;this. snootch = snootch;System.out.print( third );public static void main(String args ) Bootchy b= new Bootchy ();System.out.print(b.snootch + + b.bootc

8、h );What is the result? (运行结果)(6)Given the following Java code: 09.10.11.12.13.14.15.16.17.18.19.20.21.public class Teststatic class A void process () throws Exception throw new Exception () ; static class B extends A void process () System.out.println( B ); public static void main (String args ) A

9、a = new B ();a.process ();What is the result?A. BB. The code exception is thrown at runtime (执行时抛出exception)C. The code run with no output (沒有任何输出)D. Compilation fails because of an error in line 15. E. Compilation fails because of an error in line 18. F. Compilation fails because of an error in lin

10、e 19. (7)Given the following Java code:1011.12.13.14.15.16.17.18.interface Foo class Alpha implements Foo class Beta extends Alpha class Delta extends Beta public static void main(String args) Beta x = new Beta ();/ insert code hereWhich code, inserted at line 16 will cause a java.lang.ClassCastExce

11、ption?A. Alpha a = x;B. Foo f = (Delta)x;C. Foo f = (Alpha)x;D. Beta b = (Beta)(Alpha)x;(8)Given the following Java code:public class Personprivate String name, comment;private int age;public Person(String n, int a, String c) name = n; age = a; comment = c;public Boolean equals(Object o)if (! (o ins

12、tanceof Person) return false;Person p = (Person)o;return age = p.age & name.equals(p.name);What is the appropriated definition of the hashCode method in class Person? A. return super.hashCode();B. return name.hashCode()+age*7;C. return namehashcode() + comment.hashCode()/2;D. return name.hashCode()

13、+ comment.hashCode()/2 - age*3;(9)Given the following code:01.02.03.04.05.06.07.public class Personprivate String name;public Person (String name) this.name = name; public Boolean equals(Person p)return p.name.equals(this.name);Which statement is true? A. The equals method does NOT properly override

14、 the object Object.equals method. B. Compilation fails because the private attribute p.name cannot be accessed in line 5. C. To work correctly with hash-based data structures, this class must also implement the hashCode method. D. When adding Person objects to java.util. Set collection, the equals m

15、ethod in line 4 will prevent duplicates.(10)Place the Output Options in the Actual Output Sequence to indicate the output from this code: class Alpha public void foo(String. args) System.out.print(Alpha:foo );public void bar(String a) System.out.print(Alpha:bar );public class Beta extends Alpha publ

16、ic void foo(String a) System.out.print(Beta:foo );public void bar(String a) System.out.print(Beta:bar );public static void main(String args) Alpha a = new Beta();Beta b = (Beta)a;a.foo(test);b.foo(test);a.bar(test);b.bar(test);Actul Output Sequence: Place herePlace here Place here Place here Output

17、Option: Alpha:fooAlpha:bar Beta:foo Beta:bar (11)Given the following Java code:1.2.3.public interface A public void doSomething(String thing);1.2.3.public class AImp1 implements A public void doSomething(String msg) 1.2.3.4.5.6.7.8.9.public class B public A doit() / more code here public String exec

18、ute() / more code here1.2.3.4.5.6.7.8.9.public class C extends B public AImp1 doit() / more code here public Object execute() / more code hereWhich statement is true about the class and interfaces in this Code? A. Compilation will succeed for all classes and interfaces. B. Compilation of class C wil

19、l fail because of an error int line 2.C. Compilation of class C will fail because of an error int line 6. D. Compilation of AImpl will fail because of an error in line 2. (12)Given the following Java code:class A String name = A ;String getName() return name;String greeting() return class A ;class B

20、 extends A String name = B ;String greeting() return class B ;public class Client public static void main(String args) A a = new A() ;A b = new B() ;System.out.println(a.greeting () + has name + a.getName () ) ;System.out.println(b.greeting () + has name + b.getName () ) ;Place the names A and B in

21、the following output.Class Place here has name Place here Class Place here has name Place hereNames:AB (13)Given the following Java code: 1.2.3.4.5.6.7.8.9.10.class SuperClass public A getA() return new A() ;class SubClass extends SuperClass public B getA() return new B();Which statement is true ? A

22、. Compilation will succeed if A extends B B. Compilation will succeed if B extends AC. Compilation will always fail because of an error in line 7 D. Compilation will always fail because of an error in line 8(14)Given the following Java code: 1.2.3.4.5.6.7.8.9.10.11.12.13.14.15.class Pizza java.util.

23、ArrayList toppings;public final void addTopping(String topping) toppings.add(topping);public class PepperoniPizza extends Pizza public void addTopping(String topping) System.out.println(Cannot and Uoppings);public static void main(String args) Pizza pizza = new PepperoniPizza();Pizza.addTopping(Mush

24、rooms);What is the result ? A. Compilation fails B. Cannot and UoppingsC. The code runs with no outputD. A NullPointerException is thrown in Line 4(15)Given the following Java code:10.11.12.13.14.15.16.17.18.19.interface A void x ();class B implements A public void x () public void y () class C exte

25、nds B public void x () And :20.21.22.23.24.25.26.java.util.List list = new java.util.ArrayList ();list.add(new B ();list.add(new C ();for (A a : list ) a.x();a.y();What is the result ? A. The code runs with no output B. An exception thrown at runtime C. Compilation fails because of an error in line

26、20D. 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(16)Given the following Java code:10.11.12.13.14.15.class One void foo() class Two extends One / insert method hereWhich three methods, inserte

27、d individually at line 14 will correctly class Two ?(Choose three) A. int foo()/*more code here */B. void foo()/*more code here */C. public void foo()/*more code here*/D. private void foo()/*more code here*/E. protected void foo()/*more code here*/(17)Which two statements are true about the hashCode

28、 method? (Choose two)A. The hashCode method for a given class can be used to test for object equality and object inequality for that class. (hashCode method B. The hashCode method is used by the java.util.SortedSet collection class to order the ements within that set. C. The hashCode method for a gi

29、ven class can be used to test for object inequality, but NOT object equality for that class. D. The only important characteristic of the values returned by a hashCode method is that distribution of values must follow a Gaussian distribution.E. The hashCode method is used by the java.util.HashSet col

30、lection class to group the elements within that set into hash buckets for swift retrieval. (18)Given the following Java code:class SomeException:public class SomeException class A:public class A public void doSomething() class B:public vlass B extends A public void soSomething() throws SomeException Which statement is true about the two classes? A. Compilation of both classes will fail. B. Compilation of both classes will succeed. C. Compilation of class A will fail, Compilation of class B will succeed.D. Compilation of class B will fail, Compilation of class A will succeed.