Notes

Chapter 10 Object-Oriented Thinking

Section 10.4 Class Relationships
1. ___________ is attached to the class of the composing class to denote the aggregation relationship with the composed object.
a. An empty diamond
b. A solid diamond
c. An empty oval
d. A solid oval
Key:a

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2. An aggregation relationship is usually represented as __________ in ___________.
a. a data field/the aggregating class
b. a data field/the aggregated class
c. a method/the aggregating class
d. a method/the aggregated class
Key:a

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Section 10.7 Processing Primitive Data Type Values as Objects
3. Which of the following statements will convert a string s into i of int type?
a. i = Integer.parseInt(s);
b. i = (new Integer(s)).intValue();
c. i = Integer.valueOf(s).intValue();
d. i = Integer.valueOf(s);
e. i = (int)(Double.parseDouble(s));
Key:abcde All fine. d performs an auto conversion from an Integer object to int.

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4. Which of the following statements will convert a string s into a double value d?
a. d = Double.parseDouble(s);
b. d = (new Double(s)).doubleValue();
c. d = Double.valueOf(s).doubleValue();
d. All of the above.
Key:d All are fine. a is preferred because it does not have to create an object.

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5. Which of the following statements convert a double value d into a string s?
a. s = (new Double(d)).toString();
b. s = d;
c. s = new Double(d).stringOf();
d. s = String.stringOf(d);
e. s = d + "";
Key:ae

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6. Which of the following statements is correct?
a. Integer.parseInt("12", 2);
b. Integer.parseInt(100);
c. Integer.parseInt("100");
d. Integer.parseInt(100, 16);
e. Integer.parseInt("345", 8);
Key:ce (A) is incorrect because 12 is not a binary number. (B) and (D) are incorrect because the first argument in the parseInt method must be a string.

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7. What is the output of Integer.parseInt("10", 2)?
a. 1;
b. 2;
c. 10;
d. Invalid statement;
Key:b Based on 2, 10 is 2 in decimal.

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Section 10.8 Automatic Conversion Between Primitive Types and Wrapper Class Types
8. In JDK 1.5, you may directly assign a primitive data type value to a wrapper object. This is called ______________.
a. auto boxing
b. auto unboxing
c. auto conversion
d. auto casting
Key:a

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9. In JDK 1.5, analyze the following code.

Line 1: Integer[] intArray = {1, 2, 3};
Line 2: int i = intArray[0] + intArray[1];
Line 3: int j = i + intArray[2];
Line 4: double d = intArray[0];
a. It is OK to assign 1, 2, 3 to an array of Integer objects in JDK 1.5.
b. It is OK to automatically convert an Integer object to an int value in Line 2.
c. It is OK to mix an int value with an Integer object in an expression in Line 3.
d. Line 4 is OK. An int value from intArray[0] object is assigned to a double variable d.
Key:abcd

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Section 10.9 The BigInteger and BigDecimal Classes
10. To create an instance of BigInteger for 454, use
a. BigInteger(454);
b. new BigInteger(454);
c. BigInteger("454");
d. new BigInteger("454");
Key:d

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11. To create an instance of BigDecimal for 454.45, use
a. BigInteger(454.45);
b. new BigInteger(454.45);
c. BigInteger("454.45");
d. new BigDecimal("454.45");
Key:d

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12. BigInteger and BigDecimal are immutable
a. true
b. false
Key:a

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13. To add BigInteger b1 to b2, you write _________.
a. b1.add(b2);
b. b2.add(b1);
c. b2 = b1.add(b2);
d. b2 = b2.add(b1);
e. b1 = b2.add(b1);
Key:cd

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14. What is the output of the following code?

public class Test {
public static void main(String[] args) {
java.math.BigInteger x = new java.math.BigInteger("3");
java.math.BigInteger y = new java.math.BigInteger("7");
x.add(y);
System.out.println(x);
}
}
a. 3
b. 4
c. 10
d. 11
Key:a

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15. To divide BigDecimal b1 by b2 and assign the result to b1, you write _________.
a. b1.divide(b2);
b. b2.divide(b1);
c. b1 = b1.divide(b2);
d. b1 = b2.divide(b1);
e. b2 = b2.divide(b1);
Key:c

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16. Which of the following classes are immutable?
a. Integer
b. Double
c. BigInteger
d. BigDecimal
e. String
Key:abcde

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17. Which of the following statements are correct?
a. new java.math.BigInteger("343");
b. new java.math.BigDecimal("343.445");
c. new java.math.BigInteger(343);
d. new java.math.BigDecimal(343.445);
Key:ab

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Section 10.10 The String Class
18. Which of the following statements is preferred to create a string "Welcome to Java"?
a. String s = "Welcome to Java";
b. String s = new String("Welcome to Java");
c. String s; s = "Welcome to Java";
d. String s; s = new String("Welcome to Java");
Key:a (a) is better than (b) because the string created in (a) is interned. Since strings are immutable and are ubiquitous in programming, to improve efficiency and save memory, the JVM uses a unique instance for string literals with the same character sequence. Such an instance is called interned. The JVM (a) is simpler than (c).

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19. What is the output of the following code?

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
Key:a

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20. 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
Key:a Since strings are immutable and are ubiquitous in programming, to improve efficiency and save memory, the JVM uses a unique instance for string literals with the same character sequence. Such an instance is called interned.

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21. 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");
}
}
a. s1 and s2 reference to the same String object
b. s1 and s2 reference to different String objects
Key:b

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22. 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
Key:a

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23. 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 reference to the same String object
b. s1 and s2 have the same contents
c. s1 and s2 have different contents
Key:c

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24. 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
Key:b

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25. Suppose s1 and s2 are two strings. Which of the following statements or expressions are incorrect?
a. String s = new String("new string");
b. String s3 = s1 + s2
c. s1 >= s2
d. int i = s1.length
e. s1.charAt(0) = '5'
Key:cde

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26. What is the output of the following code?

String s = "University";
s.replace("i", "ABC");
System.out.println(s);

a. UnABCversity
b. UnABCversABCty
c. UniversABCty
d. University
Key:d No method in the String class can change the content of the string. String is an immutable class.

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27. Analyze the following code.

class Test {
public static void main(String[] args) {
String s;
System.out.println("s is " + s);
}
}
a. The program has a compile error because s is not initialized, but it is referenced in the println statement.
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 runtime error because s is null in the println statement.
d. The program compiles and runs fine.
Key:a

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28. Which of the following is the correct statement to return a string from an array a of characters?

a. toString(a)
b. new String(a)
c. convertToString(a)
d. String.toString(a)
Key:b

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29. Assume s is " abc ", the method __________ returns a new string "abc".
a. s.trim(s)
b. trim(s)
c. String.trim(s)
d. s.trim()
Key:d

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30. Assume s is "ABCABC", the method __________ returns a new string "aBCaBC".
a. s.toLowerCase(s)
b. s.toLowerCase()
c. s.replace('A', 'a')
d. s.replace('a', 'A')
e. s.replace("ABCABC", "aBCaBC")
Key:ce

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31. Assume s is "ABCABC", the method __________ returns an array of characters.
a. toChars(s)
b. s.toCharArray()
c. String.toChars()
d. String.toCharArray()
e. s.toChars()
Key:b

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32. __________ returns a string.
a. String.valueOf(123)
b. String.valueOf(12.53)
c. String.valueOf(false)
d. String.valueOf(new char[]{'a', 'b', 'c'})
Key:abcd

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33. 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
b. Java and HTML
c. and HTML
d. nothing is displayed
Key:a Inside the method, the statement s = s + " and HTML" creates a new String object s, which is different from the original String object passed to the change(s) method. The original String object has not been changed. Therefore, the output from the original string is Java.

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34. What is displayed by the following statement?
System.out.println("Java is neat".replaceAll("is", "AAA"));
a. JavaAAAneat
b. JavaAAA neat
c. Java AAA neat
d. Java AAAneat
Key:c

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35. What is displayed by the following code?
public static void main(String[] args) {
String[] tokens = "Welcome to Java".split("o");
for (int i = 0; i < tokens.length; i++) {
System.out.print(tokens[i] + " ");
}
}
a. Welcome to Java
b. Welc me to Java
c. Welc me t Java
d. Welcome t Java
Key:c

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36. What is displayed by the following code?
System.out.print("Hi, ABC, good".matches("ABC ") + " ");
System.out.println("Hi, ABC, good".matches(".*ABC.*"));
a. false false
b. true false
c. true true
d. false true
Key:d

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37. What is displayed by the following code?
System.out.print("A,B;C".replaceAll(",;", "#") + " ");
System.out.println("A,B;C".replaceAll("[,;]", "#"));
a. A B C A#B#C
b. A#B#C A#B#C
c. A,B;C A#B#C
d. A B C A B C
Key:c

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38. What is displayed by the following code?

String[] tokens = "A,B;C;D".split("[,;]");
for (int i = 0; i < tokens.length; i++)
System.out.print(tokens[i] + " ");
a. A,B;C;D
b. A B C D
c. A B C;D
d. A B;C;D
Key:b

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Section 10.11 The StringBuilder/StringBuffer Class
39. 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 compile error because you cannot specify initial capacity in the StringBuilder constructor.
b. The program has a runtime error because because the buffer's capacity is 4, but five characters "ABCDE" are appended into the buffer.
c. 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.
d. The program compiles and runs fine.
Key:c The charAt method returns the character at a specific index in the string buffer. The first character of a string buffer is at index 0, the next at index 1, and so on. The index argument must be greater than or equal to 0, and less than the length of the string buffer.

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40. Which of the following is true?
a. You can add characters into a string buffer.
b. You can delete characters into a string buffer.
c. You can reverse the characters in a string buffer.
d. The capacity of a string buffer can be automatically adjusted.
Key:abcd

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41. _________ returns the last character in a StringBuilder variable named strBuf?
a. strBuf.charAt(strBuf.length() - 1)
b. strBuf.charAt(strBuf.capacity() - 1)
c. StringBuilder.charAt(strBuf.length() - 1)
d. StringBuilder.charAt(strBuf.capacity() - 1)
Key:a

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42. Assume StringBuilder strBuf is "ABCDEFG", after invoking _________, strBuf contains "AEFG".
a. strBuf.delete(0, 3)
b. strBuf.delete(1, 3)
c. strBuf.delete(1, 4)
d. strBuf.delete(2, 4)
Key:c

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43. Assume StringBuilder strBuf is "ABCDEFG", after invoking _________, strBuf contains "ABCRRRRDEFG".
a. strBuf.insert(1, "RRRR")
b. strBuf.insert(2, "RRRR")
c. strBuf.insert(3, "RRRR")
d. strBuf.insert(4, "RRRR")
Key:c

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44. Assume StringBuilder strBuf is "ABCCEFC", after invoking _________, strBuf contains "ABTTEFT".
a. strBuf.replace('C', 'T')
b. strBuf.replace("C", "T")
c. strBuf.replace("CC", "TT")
d. strBuf.replace('C', "TT")
e. strBuf.replace(2, 7, "TTEFT")
Key:e

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45. The StringBuilder methods _____________ not only change the contents of a string buffer, but also returns a reference to the string buffer.
a. delete
b. append
c. insert
d. reverse
e. replace
Key:abcde

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46. 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. and HTML
d. nothing is displayed
Key:b Inside the method, the content of the StringBuilder object is changed to Java and HTML. Therefore, the output from buffer is Java and HTML.