1)Which code fragment would correctly identify the number of arguments passed via the command line to a Java application, excluding the name of the class that is being invoked?
Which code fragments can correctly identify the number of passes through the command-line parameters to Java applications without including the name of the calling class?
A)int count=0; while (!(args[count].equals(""))) count ++;
B)int count = args.length - 1;
C)int count = args.length;
D)int count = 0; while (args[count] != null) count ++;
2)Which class do you use to write data into a text file? 2) _______
A)File B) System C)Scanner D) PrintWriter
3)Analyze the following code.
class Test { public static void main(String[ ] args) { String s; System.out.println("s is " + s); } }
A)The program compiles and runs fine.
B)The program has a runtime error because s is not initialized, but it is referenced in the println statement.
C)The program has a compilation error because s is not initialized, but it is referenced in the println statement.
D)The program has a runtime error because s is null in the println statement.
4)How can you get the word "abc" in the main method from the following call?
java Test "+" 3 "abc" 2 4) _______
A)args[2] B) args[1] C) args[3] D) args[0]
5)What is the output of the following code?
public class Test { public static void main(String[ ] args) { String s1 = new String("Welcome to Java!"); String s2 = new String("Welcome to Java!"); if (s1.equals(s2)) System.out.println("s1 and s2 have the same contents"); else System.out.println("s1 and s2 have different contents"); } }
A)s1 and s2 have the same contents
B)s1 and s2 have different contents
s.equals () method is to determine whether the contents of the string are equal, returns true as long as the content is equal to
6)What is the output of the following code?
public class Test {
public static void main(String[ ] args) {
String s1 = "Welcome to Java!";
String s2 = "Welcome to Java!";
if (s1 == s2)
System.out.println("s1 and s2 reference to the same String object");
else
System.out.println("s1 and s2 reference to different String objects");
}
}
A)s1 and s2 reference to the same String object
B)s1 and s2 reference to different String objects
"==" method of determining an address is the same whether the two strings, i.e., if a, b two strings, they point to the same object, i.e., the same address, with the "==" returns true
7)Which of the following is true? (Choose all that apply.) 7) _______
A)You can add characters into a string buffer.
B)The capacity of a string buffer can be automatically adjusted.
C)You can reverse the characters in a string buffer.
D)You can delete characters into a string buffer.
The String class is a string constant, a constant can not be changed. The StringBuffer is a string variable, it is an object can be expanded and modified.
. 8) Check the To the contains S IF A String The suffix "the Java", you On May Write (the Choose All that Apply).
A) IF (s.charAt (s.length () -. 4) == 'J' && s.charAt (s.length () - 3) == 'a' && s.charAt (s.length () - 2) == 'v' && s.charAt (s.length () - 1) == 'a' ) ...
B) IF (s.substring (s.length () -. 5) .equals ( "the Java")) ... S may only contain "the Java"
C) IF (s.lastIndexOf ( "the Java" )> = 0) ... lastIndexOf return value must be greater than 0! I can not find returns -1 does not exist!
D) IF (s.endsWith ( "the Java")) ...
E) IF (s.substring (s.length () - 4) .equals ( "the Java")) ...
9)What is displayed by the following code?
public static void main(String[ ] args) throws Exception { String[ ] tokens = "Welcome to Java".split("o"); for (int i = 0; i < tokens.length; i++) { System.out.print(tokens[i] + " "); } }
A)Welc me to Java
B) Welcome to Java
C)Welcome t Java
D) Welc me t Java
split function is specified for the character (string) or to split a regular string, returns the result in the form of an array of strings
10)Which class do you use to read data into a text file? 10) ______
A)Scanner B) System C)PrintWriter D) File
11)Suppose you enter 34.3 57.8 789, then press the ENTER key. Analyze the following code.
Scanner scanner = new Scanner(System.in); int value = scanner.nextDouble(); int doubleValue = scanner.nextInt(); String line = scanner.nextLine();
A)After the last statement is executed, intValue is 34. 注意这里没有进行强制类型转换！
B)After the last statement is executed, line contains characters '7', '8', '9', '\n'.
C)After the last statement is executed, line contains characters '7', '8', '9'.
D)The program has a runtime error because 34.3 is not an integer.
12)Which of the following statements are true? 12) ______
A)If a file (e.g., c:\temp.txt) does not exist, new File("c:\\temp.txt") creates a new file named c:\temp.txt.
B)If a directory (e.g., c:\liang) does not exist, new File("c:\liang") creates a new directory named c:\liang.
C)If a file (e.g., c:\temp.txt) does not exist, new File("c:\\temp.txt") returns null.
D)If a directory (e.g., c:\liang) does not exist, new File("c:\liang") returns null.
E)None of the above.
13)Which of following is not a correct method in Character? (Choose all that apply.) 13) ______
A)isLetter(char) B)isDigit() C)isLetterOrDigit(char) D)toLowerCase(char) E)toUpperCase()
B, E needed parameters
14)Which class contains the method for checking whether a file exists? 14) ______
A)System B) Scanner C)File D) PrintWriter
15)Which of the following statements creates an instance of File on Window for the file c:\t.txt?
A)new File("c:\txt.txt") B) new File("c:\\txt.txt")
C)new File("c://txt.txt") D) new File("c:/txt.txt")
16)________ returns the last character in a StringBuilder variable named strBuf? 16) ______
A)StringBuilder.charAt(strBuf.capacity() - 1)
B)strBuf.charAt(strBuf.capacity() - 1)
C)StringBuilder.charAt(strBuf.length() - 1)
D)strBuf.charAt(strBuf.length() - 1)
17)Assume StringBuilder strBuf is "ABCCEFC", after invoking ________, strBuf contains "ABTTEFT". 17) ______
A)strBuf.replace("C", "T")
B)strBuf.replace("CC", "TT")
C)strBuf.replace('C', 'T')
D)strBuf.replace('C', "TT")
E)strBuf.replace(2, 7, "TTEFT")
18)Which of the following returns the path separator character? 18) ______
A)File.separatorChar
B)File.pathSeparatorChar
C)File.pathSeparator
D)File.separator
E)None of the above.
19)Analyze the following code.
class Test { public static void main(String[ ] args) { StringBuilder strBuf = new StringBuilder(4); strBuf.append("ABCDE"); System.out.println("What's strBuf.charAt(5)? " + strBuf.charAt(5)); } }
A)The program has a runtime error because the length of the string in the buffer is 5 after "ABCDE" is appended into the buffer. Therefore, strBuf.charAt(5) is out of range.
B)The program compiles and runs fine.
C)The program has a runtime error because because the buffer's capacity is 4, but five characters "ABCDE" are appended into the buffer.
D)The program has a compilation error because you cannot specify initial capacity in the StringBuilder constructor.
20)Suppose Character x = new Character('a'), ________ returns true. (Choose all that apply.)
A)x.equals(new Character('a'))
B)x.compareToIgnoreCase('A')
C)x.equals('a')
D)x.equals("a")
E)x.equalsIgnoreCase('A')
21)The following program displays ________.
public class Test { public static void main(String[ ] args) { String s = "Java"; StringBuilder buffer = new StringBuilder(s); change(s); System.out.println(s); } private static void change(String s) { s = s + " and HTML"; } }
A)Java and HTML B) and HTML C)nothing is displayed D) Java
StringBuilder is mutable class, String is immutable class! !
22)To check if a string s contains the prefix "Java", you may write (Choose all that apply.)
A)if (s.indexOf("Java") == 0) ...
B)if (s.startsWith("Java")) ...
C)if (s.substring(0, 4).equals("Java")) ...
D)if (s.charAt(0) == 'J' && s.charAt(1) == 'a' && s.charAt(2) == 'v' && s.charAt(3) == 'a') ...
23)Which of the following statements is preferred to create a string "Welcome to Java"?
A)String s; s = new String("Welcome to Java");
B)String s = "Welcome to Java";
C)String s; s = "Welcome to Java";
D)String s = new String("Welcome to Java");
Note that the subject demands, more suitable! In fact, D is correct, but there is no B is more suitable!
24)Which method can be used to write data? 24) ______
A)exist B) print C) close D) rename
25)Which method can be used to create an output object for file temp.txt? (Choose all that apply.)
A)new PrintWriter("temp.txt")
B)new PrintWriter(new File("temp.txt"))
C)new PrintWriter(File("temp.txt"))
D)new PrintWriter(temp.txt)
26)Assume StringBuilder strBuf is "ABCDEFG", after invoking ________, strBuf contains "AEFG". 26) ______
A)strBuf.delete(1, 3) B) strBuf.delete(2, 4) C)strBuf.delete(0, 3) D) strBuf.delete(1, 4)
Starting from the character to the specified position beginIndex endIndex-1 subscript characters, note character at endIndex position not part of the string!
27)Suppose you enter 34.3, the ENTER key, 57.8, the ENTER key, 789, the ENTER key. Analyze the following code.
Scanner scanner = new Scanner(System.in); int value = scanner.nextDouble(); int doubleValue = scanner.nextInt(); String line = scanner.nextLine();
A)After the last statement is executed, intValue is 34.
B)After the last statement is executed, line contains characters '7 ', '8 ', '9'.
C)After the last statement is executed, line contains character '\n '.
D)The program has a runtime error because 34.3 is not an integer.
E)After the last statement is executed, line contains characters '7', '8', '9', '\n'.
28)Which of the following is the correct statement to return a string from an array a of characters?
A)toString(a) B) convertToString(a) C)new String(a) D) String.toString(a)
29)What is the return value of "SELECT".substring(0, 5)? 29) ______
A)"SELECT" B) "SELE" C)"SELEC" D) "ELECT"
Starting from the character to the specified position beginIndex endIndex-1 subscript characters, note character at endIndex position not part of the string!
30)Suppose s1 and s2 are two strings. What is the result of the following code?
s1.equals(s2) == s2.equals(s1)
A)true B) false
31)Which method can be used to create an input object for file temp.txt? 31) ______
A)new Scanner("temp.txt")
B)new Scanner(temp.txt)
C)new Scanner(File("temp.txt"))
D)new Scanner(new File("temp.txt"))
32)Assume s is "ABCABC", the method ________ returns an array of characters. 32) ______
A)String.toCharArray()
B)String.toChars()
C)s.toCharArray()
D)s.toChars()
E)toChars(s)
33)Which correctly creates an array of five empty Strings? 33) ______
A)String[ ] a = new String [5];
B)String[ ] a = {"", "", "", "", ""};
C)String[ ] a = new String [5]; for (int i = 0; i < 5; a[i++] = null);
D)String[5] a;
34)Assume StringBuilder strBuf is "ABCDEFG", after invoking ________, strBuf contains "ABCRRRRDEFG". 34) ______
A)strBuf.insert(1, "RRRR") B) strBuf.insert(3, "RRRR")
C)strBuf.insert(2, "RRRR") D) strBuf.insert(4, "RRRR")
35)Suppose s1 and s2 are two strings. Which of the following statements or expressions are incorrect? (Choose all that apply.) 35) ______
A)s1.charAt(0) = '5'
B)String s = new String("new string");
C)String s3 = s1 + s2
D)s1 >= s2
E)int i = s1.length
E to be written in int i = s1.length ()
36)Suppose s1 and s2 are two strings. Which of the following statements or expressions is incorrect? (Choose all that apply.) 36) ______
A)char c = s1.charAt(s1.length()); 数组越界
B)boolean b = s1.compareTo(s2); 必为flase
C)char c = s1[0];
D)String s3 = s1 - s2;
37)What are the reasons to create an instance of the File class? (Choose all that apply.) 37) ______
A)To delete the file.
B)To read/write data from/to a file
C)To rename the file.
D)To obtain the properties of the file such as whether the file can be read, written, or is hidden.
E)To determine whether the file exists.
38)Identify the problems in the following code.
public class Test { public static void main(String argv[ ]) { System.out.println("argv.length is " + argv.length); } }
A)The program has a compile error because String argv[ ] is wrong and it should be replaced by String[ ] args.
B)If you run this program without passing any arguments, the program would display argv.length is 0.
C)If you run this program without passing any arguments, the program would have a runtime error because argv is null.
D)The program has a compile error because String args[ ] is wrong and it should be replaced by String args[ ].
39)What is the return value of "SELECT".substring(4, 4)? 39) ______
A)T B) an empty string C)C D) E
40)Assume s is " abc ", the method ________ returns a new string "abc". 40) ______
A)trim(s) B) String.trim(s) C)s.trim(s) D) s.trim()
Effect trim () is to remove extra spaces at both ends of the string, it is noted that both ends of the space, and whether the number of spaces at both ends will be removed, of course, those of the intermediate space are not removed
41)"abc".compareTo("aba") returns ________. 41) ______
A)1 B) 0 C) -1 D) -2 E) 2
From the first start comparing two strings, if you encounter different characters, then immediately returns ascii value of the difference between these two characters. The return value is an int
42)What is the output of the following code?
public class Test { public static void main(String[ ] args) { String s1 = new String("Welcome to Java"); String s2 = s1; s1 += "and Welcome to HTML"; if (s1 == s2) System.out.println("s1 and s2 reference to the same String object"); else System.out.println("s1 and s2 reference to different String objects"); } }
A)s1 and s2 reference to the same String object
B)s1 and s2 reference to different String objects
43)Which method can be used to read a whole line from the file? 43) ______
A)nextDouble B) nextLine C)next D) nextInt
44)Which of the following is the correct header of the main method? (Choose all that apply.)
A)static void main(String[ ] args)
B)public static void main(String args[ ])
C)public static void main(String x[ ])
D)public static void main(String[ ] x)
E)public static void main(String[ ] args)
45)What is displayed by the following statement?
System.out.println("Java is neat".replaceAll("is", "AAA")); 45) ______
A)JavaAAA neat B) Java AAAneat C)Java AAA neat D) JavaAAAneat
46)"AbA".compareToIgnoreCase("abC") returns ________. 46) ______
A)2 B) -1 C) -2 D) 0 E) 1
compareToIgnoreCase insensitive comparison from the first start comparing two strings, if you encounter different characters, then immediately returns ascii value of the difference between these two characters. The return value is an int
47)The StringBuilder methods ________ not only change the contents of a string buffer, but also returns a reference to the string buffer. (Choose all that apply.) 47) ______
A)insert B)replace C)delete D)append E)reverse
48)________ returns true. (Choose all that apply.) 48) ______
A)"peter".equalsIgnoreCase("Peter")
B)"peter".compareToIgnoreCase("peter")
C)"peter".compareToIgnoreCase("Peter")
D)"peter".equals("peter")
E)"peter".equalsIgnoreCase("peter")
equalsIgnoreCase case-insensitive comparison
49)The following program displays ________.
public class Test { public static void main(String[ ] args) { String s = "Java"; StringBuilder buffer = new StringBuilder(s); change(buffer); System.out.println(buffer); } private static void change(StringBuilder buffer) { buffer.append(" and HTML"); } }
A)Java B) Java and HTML C)nothing is displayed D) and HTML
StringBuilder is mutable class! !
50)Suppose s is a string with the value "java". What will be assigned to x if you execute the following code?
char x = s.charAt(4);
A)'a' B)'v'
C)Nothing will be assigned to x, because the execution causes the runtime error StringIndexOutofBoundsException.
51)What is the output of the following code?
public class Test { public static void main(String[ ] args) { String s1 = new String("Welcome to Java!"); String s2 = new String("Welcome to Java!"); if (s1 == s2) System.out.println("s1 and s2 reference to the same String object"); else System.out.println("s1 and s2 reference to different String objects"); } }
Here s1 and s2 are new new out, pointing to the two objects!
A) Different S1 and S2 to Reference String Objects B) S1 and S2 to Reference String Object The Same
52)________ returns a string. (Choose all that apply.) 52) ______
A)String.valueOf(new char[ ]{'a', 'b', 'c'})
B)String.valueOf(123)
C)String.valueOf(12.53)
D)String.valueOf(false)
53)Suppose you enter 34.3 57.8 789, then press the ENTER key. Analyze the following code.
Scanner scanner = new Scanner(System.in); int intValue = scanner.nextInt(); int doubleValue = scanner.nextInt(); String line = scanner.nextLine();
A)After the last statement is executed, line contains characters '7', '8', '9', '\n'.
B)After the last statement is executed, intValue is 34.
C)After the last statement is executed, line contains characters '7', '8', '9'.
D)The program has a runtime error because 34.3 is not an integer.
54)Given the following program:
public class Test { public static void main(String[ ] args) { for (int i = 0; i < args.length; i++) { System.out.print(args[i] + " "); } } }
What is the output, if you run the program using
java Test 1 2 3
A)3 B) 1 2 C) 1 D) 1 2 3
The program has three parameters!
55) What is the output of the
public class Test { public static void main(String[ ] args) { String s1 = "Welcome to Java!"; String s2 = s1; if (s1 == s2) System.out.println("s1 and s2 reference to the same String object"); else System.out.println("s1 and s2 reference to different String objects"); } }
A)s1 and s2 reference to the same String object B)s1 and s2 reference to different String objects
56)Which of the following is the correct statement to return JAVA? 56) ______
A)"Java".toUpperCase() B) "Java".toUpperCase("Java")
C)toUpperCase("Java") D) String.toUpperCase("Java")
57)What is the output of the following code?
String s = "University";
s.replace("i", "ABC");
System.out.println(s);
A)University B) UnABCversABCty C)UnABCversity D) UniversABCty
s.replace ( "i", "ABC"); the object does not return!
58)Assume s is "ABCABC", the method ________ returns a new string "aBCaBC". 58) ______
A)s.replace("ABCABC", "aBCaBC")
B)s.toLowerCase()
C)s.replace('A', 'a')
D)s.toLowerCase(s)
E)s.replace('a', 'A')
59)What is the output of the following code?
public class Test {
public static void main(String[ ] args) {
String s1 = new String("Welcome to Java!");
String s2 = s1.toUpperCase();
if (s1 == s2)
System.out.println("s1 and s2 reference to the same String object");
else if (s1.equals(s2))
System.out.println("s1 and s2 have the same contents");
else
System.out.println("s1 and s2 have different contents");
}
}
A)s1 and s2 have the same contents
B)s1 and s2 reference to the same String object
C)s1 and s2 have different contents