类 Teacher 和 Student 是类 Person 的子类; Teacher t; Student s; // t and s are all non-null. if （t instanceof Person ){ s=（Student)t; } 最后一条语句的结果是:A．将构造一个Student 对象;B．表达式是合法的；C．表达式是错误的；D．编译时正确， 但运行时错误。
类 Teacher 和 Student 是类 Person 的子类; Teacher t; Student s; // t and s are all non-null. if （t instanceof Person ){ s=（Student)t; } 最后一条语句的结果是:
A．将构造一个Student 对象;
B．表达式是合法的；
C．表达式是错误的；
D．编译时正确， 但运行时错误。
参考答案和解析
编译时正确,但运行时错误
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