Java Programmer Certification Mock Exam

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Answers: Java Programmer Certification Mock Exam
No.	Answer		Remark
1	d	Prints: true,true	An int is a 32-bit signed integral value that is stored in two's complement format. The left most bit is the sign bit. The sign bit is set to one for negative numbers and is set to zero for positive numbers.
2	a b c d e	doubleValue floatValue intValue longValue parseDouble
3	c	Prints: true,false	Long.equals overrides Object.equals. The Long.equals method compares the data values contained in the Long instances. The StringBuffer.equals method does not override Object.equals. The StringBuffer.equals method compares the reference values of the instances. Two distinct instances of StringBuffer will not have the same reference values; so the equals method returns false. The StringBuffer.hashCode method typically returns a value that is based on the internal address of the StringBuffer instance. Two instances of StringBuffer will not have the same hash code.
4	b	Prints: ffF
5	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.
6	c	Compile-time error	The Byte.parseByte method returns a primitive byte. A compile-time error is generated as a result of the attempt to assign a primitive byte to a Byte reference variable.
7	g	Prints: true,true,false	Integer.equals overrides Object.equals. The Integer.equals method compares the data values contained in the Integer instances. If the argument is of type Integer and if the value contained in the argument is the same as the value contained in the instance on which the method is invoked, then the result is true. The equality operator, ==, does not compare data values. Instead, the equality operator compares references. Distinct instances of any two objects can not have the same reference value; so the expression new Integer(i1) == new Integer(i1) is false.
8	g	valueOf
9	b d e	Long.parseLong("1L") Long.parseLong("0x10") Long.parseLong("1.0")	Long.parseLong is overloaded: one version accepts a String argument that represents an integral value; the other accepts both a String argument and an argument of type int. The int argument represents the radix (i.e. base) of the String argument. The Long.parseLong method is not able to determine the type of the String value by examing a suffix such as L. Any such suffix results in a run-time error. The Long.parseLong method is not able to determine the radix of the String value by examing a prefix such as 0 or 0x. The 0 prefix used to identify octal values is accepted, but the String is parsed as a decimal value. The prefix 0x generates a run-time error. The Long.parseLong method generates a run-time error if the String argument is not formatted as a decimal integer. A floating-point format results in a run-time error.
10	e	Prints: true,false,false	Integer.equals overrides Object.equals. The Integer.equals method compares the data values contained in the Integer instances. If the argument is of type Integer and if the value contained in the argument is the same as the value contained in the instance on which the method is invoked, then the result is true. If the argument is not of type Integer then the result is false.
11	e f	parseDouble valueOf
12	b d e	Long.parseLong("+1") Long.parseLong("1L") Long.parseLong("1.0")	Long.parseLong is overloaded: one version accepts a String argument that represents an integral value; the other accepts both a String argument and an argument of type int. The int argument represents the radix (i.e. base) of the decimal integral value represented by the String argument. The Long.parseLong method is not able to determine the type of the String value by examing a suffix such as L. Any such suffix results in a run-time error. The Long.parseLong method is not able to determine the radix of the String value by examing a prefix such as 0 or 0x. The 0 prefix used to identify octal values is accepted, but the String is parsed as a decimal value. The prefix 0x generates a run-time error. A leading minus sign (-) can be added to indicate a negative value. A leading plus sign (+) results in a run-time error. The Long.parseLong method generates a run-time error if the String argument is not formatted as a decimal integer. A floating-point format results in a run-time error.
13	a b	intValue parseInt	Integer.valueOf returns an instance of the Integer wrapper class.
14	e g	parseDouble valueOf
15	c	Prints: true,false	Integer.hashCode overrides Object.hashCode. The Integer.hashCode method calculates the hash code based on the value contained in the Integer instance. The StringBuffer.hashCode method does not override Object.hashCode. The StringBuffer.hashCode method typically returns a value that is based on the internal address of the StringBuffer instance. Two instances of StringBuffer will not have the same hash code.
16	f	Run-time error	An argument of type String must represent a floating-point value. The argument "0x10" represents a hexadecimal integer literal; so a NumberFormatException would be thrown at run-time.
17	b	Prints: false,true	Integer.equals overrides Object.equals. The Integer.equals method compares the data values contained in the Integer instances. The StringBuffer.equals method does not override Object.equals. The StringBuffer.equals method compares the reference values of the instances. Two distinct instances of StringBuffer will not have the same reference values; so the equals method will return false.
18	b d	Compile-time error at 2. Compile-time error at 4.	The Integer.parseInt method is overloaded: one version accepts one argument of type String; the other accepts one String and an int. Both versions of Integer.parseInt return a primitive int. The Integer.intValue method returns the value of the Integer instance as a primitive int. The Integer.valueOf method is overloaded: one version accepts one argument of type String; the other accepts one String and an int. Both versions of Integer.valueOf return an instance of Integer.

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