Answers: Java Programmer Certification Mock Exam

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Answers: Java Programmer Certification Mock Exam
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 Double.charValue method.
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 Double.isNaN method returns the result of the expression (v != v).
10	a	Compile-time error at 1	The Float.toString method is overloaded: one declares no parameters and returns the value wrapped by the Float instance; the other accepts a primitive of type float. The literal, 1.0, is of type double and can not be implicitly narrowed to type float.
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 Short.shortValue method and the Short.parseShort method both return primitives of type short. The Short.valueOf method returns an instance of type Short.
14	a	Prints: int primitive	The Integer.parseInt method returns a primitive of type int.
15	g	Run-time error	The Long.parseLong method accepts a String parameter that represents a numeric value. Long.parseLong assumes that the input String represents a decimal value unless a second parameter is provided to specify the radix. All of the characters in the String must be digits of the specified radix. The parseLong method does not determine the type of the numeric value based on a suffix such as l, L, f, F, d, or D. Use of any such suffix generates a NumberFormatException at run-time.
16	e f g	parseDouble toString(double) valueOf
17	i	Compile-time error	The Float.floatValue method is not static; it must be invoked on an instance of type Float.
18	f	Prints: BbB	The Boolean.valueOf method returns a Boolean instance. The Boolean.booleanValue method returns a primitive. The Boolean.TRUE field is a reference to an instance of type Boolean that wraps the primitive value true.

No.

Answer

Remark

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.

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 Double.charValue method.

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.

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.

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.

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.

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.

Prints: long

The Long.parseLong method returns a primitive long.

Prints: true,true,true

NaN is the only value that is not equal to itself. The Double.isNaN method returns the result of the expression (v != v).

Compile-time error at 1

The Float.toString method is overloaded: one declares no parameters and returns the value wrapped by the Float instance; the other accepts a primitive of type float. The literal, 1.0, is of type double and can not be implicitly narrowed to type float.

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.

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.

Prints: p,p,S

The Short.shortValue method and the Short.parseShort method both return primitives of type short. The Short.valueOf method returns an instance of type Short.

Prints: int primitive

The Integer.parseInt method returns a primitive of type int.

Run-time error

The Long.parseLong method accepts a String parameter that represents a numeric value. Long.parseLong assumes that the input String represents a decimal value unless a second parameter is provided to specify the radix. All of the characters in the String must be digits of the specified radix. The parseLong method does not determine the type of the numeric value based on a suffix such as l, L, f, F, d, or D. Use of any such suffix generates a NumberFormatException at run-time.

e f g

parseDouble toString(double) valueOf

Compile-time error

The Float.floatValue method is not static; it must be invoked on an instance of type Float.

Prints: BbB

The Boolean.valueOf method returns a Boolean instance. The Boolean.booleanValue method returns a primitive. The Boolean.TRUE field is a reference to an instance of type Boolean that wraps the primitive value true.

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