java,关于Abstract一些题

1  Which of the following class definitions defines a legal abstract class?
A. class A { abstract void unfinished() { } }
B. class A { abstract void unfinished(); }
C. abstract class A { abstract void unfinished(); }
D. public class abstract A { abstract void unfinished(); }

2  Which of the following declares an abstract method in an abstract Java class?
A. public abstract method();
B. public abstract void method();
C. public void abstract Method();
D. public void method() {}
E. public abstract void method() {}

3  Which of the following statements regarding abstract methods are true?
A. An abstract class can have instances created using the constructor of the abstract class.
B. An abstract class can be extended.
C. A subclass of a non-abstract superclass can be abstract.
D. A subclass can override a concrete method in a superclass to declare it abstract.
E. An abstract class can be used as a data type.

4  Which of the following statements regarding abstract methods are true?
A. Abstract classes have constructors.
B. A class that contains abstract methods must be abstract.
C. It is possible to declare an abstract class that contains no abstract methods.
D. An abstract method cannot be contained in a nonabstract class.
E. A data field can be declared abstract.

5  Suppose A is an abstract class, B is a concrete subclass of A, and both A and B have a default constructor. Which of the following is correct?
A. A a = new A();
B. A a = new B();
C. B b = new A();
D. B b = new B();

6  What is the output of running class Test?

public class Test {
public static void main(String[] args) {
new Circle9();
}
}

public abstract class GeometricObject {
protected GeometricObject() {
System.out.print("A");
}

protected GeometricObject(String color, boolean filled) {
System.out.print("B");
}
}

public class Circle9 extends GeometricObject {
/** Default constructor */
public Circle9() {
this(1.0);
System.out.print("C");
}

/** Construct circle with a specified radius */
public Circle9(double radius) {
this(radius, "white", false);
System.out.print("D");
}

/** Construct a circle with specified radius, filled, and color */
public Circle9(double radius, String color, boolean filled) {
super(color, filled);
System.out.print("E");
}
}

A. ABCD
B. BACD
C. CBAE
D. AEDC
E. BEDC