// File: BuggyList.java // Author: Geoffrey Tien/ Rita Ester // Description: Bug

Question

// File: BuggyList.java
// Author: Geoffrey Tien/ Rita Ester
// Description: Buggy linked list implementation for CSCI 225 Lab 1
// Based on SimpleStack at course website

public class BuggyList
{
// private inner Node class
private class Node
{
// all members public, for convenience
public int data;
public Node next;

// parameterized constructor
public Node(int x, Node nd)
{
data = x;
next = nd;
}
}
  
// private member variables
private int n; // number of items in list
private Node front; // front of list
private Node back; // back of list
  
// public member functions
  
// default constructor
public BuggyList()
{
n = 0;
front = null;
back = null;
}
  
// copy constructor
public BuggyList(BuggyList ls)
{
Node nd = ls.front;
while (nd != null)
{
addBack(nd.data);
}
}
  
// Inserts an int to the front of list
// PARAM: x is the value to be inserted
public void addFront(int x)
{
Node nd = new Node(x, front);
front = nd;
}
  
//Inserts an int to the back of list
// PARAM: x is the value to be inserted
public void addBack(int x)
{
Node nd = new Node(x, null);
back = nd;
n++;
}
  
// Removes and returns the item at the front of list
// Returns -1 if the list is empty (in lieu of proper exception handling)
public int removeFront()
{
Node nd = front;
front = front.next;
n--;
return nd.data;
}
  
// Returns the item at the specified index
//Returns -1 if the list is empty (in lieu of proper exception handling)
public int elementAt(int index)
{
if (n < 0) return -1;
else
{
Node nd = front;
// iterate to index
for (int i = 0; i < index; i++)
{
nd = front.next;
}
return nd.data;
}
}
  
// Returns the number of items in the list
public int count()
{
return n;
}
  
// Returns true if the list contains no items
public boolean isEmpty()
{
return (n == 0);
}
}

// File: CSCI225Lab1Driver.java
// Author: Geoffrey Tien/ Rita Ester
// Description: Driver file with main method for CSCI 225 Lab 1

public class CSCI225Lab1Driver
{
public static void main(String[] args)
{
int errorcount = 0;
boolean result = false;
// create a new list and test if empty
System.out.print("Creating new list and testing if empty... ");
BuggyList listA = new BuggyList();
result = listA.isEmpty();
if (result)
System.out.println("done - OK!");
else
{
System.out.println("ERROR: list not empty");
errorcount++;
}
  
// add 3 items to front of list
System.out.print("Using AddFront to add 3 items to front of list... ");
listA.addFront(12);
listA.addFront(9);
listA.addFront(4);
System.out.print("done. Checking if list is empty... ");
result = listA.isEmpty();
if (result)
{
System.out.println("ERROR: IsEmpty returned true");
errorcount++;
}
else
System.out.println("done - OK!");
System.out.print("Checking size of list... ");
result = listA.count() == 3;
if (result)
System.out.println("done - OK!");
else
{
System.out.println("ERROR: list size should be 3");
errorcount++;
}
// add two items to back of list
System.out.print("Using AddBack to add 2 items to back of list... ");
listA.addBack(17);
listA.addBack(26);
System.out.print("done. Checking value of item at index 1... ");
result = listA.elementAt(1) == 9;
if (result)
System.out.println("done - OK!");
else
{
System.out.println("ERROR: ElementAt(1) should be 9");
errorcount++;
}
System.out.print("Checking value of item at index 2... ");
result = listA.elementAt(2) == 12;
if (result)
System.out.println("done - OK!");
else
{
System.out.println("ERROR: ElementAt(2) should be 12");
errorcount++;
}
System.out.print("Checking value of item at index 3... ");
result = listA.elementAt(3) == 17;
if (result)
System.out.println("done - OK!");
else
{
System.out.println("ERROR: elementAt(3) should be 17");
errorcount++;
}
System.out.print("Checking value of item at index 4... ");
result = listA.elementAt(4) == 26;
if (result)
System.out.println("done - OK!");
else
{
System.out.println("ERROR: ElementAt(4) should be 26");
errorcount++;
}
  
// Create a new list and attempt to remove from it
System.out.print("Creating a new list... ");
BuggyList listB = new BuggyList();
System.out.print(" done. Attempting to remove an item from front... ");
int value = listB.removeFront();
// Add 3 elements using AddBack
System.out.print("Using AddBack to add 2 items to back of list... ");
listB.addBack(23);
listB.addBack(37);
listB.addBack(49);
System.out.print("Checking value of item at index 2... ");
result = listB.elementAt(2) == 49;
if (result)
System.out.println("done - OK!");
else
{
System.out.println("ERROR: ElementAt(2) should be 49");
errorcount++;
}
System.out.println("Test program complete. Detected " + errorcount + " errors.");
}
}

CSCI 225 Lab exercise 1 Debugging with an IDE In this lab you will be given a segment of Java code which contains a number of run-time bugs. Using the debugging features of the Eclipse IDE, you will identify and correct these errors. Download the BuggyList.java and CSCI225Lab1Driver.java files from C4 and add them to a new Java project in Eclipse. Build and run the program - it should terminate with a NullPointerException, but the console will indicate a number of errors before that point. Read the error descriptions carefully they are often quite descriptive of the problem, so you should learn and recognize the common errors and how to correct them. Java Debugging with Eclipse Tutorial by Lars Vogella. Setting breakpoints A breakpoint can be set at a line of code where you want program execution to pause automatically when debugging To set a breakpoint, position your mouse to the left of the line number of the location where you want the program to pause, and left double-click. A blue dot should appear next to the line number. To remove a breakpoint, left double-click on the blue dot After setting breakpoints start the program in debug mode (Debug As Java Application ). The Debug perspective with a set of views opens. Breakpoints and stepping When the program is running in debug mode and paused at a breakpoint, you can advance execution using step controls. a) Step into - if the currently highlighted line contains a method call, this allows you to highlight the first line of that method and begin step-by-step execution from that method Step over - this allows you to execute the next line in the current method. Step return -this executes all remaining lines in the current method, and step-by-step execution can resume from the point where the current method was called. b) c) Variables In the Debug perspective, there is a window labeled "Variables". This allows you to inspect the values of all global and local variables in a tree-like structure. Arrays and reference-based structures can be expanded to inspect individual elements; objects can be expanded to inspect their member attributes Using these controls, find and correct the errors in the BuggyList.java file. Submit your corrected file to C4 for lab participation credit. Deliverables Your BuggyList.java file with the errors corrected

Explanation / Answer

Please revert back if you need any other help

Code

// File: BuggyList.java

// Author: Geoffrey Tien/ Rita Ester

// Description: Buggy linked list implementation for CSCI 225 Lab 1

// Based on SimpleStack at course website

public class BuggyList {

// private inner Node class

private class Node {

// all members public, for convenience

public int data;

public Node next;

// parameterized constructor

public Node(int x, Node nd) {

data = x;

next = nd;

}

}

// private member variables

private int n; // number of items in list

private Node front; // front of list

private Node back; // back of list

// public member functions

// default constructor

public BuggyList() {

n = 0;

front = null;

back = null;

}

// copy constructor

public BuggyList(BuggyList ls) {

Node nd = ls.front;

while (nd != null) {

addBack(nd.data);

}

}

// Inserts an int to the front of list

// PARAM: x is the value to be inserted

public void addFront(int x) {

Node nd = new Node(x, front);

front = nd;

//incrementing the count of nodes after adding

n++;

}

// Inserts an int to the back of list

// PARAM: x is the value to be inserted

public void addBack(int x) {

//checking if list is empty adding at front and marking front as new node

if(front ==null)

{

Node d = new Node(x, null);

front = d;

n++;

}

else

{

//traversing till end to add

Node nd = front;

for (int i = 0; i < n - 1; i++) {

nd = nd.next;

}

Node d = new Node(x, null);

nd.next = d;

back = nd.next;

n++;

}

}

// Removes and returns the item at the front of list

// Returns -1 if the list is empty (in lieu of proper exception handling)

public int removeFront() {

//checking if list is empty

if(n ==0)

{

System.out.println("List is Empty");

return -1;

}

Node nd = front;

front = front.next;

n--;

return nd.data;

}

// Returns the item at the specified index

// Returns -1 if the list is empty (in lieu of proper exception handling)

public int elementAt(int index) {

//checking for invalid index

if (n < 0 || index > n - 1)

return -1;

else {

Node nd = front;

// iterate to index

for (int i = 0; i < index; i++) {

//incrementing nd as front will remain same

nd = nd.next;

}

return nd.data;

}

}

// Returns the number of items in the list

public int count() {

return n;

}

// Returns true if the list contains no items

public boolean isEmpty() {

return (n == 0);

}

// prints the list

public void print() {

Node nd = front;

System.out.println();

for (int i = 0; i < n; i++) {

System.out.print(nd.data + " ");

nd = nd.next;

}

System.out.println();

}

}

Sample Output

Creating new list and testing if empty... done - OK!

Using AddFront to add 3 items to front of list...

4 9 12

done.

Checking if list is empty... done - OK!

Checking size of list... done - OK!

Using AddBack to add 2 items to back of list...

4 9 12 17 26

done.

Checking value of item at index 1... done - OK!

Checking value of item at index 2... done - OK!

Checking value of item at index 3... done - OK!

Checking value of item at index 4... done - OK!

Creating a new list... done. Attempting to remove an item from front... List is Empty

Using AddBack to add 2 items to back of list... Checking value of item at index 2... done - OK!

Test program complete. Detected 0 errors.

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