日期:2014-05-20  浏览次数:20640 次

帮忙解答下这题。。。。
求讲解 谢谢了
Question No: 5
interface MyInterface{}
public class MyInstanceTest implements MyInterface{
static String s;
public static void main(String args[]){
MyInstanceTest t = new MyInstanceTest();
if(t instanceof MyInterface){
System.out.println("I am true interface");
}else {
System.out.println("I am false interface");
}
if(s instanceof String){
System.out.println("I am true String");
}else {
System.out.println("I am false String");
}
}
}
A.compile time error
B.runtime error
C.prints: “I am true interface” followed by “I am true String”
D.prints: “I am true interface” followed by “I am false String”
E.prints: “I am false interface” followed by “I am false String”
F.prints: “I am false interface” followed by “I am true String”


------解决方案--------------------
虽然格式很乱,但是还是耐着性子看到了if(s instanceof String)这一行,编译错误,A

没有继承、实现关系的类是无法instanceof的
------解决方案--------------------
D s 被初始化为 null。 null instanceof XXX 总是 false