Head First java chap 5 doesn't compile

[Nicole Munneke]

Hi everyone,

I'm starting to learn Java with the Head First Java book (my manager at work gave me the book), but I get stuck at chapter 5.
I write the code in Notepad++ and compile it in commandprompt.
I'm supposed to write the code for two classes, and copy the code for the third class. I can also copy the code for all three classes, leaving me with the same error.
The error: Could not find or load main class SimpleDotCom
Could not find or load main class Game
Could not find or load main class GameHelper

The code is in three different files.
The code:

package chap05;
import helpers.GameHelper;
import java.util.Scanner;
public class Game {
public static void main(String[] args)
{
int numOfGuesses = 0;
GameHelper helper = new GameHelper();
SimpleDotCom theDotCom = new SimpleDotCom();
int randomNum = (int) (Math.random() * 5);
int[] locations = {randomNum, randomNum+1, randomNum+2};
theDotCom.setLocationCells(locations);
boolean isAlive = true;
while (isAlive == true)
{
String guess = helper.getUserInput("enter a number");
String result = theDotCom.checkYourself(guess);
numOfGuesses++;
if (result.equals("kill")) {
isAlive = false;
System.out.println("You took " + numOfGuesses + " guesses");
}
}
}
}

package chap05;
import java.io.*;
import java.util.*;
public class GameHelper {
private static final String alphabet = "abcdefg";
private int gridLength = 7;
private int gridSize = 49;
private int [] grid = new int[gridSize];
private int comCount = 0;
public String getUserInput(String prompt) {
String inputLine = null;
System.out.print(prompt + " ");
try {
BufferedReader is = new BufferedReader(
new InputStreamReader(System.in));
inputLine = is.readLine();
if (inputLine.length() == 0 ) return null;
} catch (IOException e) {
System.out.println("IOException: " + e);
}
return inputLine.toLowerCase();
}
public ArrayList<String> placeDotCom(int comSize) { // line 19
ArrayList<String> alphaCells = new ArrayList<String>();
String [] alphacoords = new String [comSize]; // holds 'f6' type coords
String temp = null; // temporary String for concat
int [] coords = new int[comSize]; // current candidate coords
int attempts = 0; // current attempts counter
boolean success = false; // flag = found a good location ?
int location = 0; // current starting location
comCount++; // nth dot com to place
int incr = 1; // set horizontal increment
if ((comCount % 2) == 1) { // if odd dot com (place vertically)
incr = gridLength; // set vertical increment
}
while ( !success & attempts++ < 200 ) { // main search loop (32)
location = (int) (Math.random() * gridSize); // get random starting point
//System.out.print(" try " + location);
int x = 0; // nth position in dotcom to place
success = true; // assume success
while (success && x < comSize) { // look for adjacent unused spots
if (grid[location] == 0) { // if not already used
coords[x++] = location; // save location
location += incr; // try 'next' adjacent
if (location >= gridSize){ // out of bounds - 'bottom'
success = false; // failure
}
if (x>0 & (location % gridLength == 0)) { // out of bounds - right edge
success = false; // failure
}
} else { // found already used location
// System.out.print(" used " + location);
success = false; // failure
}
}
} // end while
int x = 0; // turn good location into alpha coords
int row = 0;
int column = 0;
// System.out.println("\n");
while (x < comSize) {
grid[coords[x]] = 1; // mark master grid pts. as 'used'
row = (int) (coords[x] / gridLength); // get row value
column = coords[x] % gridLength; // get numeric column value
temp = String.valueOf(alphabet.charAt(column)); // convert to alpha
alphaCells.add(temp.concat(Integer.toString(row)));
x++;
// System.out.print(" coord "+x+" = " + alphaCells.get(x-1));
}
// System.out.println("\n");
return alphaCells;
}
}

package chap05;
public class SimpleDotCom {
int[] locationCells;
int numOfHits = 0;
public void setLocationCells(int[] locs)
{
locationCells = locs;
}
public String checkYourself(String stringGuess) {
int guess = Integer.parseInt(stringGuess);
String result = "miss";
for (int cell: locationCells)
{
if (guess == cell) {
result = "hit";
numOfHits++;
break;
}
}
if (numOfHits == locationCells.length)
{
result = "kill";
}
System.out.println(result);
return result;
}
}

Can someone please help me out?

[Naziru Gelajo]

The GameHelper class is in the chap5 package and not in the helpers package. That's why you are getting the error. Comment out the import helpers.GameHelper and see what happens

[Knute Snortum]

Welcome to the Ranch! Thank you for using code tags and formatting your code.

What command are you using on the command line and what directory are you in when you issue it? Remember that you have to be cd'd to the project root and using the "dot" name for the Java file.
cd /dir/that/has/chap05/in/it java chap05.SimpleDotCom

[Norm Radder]

Note also that the class referenced on the commandllne needs to have a main() method for the java program to find to start the program's execution.
Game is the only class I see with a main method.
So the command would be: java chap05.Game

[Nicole Munneke]

Thanks for your replies, sadly, it still doesn't work.
When trying to compile the Game.java (javac Game.java), I get the following errors:

Game.java:11: error: cannot find symbol
GameHelper helper = new GameHelper();
^
symbol: class GameHelper
location: class Game

Game.java:11: error: cannot find symbol
GameHelper helper = new GameHelper();
^
symbol: class GameHelper
location: class Game

Game.java:13: error: cannot find symbol
SimpleDotCom theDotCom = new SimpleDotCom();
^
symbol: class SimpleDotCom
location: class Game

Game.java:13: error: cannot find symbol
SimpleDotCom theDotCom = new SimpleDotCom();
^
symbol: class SimpleDotCom
location: class Game



I did comment out the import helper.GameHelper, and got these errors when I tried to recompile it into a .class.

package chap05;
//import helpers.GameHelper;
import java.util.Scanner;
public class Game {
public static void main (String[] args)
{
int numOfGuesses = 0;
GameHelper helper = new GameHelper();
SimpleDotCom theDotCom = new SimpleDotCom();
int randomNum = (int) (Math.random() * 5);
int[] locations = {randomNum, randomNum+1, randomNum+2};
theDotCom.setLocationCells(locations);
boolean isAlive = true;
while (isAlive == true)
{
String guess = helper.getUserInput("enter a number");
String result = theDotCom.checkYourself(guess);
numOfGuesses++;
if (result.equals("kill")) {
isAlive = false;
System.out.println("You took " + numOfGuesses + " guesses");
}
}
}
}

I also tried to work with chap05.Game.java, but that doesn't seem to do the trick, because I get the error it can't find the file, or it can not find or load the main class.

[Dave Tolls]

If you are in the directory that contains the chap05 directory then the compilation command should be:
javac chap05/Game.java

You use the file path, not dot notation.
That assumes you haven't set a CLASSPATH environment variable (which you shouldn't have done).

If you were in the chap05 directory then you would have to tell javac where the package root is:
javac -cp.. Game.java

That tells javac to use the directory above the one you are in as the classpath.