Answers: Java Programmer Certification Mock Exam

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Answers: Java Programmer Certification Mock Exam
No.	Answer	Remark
1	b	Prints: null	The System.out.print method prints the word null if the argument is a String reference that is null.
2	a b	abstract public	The modifier, abstract, is applicable to an interface declaration, but its use is strongly discouraged; because every interface is implicitly abstract. If an interface is declare public, then the compiler will generate an error if the class is not stored in a file that has the same name as the interface plus the extension .java. The modifier, static, is applicable to a member interface, but not to an interface that is not nested. The modifier, synchronized, is applicable only to concrete implementations of methods. The modifiers, transient and volatile, are applicable only to variables.
3	b d f	0x0000 to 0xffff 0 to 0177777 0 to 65535	A char is a 16 bit unsigned value; so none of the char values are negative and the minimum value is zero. The maximum value is 2¹⁶ - 1.
4	d	Prints: true,true	The sign of an integral numeric type is changed by inverting all of the bits and by adding one.
5	c d	3 4	This question demonstrates a variety of assignment conversions. The compiler will implicitly do a narrowing conversion for an assignment statement if the right hand operand is a compile time constant of type byte, short, char, or int and the value falls within the range of the variable on the left and if the variable on the left is of type byte, short, or char. In this case, variables s1 and c1 are not compile time constants so the compiler will not do an implicit narrowing conversion. However, variables s2 and c2 are compile time constants that fall within the range of the left hand operand. For more information, please see JLS section 5.2.
6	c	The internal data model can be read and modified only through accessor and mutator methods.	A class is not tightly encapsulated if the internal data model can be read and/or modified without working through accessor (i.e. get) and mutator (i.e. set) methods.
7	d	InterruptedException	The methods Object.wait, Thread.join and Thread.sleep name InterruptedException in their throws clauses.
8	b	Prints: A B C	The String instance referenced by s2 is passed to the m1 method by passing the value of the reference. The reference value used in method m1 is a local copy of the reference. If the local copy used in method m1 is changed, then the original reference variable in the main method remains unchanged.
9	b	Compile-time error at 1	At line 1, the invocation of the Math.min method produces a return value of type int. The variable b1 is of type short; so the assignment expression results in a compile-time error. The Math class declares four versions of the min method; each declares a pair of parameters of the same type. The parameter pair can be of type int, long, float or double. The return type is the same as the argument types. At run-time, the arguments might not match the declared parameter types; so one argument or both might require an implicit conversion to an acceptable type. If both arguments are of type byte, short or char, then both will be promoted to type int. If only one argument is of type byte, short or char, then it will be promoted to the type of the other argument. If both arguments are of type int, long, float or double but the types differ, then a primitive widening conversion will be applied to one of the two arguments.
10	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.
11	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.
12	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.
13	g	valueOf
14	c	TreeSet	The elements are not key/value pairs; so a Map is not a good choice. A List generally accepts duplicate elements. A Set stores a collection of unique objects; so any attempt to store a duplicate object is rejected. TreeSet stores elements in an order that is determined either by a Comparator or by the Comparable interface.
15	d	Prints: false,true,true	HashSet implements the Set interface, but not the Map interface. HashMap extends AbstractMap and implements the Map interface. Hashtable extends Dictionary and implements the Map interface.
16	a b	return 31; return getI1();	A hashCode method that returns the constant value 31 is consistent with the hash code contract. Even so, a hashCode method that returns the same value regardless of the internal state of the object is not very good, because it will cause hashtables to place every instance of the class in the same bucket. If the equals method determines that two instances are equal, then the two instances must produce the same hash code. For that reason, the hash code must not be calculated using fields that are not used to determine equality. In this case, the equals method determines equality based on the value of i1. The value of i2 is not used to determine equality; therefore, i2 can not be used to calculate the hash code.
17	e	5	The synchronized modifier is a method modifier and can not be applied to a field.
18	c d e	3 4 5	The abstract and final modifiers can be applied to a method local class declaration.
19	c	Prints: C	The boolean type variable, b, is initialized to true. The boolean expression of the first if statement, b = false, is a simple assignment expression that sets b to false. Always look carefully at the boolean expression of an if statement to verify that the expected equality operator (==) has not been replaced by the simple assignment operator (=).
20	f	Compile-time error at line 4.	Anytime a field is accessed from within a static context it is very important to verify that the field is also static. If the field is instead an instance variable then the result is a Compile-time error.
21	d	Prints: GFC206,GFC206	Type GFC207 is a subclass of types GFC206 and GFC205, so any of the four methods are applicable to the method invocation expression, m(gfc207, gfc207). The most specific of the four, m(GFC206 x, GFC206 y), is chosen. Type GFC206 is a subclass of type GFC205, and method m(GFC206 x, GFC206 y) is more specific than the other three, because any invocation of m(GFC206 x, GFC206 y) could also be handled by any of the other three without causing a compile-time type error.
22	a	Prints: ABCI	Suppose that a class extends a superclass, X, or implements an interface, X. The field access expression ((X)this).hiddenField is used to access the hidden field, hiddenField, that is accessible within the superclass or interface, X.
23	d	G.this.s1	The qualified this expression ClassName.this.name can be used to access shadowed variables declared within an enclosing class.
24	d	Compile-time error	The declarations of b1 and c1 cause compile-time errors, because a reference of a subclass type can not refer to an instance of the superclass type.
25	c e	3 5	Local method variables and method parameters are stored on the stack and go out of scope after the method is exited. Although a local reference variable is stored on the stack, the referenced object is stored on the heap; so the object can continue to exist long after the method runs to completion. An object that is instantiated within a method or block is not permitted to refer to a variable that is declared within the method or block unless the variable is declared final and the variable declaration precedes the creation of the object.
26	d	Prints: 1,2,3,4,5,3	The expression can be simplified as follows: j = 1 + ((2 * 3) % 4) + 5 = 8. The original expression is as follows: j = ++i + ++i * ++i % ++i + ++i. Step one. Evaluate the unary expressions from left to right: j = 1 + 2 * 3 % 4 + 5. Step two. Add parentheses to indicate operator precedence: j = 1 + ((2 * 3) % 4) + 5. Step three. Evaluate the inner most parentheses: j = 1 + (6 % 4) + 5. Repeat step three: j = 1 + 2 + 5. Repeat step three: j = 8. The argument of the print expression is: j%5. The result is: 8 % 5 = 3.
27	d	Prints: 3,1	Inside of method m2, the local variables i1 and i2 remain unchanged while the shadowed instance variables are changed.
28	a k	Prints: null Run-time error	The declaration A13[] a1 = new A13[1] declares a variable a1 that references an array that contains one component of type A13. The declaration A13[][] a2 = new A13[2][1] declares a variable a2 that references an array that contains two components of type A13[]. In other words, the array referenced by a2 contains two references to two subarrays of type A13[]. The size of each subarray is 1. The declaration A13[][][] a3 = new A13[3][3][3] declares a variable a3 that references an array that contains three components of type A13[][]. In other words, the array referenced by a3 contains three references to three subarrays of type A13[][]. The dimensions of the subarrays are 3 X 3. The dimensions of the array referenced by a3 are 3 X 3 X 3. The number of elements in the array referenced by a3 is 3 * 3 * 3 = 27 elements. Each of the three subarrays contains three components, where each is a reference to a subarray of type A13[]. Each of the 27 elements of the array referenced by a3 is a reference of type A13 that has been initialized to the default value of null. At line 7, a reference to the array referenced by a2 is assigned to each of the three components of the array referenced by a3, a3[0] = a3[1] = a3[2] = a2. Since the array referenced by a2 has dimensions 2 X 1, the array referenced by a3 now has dimensions 3 X 2 X 1. The number of elements is 6. An attempt to access any element beyond those 6 results in an exception at run-time.

No.

Answer

Remark

Prints: null

The System.out.print method prints the word null if the argument is a String reference that is null.

a b

abstract public

The modifier, abstract, is applicable to an interface declaration, but its use is strongly discouraged; because every interface is implicitly abstract. If an interface is declare public, then the compiler will generate an error if the class is not stored in a file that has the same name as the interface plus the extension .java. The modifier, static, is applicable to a member interface, but not to an interface that is not nested. The modifier, synchronized, is applicable only to concrete implementations of methods. The modifiers, transient and volatile, are applicable only to variables.

b d f

0x0000 to 0xffff 0 to 0177777 0 to 65535

A char is a 16 bit unsigned value; so none of the char values are negative and the minimum value is zero. The maximum value is 2¹⁶ - 1.

Prints: true,true

The sign of an integral numeric type is changed by inverting all of the bits and by adding one.

c d

3 4

This question demonstrates a variety of assignment conversions. The compiler will implicitly do a narrowing conversion for an assignment statement if the right hand operand is a compile time constant of type byte, short, char, or int and the value falls within the range of the variable on the left and if the variable on the left is of type byte, short, or char. In this case, variables s1 and c1 are not compile time constants so the compiler will not do an implicit narrowing conversion. However, variables s2 and c2 are compile time constants that fall within the range of the left hand operand. For more information, please see JLS section 5.2.

The internal data model can be read and modified only through accessor and mutator methods.

A class is not tightly encapsulated if the internal data model can be read and/or modified without working through accessor (i.e. get) and mutator (i.e. set) methods.

InterruptedException

The methods Object.wait, Thread.join and Thread.sleep name InterruptedException in their throws clauses.

Prints: A B C

The String instance referenced by s2 is passed to the m1 method by passing the value of the reference. The reference value used in method m1 is a local copy of the reference. If the local copy used in method m1 is changed, then the original reference variable in the main method remains unchanged.

Compile-time error at 1

At line 1, the invocation of the Math.min method produces a return value of type int. The variable b1 is of type short; so the assignment expression results in a compile-time error. The Math class declares four versions of the min method; each declares a pair of parameters of the same type. The parameter pair can be of type int, long, float or double. The return type is the same as the argument types. At run-time, the arguments might not match the declared parameter types; so one argument or both might require an implicit conversion to an acceptable type. If both arguments are of type byte, short or char, then both will be promoted to type int. If only one argument is of type byte, short or char, then it will be promoted to the type of the other argument. If both arguments are of type int, long, float or double but the types differ, then a primitive widening conversion will be applied to one of the two arguments.

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.

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.

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.

valueOf

TreeSet

The elements are not key/value pairs; so a Map is not a good choice. A List generally accepts duplicate elements. A Set stores a collection of unique objects; so any attempt to store a duplicate object is rejected. TreeSet stores elements in an order that is determined either by a Comparator or by the Comparable interface.

Prints: false,true,true

HashSet implements the Set interface, but not the Map interface. HashMap extends AbstractMap and implements the Map interface. Hashtable extends Dictionary and implements the Map interface.

a b

return 31; return getI1();

A hashCode method that returns the constant value 31 is consistent with the hash code contract. Even so, a hashCode method that returns the same value regardless of the internal state of the object is not very good, because it will cause hashtables to place every instance of the class in the same bucket. If the equals method determines that two instances are equal, then the two instances must produce the same hash code. For that reason, the hash code must not be calculated using fields that are not used to determine equality. In this case, the equals method determines equality based on the value of i1. The value of i2 is not used to determine equality; therefore, i2 can not be used to calculate the hash code.

The synchronized modifier is a method modifier and can not be applied to a field.

c d e

3 4 5

The abstract and final modifiers can be applied to a method local class declaration.

Prints: C

The boolean type variable, b, is initialized to true. The boolean expression of the first if statement, b = false, is a simple assignment expression that sets b to false. Always look carefully at the boolean expression of an if statement to verify that the expected equality operator (==) has not been replaced by the simple assignment operator (=).

Compile-time error at line 4.

Anytime a field is accessed from within a static context it is very important to verify that the field is also static. If the field is instead an instance variable then the result is a Compile-time error.

Prints: GFC206,GFC206

Type GFC207 is a subclass of types GFC206 and GFC205, so any of the four methods are applicable to the method invocation expression, m(gfc207, gfc207). The most specific of the four, m(GFC206 x, GFC206 y), is chosen. Type GFC206 is a subclass of type GFC205, and method m(GFC206 x, GFC206 y) is more specific than the other three, because any invocation of m(GFC206 x, GFC206 y) could also be handled by any of the other three without causing a compile-time type error.

Prints: ABCI

Suppose that a class extends a superclass, X, or implements an interface, X. The field access expression ((X)this).hiddenField is used to access the hidden field, hiddenField, that is accessible within the superclass or interface, X.

G.this.s1

The qualified this expression ClassName.this.name can be used to access shadowed variables declared within an enclosing class.

Compile-time error

The declarations of b1 and c1 cause compile-time errors, because a reference of a subclass type can not refer to an instance of the superclass type.

c e

3 5

Local method variables and method parameters are stored on the stack and go out of scope after the method is exited. Although a local reference variable is stored on the stack, the referenced object is stored on the heap; so the object can continue to exist long after the method runs to completion. An object that is instantiated within a method or block is not permitted to refer to a variable that is declared within the method or block unless the variable is declared final and the variable declaration precedes the creation of the object.

Prints: 1,2,3,4,5,3

The expression can be simplified as follows: j = 1 + ((2 * 3) % 4) + 5 = 8. The original expression is as follows: j = ++i + ++i * ++i % ++i + ++i. Step one. Evaluate the unary expressions from left to right: j = 1 + 2 * 3 % 4 + 5. Step two. Add parentheses to indicate operator precedence: j = 1 + ((2 * 3) % 4) + 5. Step three. Evaluate the inner most parentheses: j = 1 + (6 % 4) + 5. Repeat step three: j = 1 + 2 + 5. Repeat step three: j = 8. The argument of the print expression is: j%5. The result is: 8 % 5 = 3.

Prints: 3,1

Inside of method m2, the local variables i1 and i2 remain unchanged while the shadowed instance variables are changed.

a k

Prints: null Run-time error

The declaration A13[] a1 = new A13[1] declares a variable a1 that references an array that contains one component of type A13. The declaration A13[][] a2 = new A13[2][1] declares a variable a2 that references an array that contains two components of type A13[]. In other words, the array referenced by a2 contains two references to two subarrays of type A13[]. The size of each subarray is 1. The declaration A13[][][] a3 = new A13[3][3][3] declares a variable a3 that references an array that contains three components of type A13[][]. In other words, the array referenced by a3 contains three references to three subarrays of type A13[][]. The dimensions of the subarrays are 3 X 3. The dimensions of the array referenced by a3 are 3 X 3 X 3. The number of elements in the array referenced by a3 is 3 * 3 * 3 = 27 elements. Each of the three subarrays contains three components, where each is a reference to a subarray of type A13[]. Each of the 27 elements of the array referenced by a3 is a reference of type A13 that has been initialized to the default value of null. At line 7, a reference to the array referenced by a2 is assigned to each of the three components of the array referenced by a3, a3[0] = a3[1] = a3[2] = a2. Since the array referenced by a2 has dimensions 2 X 1, the array referenced by a3 now has dimensions 3 X 2 X 1. The number of elements is 6. An attempt to access any element beyond those 6 results in an exception at run-time.

Dan Chisholm's Java Programmer Certification Mock Exam

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Java Programmer Certification Mock Exam