SCJP程序员认证考试单项选择题每日一练(2020.06.09)

单项选择题
10. interface Foo {} 11. class Alpha implements Foo {} 12. class Beta extends Alpha {} 13. class Delta extends Beta { 14. public static void main（ String[] args） { 15. Beta x = new Beta（）； 16. // insert code here 17. } 18. } Which code， inserted at line 16， will cause a java.lang.ClassCastException？（）
A. Alpha a = x；
B. Foo f= （Delta）x；
C. Foo f= （Alpha）x；
D. Beta b = （Beta）（Alpha）x；
单项选择题
What is the result？（）
A.1
B.12
C.14
D.123
E.Compilation fails.
F.An exception is thrown at runtime.
单项选择题
When line 14 is reached， how many objects are eligible for the garbage collector？（）
A.0
B.1
C.2
D.3
E.4
F.6
单项选择题
55. int []x= {1， 2，3，4， 5}； 56. int y[] =x； 57. System.out.println（y[2]）； Which is true？（）
A. Line 57 will print the value 2.
B. Line 57 will print the value 3.
C. Compilation will fail because of an error in line 55.
D. Compilation will fail because of an error in line 56.
单项选择题
public class test（ public static void main（string[]args）{ string foo = args [1]； string foo = args [2]； string foo = args [3]； } ） And command line invocation： Java Test red green blue What is the result？（）
A. Baz has the value of “”
B. Baz has the value of null
C. Baz has the value of “red”
D. Baz has the value of “blue”
E. Bax has the value of “green”
F. The program throws an exception.