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Answers: Certified Java Programmer Mock Exam
No.AnswerRemark
1c  Prints: long,float,double  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.  
2b  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.  
3d  Prints: AZA  Instances of type String are immutable. In method m1, the replace method returns a new instance of type String that contains the value Y, but the String instance referenced by s1 remains unchanged. The original value, A, is printed in method m1. In method m2, the replace method returns a new instance of type String that contains the value Z, and a reference to the new instance is assigned to reference variable s1. The new value, Z, is printed in method m2. In the main method, a copy of the reference value contained by the reference variable s1 is passed as an argument to methods m1 and m2. Since String instances are immutable, methods m1 and m2 can not change the original String instance that is declared in the main method. Since references are passed by value, methods m1 and m2 can not change the reference variable declared in the main method. Regardless of anything that happens in methods m1 and m2, the reference variable s1 that is declared in the main method will continue to reference the original String instance that contains the value A.  
4d  Prints: double  The Math.random method returns a value of type double. The range of values is greater than or equal to zero and less than one.  
5b  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.  
6d  Prints: ABAbAb  Instances of type String are immutable. In method m1, the toUpperCase method returns a new instance of type String that contains the value AB, and a reference to the new instance is assigned to reference variable s1. The new value, AB, is printed in method m1. In method m2, the toLowerCase method returns a new instance of type String that contains the value ab, but the String instance referenced by s1 remains unchanged. The original value, Ab, is printed in method m2. In the main method, a copy of the reference value contained by the reference variable s1 is passed as an argument to methods m1 and m2. Since String instances are immutable, methods m1 and m2 can not change the original String instance that is declared in the main method. Since references are passed by value, methods m1 and m2 can not change the reference variable declared in the main method. Regardless of anything that happens in methods m1 and m2, the reference variable s1 that is declared in the main method will continue to reference the original String instance that contains the value Ab.  
7e  Compile-time error  The Math.random method does not accept a seed value. If your application requires a seed, then use java.util.Random.  
8d  Prints: 1212  The reference variable s3 is initialized with a reference to an instance of type String containing the value "12". The expression s1 += s2 is equivalent to the expression s1 = s1 + s2. Further simplification produces s1 = "1" + "2" = "12". The expression s3 += s1 is equivalent to the expression s3 = "12" + "12" = "1212".  
9d  Prints: double,double,double  The Math.sin, Math.cos and Math.tan methods return a value of type double.  
10b  Prints: false,true  The reference variable s1 is initialized with a reference to an instance of type String containing the value "ABCDEFG". The reference variable s2 is initialized with a reference to an instance of type String containing the value "EFGHIJ". The expression s3 = s1.substring(4,7) initializes the reference variable s3 with a reference to a unique instance of type String containing the value "EFG". The expression s4 = s2.substring(0,3) initializes the reference variable s4 with a reference to a unique instance of type String containing the value "EFG". The expression s3 == s4 compares two unique reference values and produces the value false even though s3 and s4 reference two String instances that contain the same value, "EFG". The expression s3 + s4 produces a unique instance of type String containing the value "EFGEFG". Similarly, the expression s4 + s3 produces a unique instance of type String containing the value "EFGEFG". The expression (s3 + s4).equals(s4 + s3) compares the contents of two unique instances of type String that contain the value "EFGEFG". The result of the comparison is true.  
11a  g  h  i  b1  b7  b8  b9  The Math.random method returns a value that is equal to or greater than zero and less than 1.0.  
12d  Prints: "ABCDEF"  The reference variable s1 is initialized with a reference to an instance of type String containing the value "ABCDEFG". The expression s2 = s1.substring(0,3) initializes the reference variable s2 with a reference to a unique instance of type String containing the value "ABC". The expression s3 = s1.substring(4,6) creates a unique instance of type String containing the value "EF". The expression c1 = s1.charAt(3) initializes the primitive variable c1 with the value 'D'. The expression String.valueOf(c1) invokes the static valueOf method with an argument of type primitive char and value 'D'. The valueOf method creates a new instance of type String. The value contained by the new instance is "D". The expression s2.concat(String.valueOf(c1)) invokes the concat method on the instance of type String referenced by the variable s2. The instance referenced by s2 contains the value "ABC". The value contained by the argument is "D". The result of the concatenation operation is a new instance of type String containing the value "ABCD". The expression s2.concat(String.valueOf(c1)).concat(s3) invokes the concat method on the previously created instance containing the value "ABCD". The instance referenced by the argument s3 contains the value "EF". The result of the concatenation operation is a new instance of type String containing the value "ABCDEF".  
13l  None of the above  All methods of the java.lang.Math class are static.  
14a  d  e  abs  max  min   
15f  Prints: DDDLDD  The round method does not return either of the two floating point primitive types, float or double. The ceil, sin and sqrt methods return only a value of type double. The abs and max methods are able to return an int, long, float or double depending on the argument type.  
16e  f  5  6  The overloaded contructors for the String class accept a parameter of type String or StringBuffer or an array of byte or char. There is no constructor that will accept a primitive byte or char. Please note that if you want to convert a primitive to a String then you can use the static String.valueOf method.  
17e  Prints: DDDD  The floor and ceil methods are not overloaded. There is only one version of each method. The parameter type is double, and the return type is double.  
18e  Prints: AB C D EF  The trim method creates a new String instance with the leading and trailing white space removed.  
19d  Prints: 12,true  The valueOf method returns a String representation of the input parameter. The input parameter may be of type Object, char[], or any primitive type. The toString method returns a reference to the existing String instance. It does not create a new instance of the String.  
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