Java题库——Chapter3 操作符、选择

1)The "less than or equal to" comparison operator in Java is ________.
A)<< B) != C) =< D) <= E) <

2)The equal comparison operator in Java is ________.
A)!= B) <> C) ^= D) ==  

3)What is 1 + 1 + 1 + 1 + 1 == 5?
A)true  B)false  C)There is no guarantee that 1 + 1 + 1 + 1 + 1 == 5 is true.

4)What is 1.0 + 1.0 + 1.0 + 1.0 + 1.0 == 5.0?   _______
A)true  B)false  C)There is no guarantee that 1.0 + 1.0 + 1.0 + 1.0 + 1.0 == 5.0 is true.

浮点数不能直接使用==进行比较

5)In Java, the word true is ________.   
A)same as value 0  B) a Boolean literal  C)a Java keyword  D) same as value 1

6)________ is the code with natural language mixed with Java code.   
A)A flowchart diagram  B) Java program  C)A Java statement  D) Pseudocode   

flowchart diagram 流程图

Pseudocode   伪代码

7)Which of the following code displays the area of a circle if the radius is positive?   
A)if (radius <= 0) System.out.println(radius * radius * 3.14159);
B)if (radius > 0) System.out.println(radius * radius * 3.14159);
C)if (radius >= 0) System.out.println(radius * radius * 3.14159);
D)if (radius != 0) System.out.println(radius * radius * 3.14159);

8)Suppose x = 1, y = -1, and z = 1. What is the printout of the following statement?

if (x > 0)
   if (y > 0)
      System.out.println("x > 0 and y > 0");
else if (z > 0)
      System.out.println("x < 0 and z > 0");

A)x > 0 and y > 0; B) x < 0 and z < 0; C)x < 0 and z > 0; D) no printout.

9)Analyze the following code:

boolean even = false;
if (even = true) {
   System.out.println("It is even!");
}

A)The program has a runtime error.
B)The program runs fine, but displays nothing.
C)The program has a compile error.
D)The program runs fine and displays It is even!.

注意这里是赋值=号！！！

10)Analyze the following code.

boolean even = false;
if (even) {
   System.out.println("It is even!");
}   

A)The code is wrong. You should replace if (even) with if (even == true)
B)The code is wrong. You should replace if (even) with if (even = true)
C)The code displays nothing.
D)The code displays It is even!

11)The following code displays ________.

double temperature = 50;
if (temperature >= 100)
   System.out.println("too hot");
else if (temperature <= 40)
   System.out.println("too cold");
else
   System.out.println("just right");

A)too cold  B) just right  C)too hot too cold just right  D) too hot

12)Analyze the following code:
Code 1:

boolean even;
if (number % 2 == 0)
   even = true;
else
   even = false;

Code 2:

boolean even = (number % 2 == 0); 

A)Code 1 has compile errors.
B)Both Code 1 and Code 2 are correct, but Code 2 is better.
C)Both Code 1 and Code 2 have compile errors.
D)Code 2 has compile errors.

13)Suppose income is 4001, what is the output of the following code:

if (income > 3000) {
  System.out.println("Income is greater than 3000");
}
else if (income > 4000) {
  System.out.println("Income is greater than 4000");

A)no output
B)Income is greater than 3000  
C)Income is greater than 4000 followed by Income is greater than 3000
D)Income is greater than 3000 followed by Income is greater than 4000
E)Income is greater than 4000

14)The ________ method immediately terminates the program.
A)System.halt(0); B)System.quit(0); C)System.terminate(0); D)System.stop(0); E)System.exit(0);

15)Which of the Boolean expressions below is incorrect? (Choose all that apply.)
A)(x != 0) || (x = 0)
B)(true) && (3 => 4)
C)(-10 < x < 0)
D)!(x > 0) && (x > 0)
E)(x > 0) || (x < 0)

16)Which of the following is the correct expression that evaluates to true if the number x is between 1 and 100 or the number is negative?
A)((x < 100) && (x > 1)) && (x < 0)
B)1 < x < 100 && x < 0
C)(1 > x >  100) || (x < 0)
D)((x < 100) && (x > 1)) || (x < 0)

17)Suppose x=10 and y=10. What is x after evaluating the expression (y > 10) && (x-- > 10)?  
A)9 B) 11 C) 10

18)Suppose x=10 and y=10 what is x after evaluating the expression (y > 10) && (x++ > 10)?
A)11 B) 10 C) 9

19)Suppose x=10 and y=10 what is x after evaluating the expression (y >= 10) || (x-- > 10)?
A)11 B) 9 C) 10

20)Suppose x=10 and y=10 what is x after evaluating the expression (y >= 10) || (x++ > 10)?
A)10 B) 9 C) 11

21)To check whether a char variable ch is an uppercase letter, you write ________.
A)('A' <= ch <= 'Z') B) (ch >= 'A' || ch <= 'Z')
C)(ch >= 'A' && ch <= 'Z') D) (ch >= 'A' && ch >= 'Z')

22)Analyze the following code:

if (x < 100) && (x > 10)
   System.out.println("x is between 10 and 100");

A)The statement has compile errors because (x<100) & (x > 10) must be enclosed inside parentheses and the println(…) statement must be put inside a block.
B)The statement has compile errors because (x<100) & (x > 10) must be enclosed inside parentheses.
C)The statement compiles fine.
D)The statement compiles fine, but has a runtime error.

23)What is the output of the following code?

char ch = 'F';
if (ch >= 'A' && ch <= 'Z')
   System.out.println(ch); 

A)f B) F C) F f D) nothing

24)What is y after the following switch statement is executed（执行）?

x = 3;
switch (x + 3) {
   case 6:  y = 0;
   case 7:  y = 1;
   default: y += 1;
}

A)4 B) 3 C) 1 D) 2

注意：这里的swich语句中没有break

25)What is the printout of the following switch statement?

char ch = 'a';
switch (ch) {
   case 'a':
   case 'A':
      System.out.print(ch); break;
   case 'b':
   case 'B':
      System.out.print(ch); break;
   case 'c':
   case 'C':
      System.out.print(ch); break;
   case 'd':
   case 'D':
      System.out.print(ch);
} 

A)a B) abc C) abcd D) aa E) ab

26)What is the printout of the following switch statement?

char ch = 'b';
switch (ch) {
   case 'a':
      System.out.print(ch);
   case 'b':
      System.out.print(ch);
   case 'c':
      System.out.print(ch);
   case 'd':
      System.out.print(ch);
} 

A)abcd B) bb C) bcd D) bbb E) b

注意这里case中没有break

27)Analyze the following program fragment:

int x;
double d = 1.5;
switch (d) {
   case 1.0: x = 1;
   case 1.5: x = 2;
   case 2.0: x = 3;
}

A)The program has a compile error because the required default case is missing in the switch statement.
B)The switch control variable cannot be double.
C)The program has a compile error because the required break statement is missing in the switch statement.
D)No errors.

double类型的浮点数只能用一个范围来判断，不能将其具体到一个准确的数字上。

28)What is y after the following statement is executed?

x = 0;
y = (x > 0) ? 10 : -10;

A)0
B)-10
C)10
D)20
E)Illegal expression

29)Analyze the following code fragments that assign a boolean value to the variable even.
Code 1:

if (number % 2 == 0)
   even = true;
else
   even = false;

Code 2:

even = (number % 2 == 0) ? true: false;

Code 3:

even = number % 2 == 0;

A)All three are correct, but Code 1 is preferred.
B)All three are correct, but Code 3 is preferred.
C)All three are correct, but Code 2 is preferred.
D)Code 3 has a compile error, because you attempt to assign number to even.
E)Code 2 has a compile error, because you cannot have true and false literals in the conditional expression.

30)What is the output of the following code?

boolean even = false;
System.out.println((even ? "true" : "false"));

A)false  B) true  C)true false  D) nothing

31)Which of the following are valid specifiers for the printf statement? (Choose all that apply.)
A)%4c  B)%10.2e C)%10b D)%6d E)%8.2d

%c 字符输出  %e 标准科学记数法形式的数  %d 十进制整数输出

32)The statement System.out.printf("%3.1f", 1234.56) outputs ________.
A)1234.6  B)123.5  C)123.4  D)1234.56  E)1234.5

%3.1f 要输出的浮点数至少三位，其中小数部分一位

33)The statement System.out.printf("%3.1e", 1234.56) outputs ________.  
A)0.1e+04  B)0.123456e+04  C)0.123e+04  D)1.23+03  E)1.2e+03

科学计数法的表示，只保留一位整数

34)The statement System.out.printf("%5d", 123456) outputs ________.  
A)12345.6 B) 123456 C) 12345  D) 23456

35)The statement System.out.printf("%10s", 123456) outputs ________. (Note: * represents a space)   
A)23456***** B) 123456****  C)****123456 D) 12345*****

%10s 输出的字符串至少10个字符，如果小于10个字符，就在该字符串前加空格

36)Analyze the following code:
int i = 3434; double d = 3434;
System.out.printf("%5.1f %5.1f", i, d);
A)The code compiles and runs fine to display 3434 3434.0.
B)The code compiles and runs fine to display 3434.0 3434.0.
C)i is an integer, but the format specifier %5.1f specifies a format for double value. The code has an error.

37)The order of the precedence（优先级） (from high to low) of the operators +, *, &&, ||, & is:  ______
A)&, ||, &&, *, +
B)&&, ||, &, *, +
C)*, +, &, ||, &&
D)*, +, &&, ||, &
E)*, +, &, &&, ||

38)Which of the following operators are right-associative（右结合）?   
A)= B) * C) % D) + E) &&

39)What is the value of the following expression?
true || true && false   
A)true B) false

40)Which of the following statements are true? (Choose all that apply.)
A)(x > 0 || x < 10) is same as ((x > 0) || (x < 10))
B)(x > 0 && x < 10) is same as ((x > 0) && (x < 10))
C)(x > 0 || x < 10 && y < 0) is same as (x > 0 || (x < 10 && y < 0))  
D)(x > 0 || x < 10 && y < 0) is same as ((x > 0 || x < 10) && y < 0)

&&条件与的优先级precendence要高于||条件或