Java题库——Chapter2 基础程序设计

1)Suppose a Scanner object is created as follows:

Scanner input = new Scanner(System.in);

What method do you use to read an int value?
A) input.nextInteger(); B) input.integer(); C) input.nextInt(); D) input.int();

2)The following code fragment reads in two numbers: (Choose all that apply.)

Scanner input = new Scanner(System.in);
int i = input.nextInt();
double d = input.nextDouble();

What are the correct ways to enter these two numbers?
A) Enter an integer, a space, a double value, and then the Enter key.
B) Enter an integer, an Enter key, a double value, and then the Enter key.
C) Enter an integer, two spaces, a double value, and then the Enter key.
D) Enter a numeric value with a decimal point, a space, an integer, and then the Enter key.

3)If you enter 1 2 3, when you run this program, what will be the output?

import java.util.Scanner;
public class Test1 {
  public static void main(String[ ] args) {
    Scanner input = new Scanner(System.in);
    System.out.print("Enter three numbers: ");
    double number1 = input.nextDouble();
    double number2 = input.nextDouble();
    double number3 = input.nextDouble();
    // Compute average
    double average = (number1 + number2 + number3) / 3;
    // Display result
    System.out.println(average);
  }
} 

A)1.0 B) 2.0 C) 4.0 D) 3.0

4)Every letter in a Java keyword is in lowercase.
A)true B) false

5)Which of the following is a valid（合法的，有效的） identifier? (Choose all that apply.)
A)$343 B)radius C)9X D)8+9 E)class

6)Which of the following are correct names for variables according to Java naming conventions? (Choose all that apply.)
A)RADIUS B)radius C)FindArea D)Radius E)findArea

• It should start with a lowercase letter such as id, name.
• It should not start with the special characters like & (ampersand), $ (dollar), _ (underscore).
• If the name contains multiple words, start it with the lowercase letter followed by an uppercase letter such as firstName, lastName.
• Avoid using one-character variables such as x, y, z.

7)Which of the following are correct ways to declare variables? (Choose all that apply.)
A)int length; int width; B) int length, int width;
C)int length; width; D) int length, width;

8)________ is the Java assignment operator.
A)== B) = C) := D) =:

9)To assign a value 1 to variable x, you write _______
A)1 = x; B)x = 1; C)1 := x; D)x == 1; E)x := 1;

10)Which of the following assignment statements is incorrect? (Choose all that apply.)
A)i == j == k == 1; B) i = j = k = 1; C)i = 1; j = 1; k = 1; D) i = 1 = j = 1 = k = 1;

11)To declare a constant MAX_LENGTH inside a method with value 99.98, you write ______
A)final float MAX_LENGTH = 99.98; B)double MAX_LENGTH = 99.98;
C)final double MAX_LENGTH = 99.98; D)final MAX_LENGTH = 99.98;

12)Which of the following is a constant, according to Java naming conventions? (Choose all that apply.)
A)MAX_VALUE B)COUNT C)Test D)ReadInt E)read

13)To improve readability and maintainability, you should declare ________ instead of using literal values such as 3.14159.
A)constants B) methods C)classes D) variables

14)Which of these data types requires the most amount of memory?
A)long B) int C) byte D) short

15)To declare an int variable number with initial value 2, you write ______
A)int number = 2; B) int number = 2.0; C)int number = 2L; D) int number = 2l;

16)What is the result of 45 / 4?
A)11 B) 10 C) 11.25 D) 12

17)Which of the following expressions will yield 0.5? (Choose all that apply.)
A)(double) (1 / 2) B)1 / 2 C)1.0 / 2 D)1 / 2.0 E)(double) 1 / 2

18)Which of the following expression results in a value 1?
A)15 % 4 B) 2 % 1 C) 25 % 5 D) 37 % 6

19)25 % 1 is ________.
A)1 B) 2 C) 3 D) 4 E) 0

20)-25 % 5 is ________.
A)1 B) 2 C) 3 D) 4 E) 0

21)24 % 5 is ________.
A)1 B) 2 C) 3 D) 4 E) 0

22)-24 % 5 is ________
A)-1 B) -2 C) -3 D) -4 E) 0

23)-24 % -5 is ________.
A)3 B) -3 C) 4 D) -4 E) 0

24)To add a value 1 to variable x, you write (Choose all that apply.)
A)x = x + 1; B)x := 1; C)1 + x = x; D)x += 1; E)x = 1 + x;

25)To add number to sum, you write (Note: Java is case-sensitive) (Choose all that apply.)

A)number = sum + number; B)sum += number;
C)number += sum; D)sum = sum + number; E)sum = Number + sum;

26)Suppose x is 1. What is x after x += 2?
A)0 B) 1 C) 2 D) 3 E) 4

27)Suppose x is 1. What is x after x -= 1?
A)0 B) 1 C) 2 D) -1 E) -2

28)What is x after the following statements?
int x = 1;
int y = 2;
x *= y + 1;
A)x is 2. B) x is 3. C) x is 4. D) x is 1.

29)What is x after the following statements?
int x = 1;
x *= x + 1;
A)x is 2. B) x is 3. C) x is 1. D) x is 4.

30)Math.pow(2, 3) returns ________.
A) 9.0 B) 9 C) 8.0 D) 8

31)The ________ method returns a raised to the power of b.
A)Math.exponent(a, b) B) Math.pow(b, a) C)Math.pow(a, b) D) Math.power(a, b)

32)Analyze the following code.

public class Test {
  public static void main(String[ ] args) {
    int month = 09;
    System.out.println("month is " + month);
  }  
}

A)The program displays month is 9
B)The program displays month is 9.0
C)The program displays month is 09
D)The program has a syntax error, because 09 is an incorrect literal value.

33)What is y displayed in the following code?

public class Test1 {
  public static void main(String[ ] args) {
    int x = 1;
    int y = x = x + 1;
    System.out.println("y is " + y);
  }  
}

A)y is 1 because x is assigned to y first.
B)y is 2 because x + 1 is assigned to x and then x is assigned to y.
C)y is 0.
D)The program has a compile error since x is redeclared in the statement int y = x = x + 1.

34)What is i printed?

public class Test {
  public static void main(String[ ] args) {
    int j = 0;
    int i = ++j + j * 5;
    System.out.println("What is i? " + i);
  }
}

A)0 B) 1 C) 6 D) 5

35)What is i printed in the following code?

public class Test {
  public static void main(String[ ] args) {
    int j = 0;
    int i = j++ + j * 5;
    System.out.println("What is i? " + i);
  }
}

A)5 B) 6 C) 1 D) 0

36)What is y displayed in the following code?

public class Test {
  public static void main(String[ ] args) {
    int x = 1;
    int y = x++ + x;
    System.out.println("y is " + y);
  }  
}

A)y is 4. B) y is 2. C) y is 3. D) y is 1.

37)What is y displayed?

public class Test {
  public static void main(String[ ] args) {
    int x = 1;
    int y = x + x++;
    System.out.println("y is " + y);
  }  
}

A)y is 1. B) y is 2. C) y is 4. D) y is 3.

38)To assign a double variable d to a float variable x, you write _____
A)x = (float)d; B) x = (int)d; C)x = (long)d D) x = d;

39)What is the printout of the following code:
double x = 5.5;
int y = (int)x;
System.out.println("x is " + x + " and y is " + y);
A)x is 5.5 and y is 5.0
B)x is 6.0 and y is 6.0
C)x is 5.5 and y is 5
D)x is 5 and y is 6
E)x is 6 and y is 6

40)Which of the following assignment statements is illegal? (Choose all that apply.)
A)float f = -34;
B)int t = (int)false;
C)short s = 10;
D)int t = 4.5;
E)int t = 23;

41)What is the value of (double)5/2?
A)2.5 B) 3 C) 3.0 D) 2.0 E) 2

42)What is the value of (double)(5/2)?
A)3 B) 2.0 C) 2.5 D) 2 E) 3.0

 

43)The expression (int)(76.0252175 * 100) / 100 evaluates to ________.
A)76 B) 76.02 C)76.03 D) 76.0252175

44)If you attempt to add an int, a byte, a long, and a double, the result will be a ________ value.

A)int B) byte C) double D) long

45)Which of the following is the correct expression of character 4?
A)'4' B) "4" C) 4 D) '\0004'

46)A Java character is stored in ________.
A)three bytes B) two bytes
C)one byte D) four bytes

JAVA中，char占2字节，16位，可在存放汉字。

47)Suppose x is a char variable with a value 'b'. What is the printout of the statement System.out.println(++x)?
A)b B) d C) c D) a

48)Which of the following statement prints smith\exam1\test.txt?
A)System.out.println("smith\exam1\test.txt");
B)System.out.println("smith\\exam1\\test.txt");
C)System.out.println("smith"\exam1"\test.txt");
D)System.out.println("smith\"exam1\"test.txt");

对\进行转义

49)Suppose i is an int type variable. Which of the following statements display the character whose Unicode is stored in variable i?
A)System.out.println(i); B) System.out.println(i + " ");
C)System.out.println((char)i); D) System.out.println((int)i);

50)The Unicode of 'a' is 97. What is the Unicode for 'c'?
A)96 B) 99 C) 97 D) 98

51)Will System.out.println((char)4) display 4?
A)Yes B) No

52)What is the printout of System.out.println('z' - 'a')?
A)25 B) z C) a D) 26

53)An int variable can hold ________. (Choose all that apply.)
A)120.0 B) 120 C) "120" D) "x" E) 'x'

int型来存放整型和字符类型

54)Which of the following assignment statements is correct? (Choose all that apply.)
A)char c = "100"; B) char c = 'd'; C)char c = 100; D) char c = "d";

55)The expression "Java " + 1 + 2 + 3 evaluates to ________.
A)Java123 B)Java 123 C)java 123 D)Java6 E)Illegal expression

56)Note that the Unicode for character A is 65. The expression "A" + 1 evaluates to ________.

A)B B) A1 C)66 D) Illegal expression

57)Note that the Unicode for character A is 65. The expression 'A' + 1 evaluates to ________.

A)A1 B) 66 C)B D) Illegal expression

int的优先级高于char，向上类型转换

58)The System.currentTimeMillis() returns ________.
A)the current time in milliseconds
B)the current time in milliseconds since midnight, January 1, 1970
C)the current time in milliseconds since midnight, January 1, 1970 GMT (the Unix time)
D)the current time in milliseconds since midnight
E)the current time

59)Programming style is important, because ________. (Choose all that apply.)
A)good programming style can make a program run faster
B)a program may not compile if it has a bad style
C)good programming style helps reduce programming errors
D)good programming style makes a program more readable

60)According to Java naming convention, which of the following names can be variables? (Choose all that apply.)
A)TOTAL_LENGTH B)totalLength C)class D)findArea E)FindArea

61)If a program compiles fine, but it produces incorrect result, then the program suffers ________.
A)a logic error B)a compilation error C)a runtime error

63)The ________ method parses a string s to an int value.
A)integer.parseInt(s); B)Integer.parseInteger(s); C)integer.parseInteger(s); D) Integer.parseInt(s);

64)The ________ method parses a string s to a double value.
A)Double.parsedouble(s); B) double.parse(s);
C)double.parseDouble(s); D) Double.parseDouble(s);

65)Analyze the following code.

import javax.swing.*;
public class ShowErrors {
  public static void main(String[ ] args) {
    int i;
    int j;
    String s = JOptionPane.showInputDialog(null, "Enter an integer", "Input", JOptionPane.QUESTION_MESSAGE);
    j = Integer.parseInt(s);
    i = (i + 4);
  }
} 

A)The program compiles but has a runtime error because i does not have an initial value when it is used in i = i + 4;
B)The program compiles and runs fine.
C)The program cannot compile because i does not have an initial value when it is used in i = i + 4;
D)The program cannot compile because j is not initialized.

 Java未初始化的局部变量不能直接使用