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
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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
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67. Composition means .
a. that data fields should be declared private
a. that data fields should be declared private
b. that a class extends another class
c. that a variable of supertype refers to a subtype object
d. that a class contains a data field that references another object
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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));
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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.
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6. Which of the following statements are 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;
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5. Which of the following statements convert a double value d into a string s?
a. s = Double.valueOf(d).toString();
b. s = d;
c. s = Double.valueOf(d).stringOf();
d. s = String.stringOf(d);
e. s = d + “”;
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Section 10.8 Automatic Conversion Between Primitive Types and Wrapper Class Types
8. 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
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9. 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.
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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”);
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13. To add BigInteger b1 to b2, you write .
a.
3
b.
4
c.
10
d.
11
a. b1.add(b2);
b. b2.add(b1);
c. b2 = b1.add(b2);
d. b2 = b2.add(b1);
e. b1 = b2.add(b1);
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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);
}
}
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11. To create an instance of BigDecimal for 454.45, use
a. BigDecimal(454.45);
b. new BigDecimal(454.45);
c. BigDecimal(“454.45”);
d. new BigDecimal(“454.45”);
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12. BigInteger and BigDecimal are immutable.
a. true
b. false
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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, 20, RoundingMode.HALF_UP);
d. b1 = b2.divide(b1, 20, RoundingMode.HALF_UP);
e. b2 = b2.divide(b1, 20, RoundingMode.HALF_UP);
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16. Which of the following classes are immutable?
a. Integer
b. Double
c. BigInteger
d. BigDecimal
e. String
Key:abcde All the number classes and the String class are immutable.
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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);
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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”);
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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.
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Section 10.10.1 Immutable Strings and Interned Strings
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
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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
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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
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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
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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 are of different objects”);
}
}
a. s1 and s2 reference to the same String object
b. s1 and s2 have the same contents
c. s1 and s2 are of different objects
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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
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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’
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Section 10.10.2 Replacing and Splitting Strings
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
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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”)
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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
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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 “is” replaced by “AAA” in “Java is neat”. So “Java is neat”.replaceAll(“is”, “AAA”) returns “Java AAA neat”.
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Section 10.10.3 Matching, Replacing, and Splitting by Patterns
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
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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
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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
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Section 10.10.4 Conversion between Strings and Arrays
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)
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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 The trim() method trims the whitespace characters from both the left and right sides of the string.
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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()
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Section 10.10.5 Converting Characters and Numeric Values
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’})
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Section 10.11 The StringBuilder/StringBuffer Class
33. The following program displays .
public class Test {
public static void main(String[] args) {
String s = “Java”;
StringBuilder builder = 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
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Section 10.11.1 Modifying Strings in the StringBuilder
39. Analyze the following code.
class Test {
public static void main(String[] args) {
StringBuilder strBuilder = new StringBuilder(4);
strBuilder.append(“ABCDE”);
System.out.println(“What’s strBuilder.charAt(5)? ”
+ strBuilder.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 builder’s capacity is 4, but five characters “ABCDE” are
appended into the builder.
c. The program has a runtime error because the length of the string in the builder is 5 after “ABCDE” is appended into
the builder. Therefore, strBuilder.charAt(5) is out of range.
d. The program compiles and runs fine.
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46. The following program displays .
public class Test {
public static void main(String[] args) {
String s = “Java”;
StringBuilder builder = new StringBuilder(s);
change(builder);
System.out.println(builder);
}
private static void change(StringBuilder builder) {
builder.append(” and HTML”);
}
}
a. Java
b. Java and HTML
c. and HTML
d. nothing is displayed
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40. Which of the following is true?
a. You can add characters into a string builder.
b. You can delete characters from a string builder.
c. You can reverse the characters in a string buffer.
d. The capacity of a string buffer can be automatically adjusted.
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42. Assume StringBuilder strBuilder is “ABCDEFG”, after invoking , strBuilder contains “AEFG”.
a. strBuilder.delete(0, 3)
b. strBuilder.delete(1, 3)
c. strBuilder.delete(1, 4)
d. strBuilder.delete(2, 4)
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43. Assume StringBuilder strBuilder is “ABCDEFG”, after invoking , strBuilder contains
“ABCRRRRDEFG”.
a. strBuilder.insert(1, “RRRR”)
b. strBuilder.insert(2, “RRRR”)
c. strBuilder.insert(3, “RRRR”)
d. strBuilder.insert(4, “RRRR”)
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44. Assume StringBuilder strBuilder is “ABCCEFC”, after invoking , strBuilder contains “ABTTEFT”.
a. strBuilder.replace(‘C’, ‘T’)
b. strBuilder.replace(“C”, “T”)
c. strBuilder.replace(“CC”, “TT”)
d. strBuilder.replace(‘C’, “TT”)
e. strBuilder.replace(2, 7, “TTEFT”)
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45. The StringBuilder methods not only change the contents of a string builder, but also returns a
reference to the string builder.
a. delete
b. append
c. insert
d. reverse
e. replace
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Section 10.11.2 The toString, capacity, length, setLength, and charAt Methods
41. returns the last character in a StringBuilder variable named strBuilder?
a. strBuilder.charAt(strBuilder.length() – 1)
b. strBuilder.charAt(strBuilder.capacity() – 1)
c. StringBuilder.charAt(strBuilder.length() – 1)
d. StringBuilder.charAt(strBuilder.capacity() – 1)