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Doug Wolfinger

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since Jul 27, 2002

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Recent posts by Doug Wolfinger

Tomcat Configuration

Hmm. So they just have to be up to date with a questionable version of an operating system that replaces Win98, which I personally have never had any problems with. But they're happy to stick with a jvm that's 3 or 4 years old? If you can download an older version of tomcat, why can't you download a newer version of the jdk? I've read that all sorts of things change with tomcat when using an IDE with java, instead of dos, and I've never used one, so I won't be of much more use.
HOWEVER, I've heard that 4.0.3 has a bug when working with RMI. The other older versions might have all sorts of other bugs...

22 years ago

Tomcat Configuration

My 4.1.18 runs fine on Win98, and I didn't do any modifications, except setting JAVA_HOME in autoexec. Does it run differently on xp? Also does this latest version run on jdk1.2.2? I'd consider upgrading the jvm.

22 years ago

displaying sql query results

The connection syntax was given to me by the webhost, and I'm positive that my database userid and password are correct. Should I ask the webhost what is going wrong? I'm not sure what you mean by quotes around html tags because the br tag does have quotes around it in the out.print statement.
Thanks!

22 years ago

JDBC and Relational Databases

displaying sql query results

I tried the if statement with the do-while as well as the SELECT *, but am still getting the same output. My DBTools shows me those tables have the data. What could be going wrong? Thanks again.

22 years ago

JDBC and Relational Databases

displaying sql query results

nudge, nudge

22 years ago

JDBC and Relational Databases

displaying sql query results

Hello,
I am trying to print the results of a simple query. ITEM is the first of four columns in my table, and is the only one I want to see the results from. But the browser only displays the basic info from the jsp code near the top of the program when I enter the url. I have marked the SELECT statement with a comment. Thanks!
The output...
MySQL-JSP, hello.delete mm.mysql.libdelete mm.mysql-2.0.3.lib
hello world
The current data and time isSun Dec 29 21:06:50 PST 2002 after DriverManager con!=null;1
after show table
con!=null;

<html>
<head>
<title>my first mysql jsp</title>
</head>
<body>MySQL-JSP, hello.delete mm.mysql.libdelete mm.mysql-2.0.3.lib
<br>hello world
<br>The current data and time is<%= new java.util.Date()
%>
<%@page language="java" import="java.sql.*"%>
<% Connection con = null;
try
{
Class.forName("Driver").newInstance();
System.out.println("JDBC driver loaded");
} catch (Exception E)
{
System.err.println("Unable to load driver.");
E.printStackTrace();
}
con = DriverManager.getConnection( "jdbc:mysql://localhost/dbasename?user=dbaseuid&password=dbpasswd");%>after DriverManager
<% if(con==null)
{
%>
con=null;2<br>
<% System.out.println("con=null");
} if(con!=null)
{
%> con!=null;1<br>
<% System.out.println("con!=null");
}
/* } catch(SQLException cnfe)
{ cnfe.printStackTrace();
} catch(Exception e)
{ e.printStackTrace();
}
*/ if(con==null){%>con=null;3<br>
<% System.out.println("con=null");
}
//THIS IS THE QUERY
try
{
Statement stmt = con.createStatement();
ResultSet resultset;
resultset = stmt.executeQuery("SELECT F.Item, NF.Item "
+ "FROM FOOD F, NONFOOD NF");
// + " WHERE F.Need = 'Yes' AND WHERE "
// + "NF.Need = 'Yes'");
while(resultset.next())
{
out.print("I need: " + resultset.getString("Item")); // WHY WON'T THIS PRINT?
out.print("<br>");
}
resultset.close();
//String upd = "CREATE TABLE new(Author_ID INTEGER NOT NULL PRIMARY KEY,Author_name CHAR(50));";
// stmt.executeUpdate(upd);
} catch(SQLException cnfe)
{ cnfe.printStackTrace();
} catch(Exception e)
{
%> con=null;4<br>
<% e.printStackTrace();
}
%> after show table<br>
<% try
{
if(con!=null) {
%> con!=null;<br>
<% con.close();
}
} catch(SQLException sqle)
{
System.out.println("Unable to close database connection."); }
%>
</body>
</html>

[ December 29, 2002: Message edited by: Doug Wolfinger ]

22 years ago

JDBC and Relational Databases

Converting class code back to source code

Thanks, all. I have a beta Mocha installed but can't get it to work, so I used DJ. The decompilation was very pleasant but I noticed some disturbing things afterwards. For one thing, I couldn't get into my c:\ where the executable was located after the decompilation. It was alarming. The software locked up the c:\ somehow. So I closed Win Explorer and everything was fine when I reopened it. And I noticed that all class files had the DJ icon. I decided to get rid of it, and deleted the DJ files that made all the class files associate with it.
I didn't realize the source code would be neatly formatted by the decompiler, so that was a nice surprise.
If the new version of Mocha works I might go with that; it operates from the dos command line, so it should be less obtrusive.
[ November 19, 2002: Message edited by: Doug Wolfinger ]

22 years ago

Converting class code back to source code

Please help! I ran a program and redirected the output to a flat file, but I named that file the same as the program name. So I overwrote my program, Selection.java, with the text of the output by saying java Selection > selection.java. Anyone know the DOS command to convert the .class file back to the .java file?
EDIT: I'll try to find a decompiler at downloads.com. Isn't javap supposed to do this? It does something, but it doesn't create the .java file when I run it in \bin.
Thanks,
Doug
[ November 18, 2002: Message edited by: Doug Wolfinger ]
[ November 18, 2002: Message edited by: Doug Wolfinger ]

22 years ago

Picking characters from a string

My bad. I've copied this to the Intermediate forum.

22 years ago

Selecting characters from a string

Hello,
I've copied this from the Beginners forum, as I malignantly

posted it there originally.
I am trying to pass a string that represents a postfix expression. The method that accepts it should take each number and place it on the stack. When it encounters an operator, it should pop the top two numbers and evaluate them with the operator.
This is the expression. "abc+-"
a=7, b=3, c=12 So it applies "+" to c and b, then it subtracts (c + b) from a. I have made the string into a string array in my program, but I think the idea is to pass the expression as a regular string as I have it above. I would use substring(), but that doesn't work with a number larger than 2 digits. Thanks!

class PostFixStack {
StackArrayBased stack = new StackArrayBased();
String operator;
int operand1;
int operand2;
int result; //primitive value which is converted to Integer
Integer intObj; //Integer to hold string value
Integer intOper1; //used to pop from stack
Integer intOper2; //used to pop from stack
Integer intResult; //used to convert from result to Integer and push to stack
public Integer srMeth(String[] str)
//Accepts a postfix expression as an argument. Processes the expression.
//Precondition: str.length() > 0.
//Postcondition: Returns the Integer that results from the expression str.
{
for(int i=0;i<str.length;i++)
{
if( str[i].equals("*") || str[i].equals("-") || str[i].equals("+") ) {
operator = str[i];
intOper1 = (Integer)stack.pop();
intOper2 = (Integer)stack.pop();
operand2 = intOper2.intValue();
operand1 = intOper1.intValue();
if(operator.equals("*"))
result = (operand2 * operand1);
if(operator.equals("+"))
result = (operand2 + operand1);
if(operator.equals("-"))
result = (operand2 - operand1);
//convert result back to an Integer so that push() will accept it.
intResult = new Integer(result);
stack.push(intResult);
System.out.println("currently the top value is " + stack.peek());
}
//if the array occurrence is a number
else {
System.out.println(str[i]);
intObj = new Integer(str[i]);
stack.push((Integer)intObj);
}
}
return intResult;
}
public static void main(String args[]) {
String string[] = {"7","3","12","+","-"};
String stringB[] = {"7","3","12","-","-5","*","+"};
PostFixStack pfs = new PostFixStack();
System.out.println(pfs.srMeth(string) + " = the value of the 9a expression");
System.out.println(pfs.srMeth(stringB) + " = the value of the 9b expression");
}
}
If you would like to use that program, you'll need this one as well.
[code]
public class StackArrayBased
implements StackInterface {
final int MAX_STACK = 50; // maximum size of stack
private Object items[];
private int top;
public StackArrayBased() {
items = new Object[MAX_STACK];
top = -1;
} // end default constructor
public boolean isEmpty() {
return top < 0;
} // end isEmpty
public boolean isFull() {
return top == MAX_STACK-1;
} // end isFull
public void push(Object newItem) throws StackException {
if (!isFull()) {
items[++top] = newItem;
}
else {
throw new StackException("StackException on " +
"push: stack full");
} // end if
} // end push
public void popAll() {
items = new Object[MAX_STACK];
top = -1;
} // end popAll
public Object pop() throws StackException {
if (!isEmpty()) {
return items[top--];
}
else {
throw new StackException("StackException on " +
"pop: stack empty");
} // end if
} // end pop
public Object peek() throws StackException {
if (!isEmpty()) {
return items[top];
}
else {
throw new StackException("Stack exception on " +
"peek - stack empty");
} // end if
} // end peek
} // end StackArrayBased

22 years ago

Java in General

Picking characters from a string

Hello,
I am trying to pass a string that represents a postfix expression. The method that accepts it should take each number and place it on the stack. When it encounters an operator, it should pop the top two numbers and evaluate them with the operator.
This is the expression. "abc+-"
a=7, b=3, c=12 So it applies "+" to c and b, then it subtracts (c + b) from a. I have made the string into a string array in my program, but I think the idea is to pass the expression as a regular string as I have it above. Thanks!

class PostFixStack {
StackArrayBased stack = new StackArrayBased();
String operator;
int operand1;
int operand2;
int result; //primitive value which is converted to Integer
Integer intObj; //Integer to hold string value
Integer intOper1; //used to pop from stack
Integer intOper2; //used to pop from stack
Integer intResult; //used to convert from result to Integer and push to stack
public Integer srMeth(String[] str)
//Accepts a postfix expression as an argument. Processes the expression.
//Precondition: str.length() > 0.
//Postcondition: Returns the Integer that results from the expression str.
{
for(int i=0;i<str.length;i++)
{
if( str[i].equals("*") || str[i].equals("-") || str[i].equals("+") ) {
operator = str[i];
intOper1 = (Integer)stack.pop();
intOper2 = (Integer)stack.pop();
operand2 = intOper2.intValue();
operand1 = intOper1.intValue();
if(operator.equals("*"))
result = (operand2 * operand1);
if(operator.equals("+"))
result = (operand2 + operand1);
if(operator.equals("-"))
result = (operand2 - operand1);
//convert result back to an Integer so that push() will accept it.
intResult = new Integer(result);
stack.push(intResult);
System.out.println("currently the top value is " + stack.peek());
}
//if the array occurrence is a number
else {
System.out.println(str[i]);
intObj = new Integer(str[i]);
stack.push((Integer)intObj);
}
}
return intResult;
}
public static void main(String args[]) {
String string[] = {"7","3","12","+","-"};
String stringB[] = {"7","3","12","-","-5","*","+"};
PostFixStack pfs = new PostFixStack();
System.out.println(pfs.srMeth(string) + " = the value of the 9a expression");
System.out.println(pfs.srMeth(stringB) + " = the value of the 9b expression");
}
}

If you would like to use that program, you'll need this one, too.

public class StackArrayBased
implements StackInterface {
final int MAX_STACK = 50; // maximum size of stack
private Object items[];
private int top;
public StackArrayBased() {
items = new Object[MAX_STACK];
top = -1;
} // end default constructor
public boolean isEmpty() {
return top < 0;
} // end isEmpty
public boolean isFull() {
return top == MAX_STACK-1;
} // end isFull
public void push(Object newItem) throws StackException {
if (!isFull()) {
items[++top] = newItem;
}
else {
throw new StackException("StackException on " +
"push: stack full");
} // end if
} // end push
public void popAll() {
items = new Object[MAX_STACK];
top = -1;
} // end popAll
public Object pop() throws StackException {
if (!isEmpty()) {
return items[top--];
}
else {
throw new StackException("StackException on " +
"pop: stack empty");
} // end if
} // end pop
public Object peek() throws StackException {
if (!isEmpty()) {
return items[top];
}
else {
throw new StackException("Stack exception on " +
"peek - stack empty");
} // end if
} // end peek
} // end StackArrayBased

22 years ago

need help with compareTo()

Hi,
I am still trying to figure out this method compareTo.
Node2.java implements Comparable. So, in using Node2 to cast in the comparison, I would think that I'm fulfilling the obligation to use a Comparable object to do that. Everything I am comparing is an Object, so I can't see what the problem is. The 3 compiler errors are "can't resolve symbol."
Thanks!
Here is Node2, which contains the compareTo method, making the Node2 type Comparable.

public class Node2 implements Comparable {
private Object item;
private Node2 next;
private Integer firstName;
private Integer lastName;
public Node2() {}
public Node2(Integer first, Integer last) {
firstName = first;
lastName = last;
}
public Node2(Object newItem) {
item = newItem;
next = null;
} // end constructor
public Node2(Object newItem, Node2 nextNode2) {
item = newItem;
next = nextNode2;
} // end constructor
public void setItem(Object newItem) {
item = newItem;
} // end setItem
public Object getItem() {
return item;
} // end getItem
public void setNext(Node2 nextNode2) {
next = nextNode2;
} // end setNext
public Node2 getNext() {
return next;
} // end getNext
public int compareTo(Object rhs)
{
//returns 0 if all fields match
// if lastName equals rhs.lastName and
// firstName is greater than rhs.firstName
//returns -1 if lastName is less than rhs.lastName or
// if lastName equals rhs.lastName and
// firstName is less than rhs.firstName
if (lastName.compareTo(((Node2)rhs).lastName)==0) {
System.out.println("from the compareTo meth " + firstName + " is first name ");
return firstName.compareTo(((Node2)rhs).firstName);
}
else {
return lastName.compareTo(((Node2)rhs).lastName);
}
}
} // end class Node2

Here is Noding6, which extends Node2 and implements compareTo.

class Noding6 extends Node2 {
//this is needed to make the object in main()
public Noding6() {}
Node2 newValue = new Node2(new Integer(16));
Node2 n1, n2, n3, n4, n5;
private Node2 head;
private Node2 tail;
private Node2 list; //to reference the last Node2 in a circular list
private Node2 curr;
private Node2 prev;
private Node2 nextNode2;
private Node2 getCurr; //used to retrieve a Node2 by specified index in find(int)
private Object currNode2;
private Object nextNode2Comp;
public Noding6(Object first, Object last)
{
currNode2 = first;
nextNode2Comp = last; //last is the next node that is already in the list
}
public Node2 Node2Meth()
{
n5 = new Node2(new Integer(84));
n4 = new Node2(new Integer(13),n5);
n3 = new Node2(new Integer(1),n4);
n2 = new Node2(new Integer(5),n3);
n1 = new Node2(new Integer(9),n2);
int i;
n4.setNext(n5);
n3.setNext(n4);
n2.setNext(n3);
n1.setNext(n2); //link the Node2s
head = n1;
curr = head;
return curr;
}
public void tryCompare()
{
n1.getItem();
head = head.getNext();
for ( prev = null, curr = head; (curr != null)
&& (newValue.compareTo(curr.getItem()) > 0);
prev = curr, curr = curr.getNext() ) {
System.out.println("newValue > current item");
}
}
public int compareTo(Object rhs)
{
// returns 0 if all fields match
// if nextNode2 equals rhs.nextNode2 and
// currNode2 is greater than rhs.currNode2
// returns -1 if nextNode2 is less than rhs.nextNode2 or
// if nextNode2 equals rhs.nextNode2 and
// currNode2 is less than rhs.currNode2
currNode2 = (Node2)curr; // gets "incompatible types" error when currNode2 is defined as Integer
nextNode2Comp = (Node2)curr.getNext(); // gets "incompatible types" error when currNode2 is defined as Integer
if (currNode2.compareTo(((Node2)rhs).nextNode2Comp)==0){
System.out.println("from the compareTo meth " + currNode2 + " is currNode2");
return currNode2.compareTo(((Node2)rhs).nextNode2Comp);
}
else {
return currNode2.compareTo(((Node2)rhs).nextNode2Comp);
} // end if
} // end compareTo
public static void main(String args[]) {
Noding6 nod = new Noding6();
nod.Node2Meth();
nod.tryCompare();
}
}

[ October 18, 2002: Message edited by: Doug Wolfinger ]

22 years ago

Java in General

need help with compareTo()

Regarding the end of the loop, I suppose I could add
However, I'm now getting an "Incompatible types" compile error from the while statement in sortedAdd(). The compiler says "found: int" "required: boolean", and points to the paren that follows "compareTo". So I've got my work cut out for me.
Btw, how do I capture the console's output. I thought "javac pgmname.java > pgmname.txt" would places the output in the text file, but it's not working. Thanks!

22 years ago

Java in General

need help with compareTo()

I am trying to add String items to a sorted array list, using compareTo to find the proper position for each item.
This is the runtime error I get when I run ListPop.java with sortedAdd() defined with a String, instead of Object, in the argument list.
Exception in thread "main" java.lang.NullPointerException
at java.lang.String.compareTo(String.java:789)
at java.lang.String.compareTo(String.java:825)
at SortedList.sortedAdd(SortedList.java:41)
at ListPop.main(ListPop.java:17)
When I try to define sortedAdd() with an Object, instead of a String, in the argument list I get this error message when I compile SortedList.java
SortedList.java:41: cannot resolve symbol
symbol : method compareTo (java.lang.Object)
location: class java.lang.Object
while(item.compareTo((Object)arr[pos]) <= 0) {
1 error
Here is SortedList.java

class SortedList extends FullName implements SortedListInterface {
private static final int MAX_LIST = 50;
private Object arr[]; //a sorted array of list items
private int numItems;
public SortedList()
{
arr = new Object[MAX_LIST];
numItems = 0;
}
public boolean sortedIsEmpty()
{
//returns true if list has no items
return (numItems == 0);
}
public int sortedSize()
{
return numItems;
}
public void sortedAdd(int index, String item) throws
IndexOutOfBoundsException
{
int length = sortedSize();
int pos;
if (index > MAX_LIST) throw
new ListIndexOutOfBoundsException("index is too high");
//check for duplicity
for(pos = 0;pos <= length;pos++) {
if(item.equals(arr[index])) {
throw new SortedListDuplicityException(item + " is already in this sorted list");
}
}
if(length == 0) {
arr[0] = item;
numItems++;
}
else {
// for(pos=length;item < arr[pos];pos--) {
[B]while(item.compareTo((String)arr[pos]) <= 0)[/B] {
System.out.println("moving along");
}
arr[pos + 1] = item;
numItems++;
}
} //end sortedAdd
public Object sortedGet(int index)
{
int pos;
int length=sortedSize();
for (pos = 0;pos <= length;pos++) {
if (pos == index) {
return arr[pos];
}
// else {
}
return null;
/* if (pos == length) {
* throw new ItemNotFoundException("Item at position " + index + " not found");
* return null;
* }
*/ }
public void sortedRemove(int index)
{
int pos;
int length = sortedSize();
for(pos = index;pos <= length;pos++) {
arr[index] = arr[pos+1];
}
}
public int locatedIndex(Object item) throws ItemNotFoundException
{
//Locates the position of the item.
//precondition: none
//postcondition: The index of the object is returned if it exists in the
//list. If it does not exist and exception is thrown.
int length=sortedSize();
for(int i=0;i<=length;i++) {
if (arr[i] == item) {
return i;
}
else {
throw new ItemNotFoundException("that item is not in the list");
// return 0;
}
}
return 0;
}

Here is FullName.java, which implements compareTo()

Here is ListPop.java, which attempts to populate the array.

It should put the first item in the array here

so why is it giving me the NullPointerException for arr[]?
New ones should be added when the while loop in sortedAdd() finishes, right?
Thanks!
[ October 09, 2002: Message edited by: Doug Wolfinger ]
[ October 09, 2002: Message edited by: Doug Wolfinger ]

22 years ago

Java in General

Retrieving the first item in list

I've solved it. I should have had the for loop counting down

Thanks!

22 years ago