单选题

期中小测错题

1. Which specifier essentially declares a variable a global variable?

A. protected

B. static

C. final

D. default

 2. What code may be filled in the blank without causing syntax or runtime errors ？

public class Test {
  java.util.Date date;
  public static void main(String[] args) {
    Test test = new Test();
    System.out.println(_________________);
  }
}

A. test.date

B. date

C. test.date.toString()

D. date.toString()

 3. 关于被保护访问控制符protected修饰的成员变量,以下说法正确的是：

A. 可以被三种类所引用:该类自身、与它在同一个包中的其他类、在其他包中的该类的子类

B. 可以被两种类访问和引用:该类本身、该类的所有子类

C. 只能被该类自身所访问和修改

D. 只能被同一个包中的类访问

 4. Which of the following statements are not true ？

A. A default constructor is provided automatically if no constructors are explicitly declared in the class

B. At least one constructor must always be defined explicitly

C. The default constructor is a no-arg constructor

D. A default constructor always exist in class

 5. What will happen when you attempt to compile and run the following code?

class Base{
Base(){
        System.out.println("Base");
        }
}

public class Checket extends Base{
public static void main(String argv[]){
        Checket c = new Checket();
        super();
        }

Checket(){
        System.out.println("Checket");  
        }       
}

A. Compile time error

B. Checket followed by Base

C. Base followed by Checket

D. runtime error

 6.  What is the output of running class C?

class A {
  public A() {
    System.out.println(
      "The default constructor of A is invoked");
  }
}

class B extends A {
  public B() {
    System.out.println(
      "The default constructor of B is invoked");
  }
}

public class C  {
  public static void main(String[] args) {
    B b = new B();
  }
}

A. Nothing displayed

B. "The default constructor of B is invoked"

C. "The default constructor of A is invoked""The default constructor of B is invoked"

D. "The default constructor of B is invoked""The default constructor of A is invoked"