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() ) ;

What is the result?  

A. peep
B. back
C. move
D. Compilation fails.
E. An exception is thrown at runtime

Given the following Java code:

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interface A { public int getValue (); }
class B implements A {

public int getValue () { return 1; }

}
class C extends B {

// insert code here

}

What three code fragments 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(); }

Add methods to 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

}

Methods

private void bar ( int x ) {}

public void bar ( int x ) {}

public int bar ( String x ) { return 1; }

public Alpha bar ( int x ) {}

public void bar ( int x, int y ) {}

public int bar ( int x ) { return x; }

Given the following Java code:

class Test1{

public Test1 foo() { return this; }

}
class Test2 extends Test1 {

public Test1 foo() { return this; }

}
class Test3 extends Test2 {

// insert method here

}

Which two methods, inserted individually, correctly 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; }

Given the following Java code:

public class Bootchy{

int bootch;

String snootch;

public Bootchy() {

this( "snootchy" );

System.out.print( "first " ) ;

}

public 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.bootch );

}

}

What is the result? (运行结果)

Given the following Java code:

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public class Test{

static 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 a = new B ();

a.process ();

}

}

What is the result?

A. B
B. 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 line 19.

Given the following Java code:

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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 here

}

}

Which code, inserted at line 16 will cause a java.lang.ClassCastException?

A. Alpha a = x;
B. Foo f = (Delta)x;
C. Foo f = (Alpha)x;
D. Beta b = (Beta)(Alpha)x;

Given the following Java code:

public class Person{

private 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 instanceof 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() + comment.hashCode()/2 - age*3;

Given the following code:

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public class Person{

private 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 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 method in line 4 will prevent duplicates.

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 {

public 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:

Output Option:

Given the following Java code:

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public interface A {

public void doSomething(String thing);

}

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public class AImp1 implements A {

public void doSomething(String msg) {}

}

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public class B {

public A doit() {

// more code here

}

public String execute() {

// more code here

}

}

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public class C extends B {

public AImp1 doit() {

// more code here

}

public Object execute() {

// more code here

}

}

Which 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 will 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.

Given the following Java code:

class A {

String name = "A" ;

String getName() {

return name;

}

String greeting() {

return "class A" ;

}

}
class B 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 the following output.
Class Place here has name Place here 
Class Place here has name Place here

Names:

Given the following Java code:

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class SuperClass {

public A getA() {

return new A() ;

}

}
class SubClass extends SuperClass {

public B getA() {

return new B();

}

}

Which statement 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

Given the following Java code:

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class Pizza {

java.util.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("Mushrooms");

}

}

What is the result ?  

A. Compilation fails
B. Cannot and Uoppings
C. The code runs with no output
D. A NullPointerException is thrown in Line 4

Given the following Java code:

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interface A {

void x ();

}
class B implements A {

public void x () {}

public void y () {}

}
class C extends B {

public void x () {}

}

And :

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java.util.List <A> list = new java.util.ArrayList<A> ();

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 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

Given the following Java code:

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class One {

void foo() {}

}
class Two extends One {

// insert method here

}

Which three methods, inserted 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*/}

Which two statements are true about the hashCode 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 given 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 collection class to group the elements within that set into hash buckets for swift retrieval.

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.