多项选择题

Which four are true？（）

A. Has-a relationships should never be encapsulated.
B. Has-a relationships should be implemented using inheritance.
C. Has-a relationships can be implemented using instance variables.
D. Is-a relationships can be implemented using the extends keyword.
E. Is-a relationships can be implemented using the implements keyword.
F. An array or a collection can be used to implement a one-to-many has-a relationship.
G. The relationship between Movie and Actress is an example of an is-a relationship.

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多项选择题

public class Team extends java.util.LinkedList {
public void addPlayer（Player p） {
add（p）；
}
public void compete（Team opponent） { /* more code here */ }
}
class Player { /* more code here */ }
Which two are true？（）

A. This code will compile.
B. This code demonstrates proper design of an is-a relationship.
C. This code demonstrates proper design of a has-a relationship.
D. A Java programmer using the Team class could remove Player objects from a Team object.

单项选择题

10. public class SuperCaic {
11. protected static int multiply（int a， int b） { return a * b； }
12. }
and：
20. public class SubCalc extends SuperCalc {
21. public static int multiply（int a， int b） {
22. int c = super.multiply（a， b）；
23. return c；
24. }
25. }
and：
30. SubCalc sc = new SubCalc（）；
31. System.out.println（sc.multiply（3，4））；
32. System.out.println（SubCalc.multiply（2，2））；
What is the result？（）

A. 12 4
B. The code runs with no output.
C. An exception is thrown at runtime.
D. Compilation fails because of an error in line 21.
E. Compilation fails because of an error in line 22.
F. Compilation fails because of an error in line 31.

单项选择题

public class Foo {
public int a；
public Foo（） { a = 3； }
public void addFive（） { a += 5； }
}
and：
public class Bar extends Foo {
public int a；
public Bar（） { a = 8； }
public void addFive（） { this.a +=5； }
}
invoked with：
Foo foo = new Bar（）；
foo.addFive（）；
System.out.println（”Value： “+ foo.a）；
What is the result？（）

A. Value： 3
B. Value： 8
C. Value： 13
D. Compilation fails.
E. The code runs with no output.
F. An exception is thrown at runtime.