The pages of this web site are not formatted to conserve paper, but my new book (ISBN: 0-9745862-0-X) is formatted to save paper, save your printer toner, and save money. If you prefer to work my exams from printed pages, then you can save a tree, save your printer toner, and save money if you buy my new book instead of attempting to print the pages of my web site.
Today, you can find my book on the retail web site of the company that prints it and distributes it.
| No. | Answer | Remark | |
|---|---|---|---|
| 1 | d | Compile-time error | Long is a subclass of the abstract class Number, and Long implements all of the methods of Number: byteValue, shortValue, intValue, longValue, floatValue and doubleValue. The attempt to invoke the charValue method on an instance of Long generates a compile-time error, because there is no charValue method. |
| 2 | d | Prints: -1,-1,true |
Double
is a subclass of the abstract class
Number,
and implements all of the methods of
Number
such as
byteValue,
shortValue,
floatValue,
etc.
In this case, the
Double
instance contains the value
0xFFFF.
When that value is converted to type
byte
the result is
0xFF
which is also the two's complement representation of the
byte
value -1. Similarly,
0xFFFF
is the two's complement representation of the
short
value -1.
Please note there is no
|
| 3 | b d f | new Float("A") new Float("1L") new Float("0x10") | The Float constructor is overloaded: one version accepts a primitive of type float; one accepts a primitive of type double; one accepts a String representation of a floating-point literal. The primitive char literal 'A' is converted to a float, and is accepted by the constructor that declares a parameter of type float. The String literals "NaN" and "Infinity" are accepted by the Float constructor. A sign (+ or -) is optional. The API specification states that any other String must represent a floating-point value; however, a little experimentation proves that a String is acceptable if it can be parsed as a decimal integer value. The leading 0 of an octal value is ignored, and the String is parsed as a decimal value. A String representation of a hexadecimal value is not acceptable. The String "A" does not represent a floating-point literal value; therefore, a NumberFormatException is thrown. Arguments of type String can not contain an integer type suffix, L or l. A floating-point suffix, F, f, D or d, is acceptable, but the suffix has no impact on the result. |
| 4 | e | Prints: true,false,false | The Boolean constructor is overloaded: one version accepts a primitive boolean argument; the other accepts a String. If the String value is the word true, then the new Boolean instance will contain the value true. Both upper and lower case letters are acceptable. If the String contains any word other than true or if the reference is null, then the new instance will contain the value false. |
| 5 | b | Prints: false,true | The expression b1==b2 compares the references of two instances of Byte. The result is false, because the instances are distinct. The expression b1.equals(b2) compares the contents of two instances of Byte. The result is true, because the two instances contain the same value. |
| 6 | d | false,true,true | The equality expression s1==s2 compares the reference values of two distinct instances of type Short. Since the instance are distinct, the equality expression is false. The expression s1.equals(s2) compares the values of two instances of type Short. Since both instances contain the value 1, the returned value is true. The expression a1==b1 compares the hash codes of two instances of Short. The result is true, because the two instances contain the same value. |
| 7 | k | None of the above | The binary representation of 256 is one bit that is set to one followed by eight bits that are set to zero. When 256 is converted to an eight bit byte value, the bit that is set to one is lost and only the bits that are set to zero remain. When 256 is converted to a short, no information is lost; so the value remains 256. |
| 8 | a | Prints: long | The Long.parseLong method returns a primitive long. |
| 9 | h | Prints: true,true,true |
NaN
is the only value that is not equal to itself. The
|
| 10 | a | Compile-time error at 1 |
The
|
| 11 | c | Prints: false,true,false | The Boolean.valueOf method is overloaded: one version accepts a primitive boolean argument; the other accepts a String. If the String value is the word true, then the new Boolean instance will contain the value true. Both upper and lower case letters are acceptable. If the String contains any word other than true or if the String reference is null, then the new instance will contain the value false. |
| 12 | d | Prints: true,true | The expression b1.equals(b2) compares the values of two instances of type Byte. Since both instances contain the value 1, the return value is true. The expression a==b compares the hash codes of two instances of Byte. The result is true, because the two instances contain the same value. |
| 13 | b | Prints: p,p,S |
The
|
| 14 | a | Prints: int primitive |
The
|
| 15 | g | Run-time error |
The
|
| 16 | e f g | parseDouble toString(double) valueOf | |
| 17 | i | Compile-time error |
The
|
| 18 | f | Prints: BbB |
The
|