Java Certification Question 0055

What will happen when you attempt to compile and run the following code?

public class Agg{

static public long i=10;

public static void main(String argv[]){

switch(i){

default:

System.out.println("no value given");

case 1:

System.out.println("one");

case 10:

System.out.println("ten");

case 5:

System.out.println("five");

}

}

}

1) Compile time error
2) Output of "ten" followed by "five"
3) Output of "ten"
4) Compilation and run time error because of location of default

Answer 1:

1) Compile time error

This might be considered a "gocha" or deliberate attempt to mislead you because i has been given the data type of long and the parameter must be either a byte, char, short or int. If you attempt to compile this code with JDK 1.2 you will get an error that says something like "Incompatible type for switch, Explicit cast needed to convert long to int. Answering with option 2 would have been reasonable because if the parameter had been an integer type the lack of break statements would have caused this output. If you gave either of the answers you should probably revise the subject.

Java Certification Question 0054

What will happen when you attempt to compile and run the following code?

public class Inc{

public static void main(String argv[]){

Inc inc = new Inc();

int i =0;

inc.fermin(i);

i = i++;

System.out.println(i);

}

void fermin(int i){

i++;

}

}

1) Compile time error
2) Output of 2
3) Output of 1
4) Output of 0

Answer 4:

4) Output of 0

The method fermin only receives a copy of the variable i and any modifications to it are not reflected in the version in the calling method. The post increment operator ++ effectivly modifes the value of i after the initial value has been assiged to the left hand side of the equals operator. This can be a very tricky conept to understand

Java Certification Question 0053

You need to read in the lines of a large text file containing tens of megabytes of data. Which of the following would be most suitable for reading in such a file

1) new FileInputStream("file.name")
2) new InputStreamReader(new FileInputStream("file.name"))
3) new BufferedReader(new InputStreamReader(new FileInputStream("file.name")));
4) new RandomAccessFile raf=new RandomAccessFile("myfile.txt","+rw");

Answer 3:

3) new BufferedReader(new InputStreamReader(new FileInputStream("file.name")));

The key to this question is that it asks about tens of megabytes of data, implying that performance is an issue. A Buffered Reader will optimise the performance of accessing a file. Although the objectives do not specifically mention it questions on I/O do come up on the exam.

Java Certification Question 0052

You have been asked to create a scheduling system for a hotel and catering organsiation.

You have been given the following information and asked to create a set of classes to represent it.

On the catering side of the organsiation they have

Head Chefs
Chefs
Apprentice Chefs

The system needs to store an employeeid, salary and the holiday entitlement

How would you best represent this information in Java

1) Create classes for Head Chef, Chef, Apprentice Chef and store the other values in fields
2) Create an employee class and derive sub classes for Head Chef, Chef, Apprentice Chef and store the other values in fields.
3) Create and employee class with fields for Job title and fields for the other values.
4) Create classes for all of the items mentioned and create a container class to represent employees

Answer 3:

3) Create and employee class with fields for Job title and fields for the other values.

These questions can appear tricky as the whole business of designing class structures is more art than science. It is asking you to decide if an item of data is best represented by the "Is a" or "Has a" relationship. Thus in this case any of the job titles mentioned will always refer to something that "Is a" employee. However the employee "has a" job title that might change.

One of the important points is to ask yourself when creating a class "Could this change into another class at some point in the future". Thus in this example an apprentice chef would hope one day to turn into a chef and if she is very good will one day be head chef. Few other mock exams seem to have this type of questions but they di come up in the real exam.

Java Certification Question 0051

What will happen when you attempt to compile and run the following code

class Base{

protected int i = 99;

}

public class Ab{

private int i=1;

public static void main(String argv[]){

Ab a = new Ab();

a.hallow();

}

abstract void hallow(){

System.out.println("Claines "+i);

}

}

1) Compile time error
2) Compilation and output of Claines 99
3) Compilation and output of Claines 1
4) Compilation and not output at runtime

Answer 1:

1) Compile time error

When compiled with JDK 1.1 the following error is produced.

Abstract and native methods can't have a body: void hallow() abstract void hallow()