Question 27: To determine if you can invoke addContainerListener() for a component referenced using a variable named c, which expression(s) can you evaluate that will give you a true or false answer to this questions?
Select all valid answers.
a) c == Container
b) c.equals(Class.Container)
c) c instanceof Container
d) c instanceof Component
e) c implements Container
answer
--------------------------------------------------------------------------------Question 28: Write a statement for a constructor that invokes the no-args, default constructor in its superclass.
Fill in the blank
Answer---------------这个是填空题,
看不大懂,请大家帮帮忙,谢谢!
Select all valid answers.
a) c == Container
b) c.equals(Class.Container)
c) c instanceof Container
d) c instanceof Component
e) c implements Container
answer
--------------------------------------------------------------------------------Question 28: Write a statement for a constructor that invokes the no-args, default constructor in its superclass.
Fill in the blank
Answer---------------这个是填空题,
看不大懂,请大家帮帮忙,谢谢!
写一个构造函数,调用其父类的无参数构造函数Super();
c肯定是正确的,第二个:
public MyClass(){
super();
}
d) c instanceof Component望Swing达人指正
c) c instanceof Container
d) c instanceof Component Question 28 key :
super()
所以用 instanceof 的时候得到的是 true例:
class A{
}class B extends A{
}
public class Test{ public static void main(String[] args) {
B b = new B();
if (b instanceof B) System.out.println("ok1");
if (b instanceof A) System.out.println("ok2");
}
}
Component 可以addContainerListener()吗?
所以c和d都对
referenced using a variable named c, which expression(s) can you evaluate that will
give you a true or false answer to this questions?
Select all valid answers.
a) c == Container
b) c.equals(Class.Container)
c) c instanceof Container
d) c instanceof Component
e) c implements Container问题 27:有一个名子为C的组件(component),是否可以对这个组件调用addContainerListener()方法?下面的哪个(一个或者多个)表达式能够解决上面的问题,并且对这个问题给出“是”或者“否”的答案。
选择所有的答案。
a)c == Container
b)c.equals(Class.Container)
c)c instanceof Container
d)c instanceof Component
e)c implements Container其实如果一个组件(component)是Container的子类就可以调用addContainerListener()方法。所以关键是5个选项中,哪个能判断出来c是Container的子类。