Java题库——Chapter5

Posted 2022-11-26 wkfvawl

1)Suppose your method does not return any value, which of the following keywords can be used as a return type?
A)void  B)public  C)int  D)double  E)None of the above

2)The signature（函数签名） of a method consists of ________.  
A)method name and parameter list
B)parameter list
C)return type, method name, and parameter list
D)method name  

3)All Java applications must have a method ________.   
A)public static Main(String args[ ])
B)public static void main(String[ ] args)
C)public static Main(String[ ] args)
D)public static main(String[ ] args)
E)public void main(String[ ] args)

4)Arguments to methods always appear within ________.
A)parentheses  B) quotation marks  C)curly braces  D) brackets

parentheses 括号 函数的参数出现在括号中

　　
5)Does the return statement in the following method cause compile errors?

public static void main(String[ ] args) 
  int max = 0;
  if (max != 0)
    System.out.println(max);
  else
    return;

A)Yes B) No

6)Does the method call in the following method cause compile errors?

public static void main(String[ ] args) 
  Math.pow(2, 4);

A)Yes B) No

7)Each time a method is invoked, the system stores parameters and local variables in an area of memory, known as ________, which stores elements in last-in first-out fashion.
A)a stack  B) a heap  C)an array  D) storage area

8)Which of the following should be declared as a void method?   
A)Write a method that prints integers from 1 to 100.
B)Write a method that converts an uppercase letter to lowercase.
C)Write a method that checks whether current second is an integer from 1 to 100.
D)Write a method that returns a random integer from 1 to 100.

注意题目要求是没有返回值void类型的

9)When you invoke a method with a parameter, the value of the argument is passed to the parameter. This is referred to as ________.
A)pass by reference  B) pass by value  C)pass by name  D) method invocation

值传递

10)Given the following method

static void nPrint(String message, int n) 
  while (n > 0) 
    System.out.print(message);
    n--;
  

What is the printout of the call nPrint(‘a‘, 4)?  
A)invalid call  B) aaaa  C)aaaaa  D) aaa

‘a‘是char类型

The method nPrint(String, int) in the type test is not applicable for the arguments (char, int)

11)Given the following method

static void nPrint(String message, int n) 
  while (n > 0) 
    System.out.print(message);
    n--;
  

What is k after invoking nPrint("A message", k)?
int k = 2;
nPrint("A message", k);
A)2 B) 1 C) 0 D) 3

这里的传递方式是值传递，并不会改变实参的值。

12)Analyze the following code:

public class Test 
  public static void main(String[ ] args) 
    System.out.println(xMethod(5, 500L));
  
  public static int xMethod(int n, long l) 
    System.out.println("int, long");
    return n;
  
  public static long xMethod(long n, long l) 
    System.out.println("long, long");
    return n;
  
 

A)The program runs fine but displays things other than 5.
B)The program displays long, long followed by 5.
C)The program displays int, long followed by 5.
D)The program does not compile because the compiler cannot distinguish which xmethod to invoke.

13)Analyze the following code:

class Test 
  public static void main(String[ ] args) 
    System.out.println(xmethod(5));
  
  public static int xmethod(int n, long t) 
    System.out.println("int");
    return n;
  
  public static long xmethod(long n) 
    System.out.println("long");
    return n;
  

A)The program runs fine but displays things other than 5.
B)The program displays int followed by 5.
C)The program displays long followed by 5.
D)The program does not compile because the compiler cannot distinguish which xmethod to invoke.

14)Analyze the following code.

public class Test 
  public static void main(String[ ] args)  
    System.out.println(max(1, 2));  
  
  public static double max(int num1, double num2) 
    System.out.println("max(int, double) is invoked");
    if (num1 > num2)
      return num1;
    else
      return num2;
  
  public static double max(double num1, int num2) 
    System.out.println("max(double, int) is invoked");
    if (num1 > num2)
      return num1;
    else
      return num2;     
  

A)The program runs and prints 2 followed by "max(int, double)" is invoked.
B)The program runs and prints 2 followed by "max(double, int)" is invoked.
C)The program cannot compile because the compiler cannot determine which max method should be invoked.
D)The program runs and prints "max(int, double) is invoked" followed by 2.
E)The program cannot compile because you cannot have the print statement in a non-void method.

15)Analyze the following code.

public class Test 
  public static void main(String[ ] args)  
    System.out.println(m(2));  
  
  public static int m(int num) 
    return num;
  
  public static void m(int num) 
    System.out.println(num);
  

A)The program has a compile error because the two methods m have the same signature.
B)The program runs and prints 2 twice.
C)The program runs and prints 2 once.
D)The program has a compile error because the second m method is defined, but not invoked in the main method.

16)What is k after the following block executes?

  int k = 2;
  nPrint("A message", k);

System.out.println(k);

A)2  B)1  C)0  D)k is not defined outside the block. So, the program has a compile error

17)A variable defined inside a method is referred to as ________.   
A)a method variable  B) a global variable  C)a block variable  D) a local variable

18)The client can use a method without knowing how it is implemented. The details of the implementation are encapsulated in the method and hidden from the client who invokes the method. This is known as ________. (Choose all that apply.)
A)encapsulation  B) information hiding  C)simplifying method  D) method hiding

封装和信息隐藏

19)Which of the following is a possible output from invoking Math.random()? (Choose all that apply.)
A)1.0 B) 0.5 C) 3.43 D) 0.0

20)What is Math.round(3.6)?
A)4 B) 3 C) 4.0 D) 3.0

Math.round四舍五入取整

21)What is Math.rint(3.6)?
A)3.0 B) 5.0 C) 4.0 D) 3

Math.rint返回最接近这个数的整数,如果刚好居中，则取偶数 

22)What is Math.rint(3.5)?
A)3.0 B) 3 C) 5.0 D) 4.0 E) 4

23)What is Math.ceil(3.6)?
A)5.0 B) 3.0 C) 3 D) 4.0

Math.ceil向上取整

24)What is Math.floor(3.6)?
A)4 B) 3.0 C) 3 D) 5.0

Math.floor向下取整

25)(int)(Math.random() * (65535 + 1)) returns a random number ________.
A)between 1 and 65536  B) between 0 and 65535  
C)between 1 and 65535  D) between 0 and 65536

26)(int)(‘a‘ + Math.random() * (‘z‘ - ‘a‘ + 1)) returns a random number ________.   
A)between ‘a‘ and ‘z‘ B) between 0 and (int)‘z‘ C)between ‘a‘ and ‘y‘ D) between (int)‘a‘ and (int)‘z‘

注意这里的类型是int！

27)(char)(‘a‘ + Math.random() * (‘z‘ - ‘a‘ + 1)) returns a random character ________.
A)between ‘b‘ and ‘y‘ B) between ‘b‘ and ‘z‘ C)between ‘a‘ and ‘z‘ D) between ‘a‘ and ‘y‘

28)Which of the following is the best for generating random integer 0 or 1?   
A)(int)Math.random() + 1
B)(int)(Math.random() + 0.8)
C)(int)(Math.random() + 0.2)
D)(int)Math.random()
E)(int)(Math.random() + 0.5)

29)________ is to implement one method in the structure chart at a time from the top to the bottom.
A)Top-down approach
B)Bottom-up and top-down approach
C)Bottom-up approach
D)Stepwise refinement

自顶向下的方式是在结构图中从上到下依次实现一个方法。

30)________ is a simple but incomplete version of a method.
A)A stub
B)A main method
C)A method developed using top-down approach
D)A non-main method

待实现的方法可以用存根方法（stub）代替，存根方法是方法的一个简单但不完整的版本。

使用存根方法可以快速地构建程序的框架。