public class Car extends Vehicle implements Drivable {}
public class Truck extends Vehicle implements Drivable {}
public class Tank implements Drivable {}
发生编译时错误的一组代码是:
A.
Car car = new Car(); Vehicle vehicle = car;
B.
Tank tank = new Tank(); Vehicle vehicle = tank;
C.
Drivable drivable = new Tank(); Object o = drivable;
D.
Vehicle vehicle = new Vehicle(); Object o = vehicle;
答案 B
11.(0.0分)下列语句输出的结果是( )。 var foo = "ABCDE"; foo.substring(3); foo.concat("XYZ"); System.out.println(foo);
A.
ABCDE
B.
DEXYZ
C.
XYZ
D.
DE
答案 A
12.(0.0分)给定下面程序段,输出结果为()。 int i
=
1, j
=
0 ; switch(i){ case 1 -> j
+=
6; case 2 -> j
+=
1; default -> j
+=
2;
}
System.out.println(j);
A.
2
B.
6
C.
7
D.
9
答案 B
13.(0.0分)有下列一段代码,下面哪些语句可以确定“cat”包含在列表list中?( )
ArrayList<String> list = new ArrayList<>();
list.add("dog");
list.add("cat");
list.add("horse");
A.
list.contains("cat")
B.
list.hasObject("cat")
C.
list.indexOf("cat")
D.
list.indexOf(1)
答案 A
14.(0.0分)要使一个类能够序列化,需要具备的条件是( )。
A.
继承ObjectStream类
B.
具有带参数构造方法
C.
实现Serializable接口
D.
定义了writeObject()方法
答案 C
15.(0.0分)下面程序运行结果为( )。 class Alpha { String getType() { return "alpha"; } } class Beta extends Alpha { String getType() { return
"beta"; } } class Gamma extends Beta { String getType() { return "gamma"; } public static void main(String[] args) { Alpha g1 = new Beta();
Alpha g2
=
new Gamma(); System.out.println(g1.getType()
+
" "
+
g2.getType());
} }
A.
alpha alpha
B.
gamma gamma
C.
alpha beta
D.
beta gamma
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