I'm stuck on this program I'm making for school. Here's my code:
public static void experiencePointFileWriter() throws IOException{
File writeFileResults = new File("User Highscore.txt");
BufferedWriter bw;
bw = new BufferedWriter(new FileWriter(writeFileResults, true));
bw.append(userName + ": " + experiencePoints);
bw.newLine();
bw.flush();
bw.close();
FileReader fileReader = new FileReader(writeFileResults);
char[] a = new char[50];
fileReader.read(a); // reads the content to the array
for (char c : a)
System.out.print(c); // prints the characters one by one
fileReader.close();
}
The dilemma I'm facing is how can I sort new scores with the scores in writeFileResults by the numerical value of int experiencePoints? If you're wondering about the variables userName is assigned by a textfield.getText method, and an event happens when you press one of 36 buttons which launches a math.Random statement with one of 24 possible outcomes. They all add different integer numbers to experiencePoints.
Well, I don't want to do your homework, and this does seem introductory so I'd like to give you some hints.
First, there's a few things missing:
We don't have some of the variables you've given us, so there is no type associated with oldScores
There is no reference to userName or experiencePoints outside this method call
If you can add this information, it would make this process easier. I could infer things, but then I might be wrong, or worse yet, have you learn nothing because I did your assignment for you. ;)
EDIT:
So, based on extra information, you're data file is holding an "array" of usernames and experience values. Thus, the best way (read: best design, not shortest) would be to load these into custom objects then write a comparator function (read: implement the abstract class Comparator).
Thus, in pseudo-Java, you'd have:
Declare your data type:
private static class UserScore {
private final String name;
private final double experience;
// ... fill in the rest, it's just a data struct
}
In your reader, when you read the values, split each line to get the values, and create a new List<UserScore> object which contains all of the values read from the file (I'll let you figure this part out)
After you have your list, you can use Collections#sort to sort the list to be the correct order, here would be an example of this:
// assuming we have our list, userList
Collections.sort(userList, new Comparator<UserScore>() {
public int compare(UserScore left, UserScore right) {
return (int)(left.getExperience() - right.getExperience()); // check the docs to see why this makes sense for the compare function
}
}
// userList is now sorted based on the experience points
Re-write your file, as you see fit. You now have a sorted list.
Related
I'm trying to get my ArrayList's index via indexOf. So far, I've got
My ArrayList: public static ArrayList<Shop> allShops = new ArrayList();
That what is supposed to get the index
Scanner editShop = new Scanner(System.in);
String shopToEdit = editShop.nextLine();
int i = allShops.indexOf(shopToEdit);
System.out.println(i); //see what our index is (returns -1 because the var doesn't seem to get the right input)
EditFunc.edit(i);
and this, that is supposed to change my arraylist
public static void edit(int index){
//change array with given input in edit
//TODO: Make it so they can choose what to edit
//with booleans if editTrueName = false and then later on make it true again
System.out.println("Enter the new shop name:");
Scanner editedShopAttribute = new Scanner(System.in);
String editedShopName = editedShopAttribute.nextLine();
System.out.println("Enter the new shop location:");
String editedShopLocation = editedShopAttribute.nextLine();
Shop EditedVar = new Shop();
EditedVar.createShop(editedShopName,editedShopLocation);
allShops.set(index, EditedVar);
}
I've copied the values that debugger showed me and replaced them with that, but it still doesn't seem to work. Am I taking in the wrong kind of data? What can I try?
If there's something that looks wrong with my code, I'm always up to try and make it better.
Can't you do it with a Map<String, Shop>? That way you could use the shopName as a key.
By the way, as I see your new with java and OOP, I strongly recommend you read Clean Code, by Robert C. Martin, its a game-changing book.
I don't believe you can make what you want work with an Array. The reason as pointed out in one of the comments is that you are looking for a String, but the Array contains Shop(s). Since a Shop contains more than just the ShopName, you will never be able to find it this way. You should use a "Map" for such purposes:
public static Map<String, Shop> allShopsMap = new HashMap<>();
If you add all the shops to this map, then when you get a ShopName as an input, you merely need to do:
Shop shopToEdit = allShopsMap.get(inputShopName);
then call the set methods on this object to alter name and location.
I have two files:
Grader.getFileInfo("data\\studentSubmissionA.txt");
Grader.teacherFiles("data\\TeacherListA.txt");
Both contain a list of math problems, but the TeacherList is unsolved in order to check that the StudentSubmission was not altered from the original version.
studentSubmission is sent to the Grader class and the method currently looks like this:
public static void getFileInfo(String fileName)
throws FileNotFoundException {
Scanner in = new Scanner(new File(fileName))
while (in.hasNext()) {
String fileContent = in.nextLine();
}
and the TeacherFiles method looks like
public static void teacherFiles(String teacherFiles)
throws FileNotFoundException{
Scanner in = new Scanner(new File(teacherFiles));
while (in.hasNext()){
String teacherContent = in.nextLine();
String line = teacherContent.substring(0, teacherContent.indexOf('='));
}
I don't know how to get these methods to another method in order to compare them since they're coming from a file and I have to put something in the method signature to pass them and it doesn't work.
I tried putting them in one method, but that was a bust as well.
I don't know where to go from here.
And unfortunately, I can't use try/catches or arrays.
Is it possible to send the .substring(0 , .indexof('=')) through the methods?
Like line = teacherFiles(teacherContent.substring(0 , .indexof('='))); Is it possible to do this?
Think in more general terms. Observe that your methods called getFileInfo and teacherFiles, respectively are the very same except a few nuances. So why do not we think about finding the optimal way of merging the two functionalities and handling the nuances outside of them?
It is logical that you cannot use arrays as you need to know the number of elements of your array before you initialize it and your array would have already been initialized when you read the file. So using an array for this task is either an overkill (for example you allocate 1000 elements in your memory and you use only 10 elements) or insufficient (if you create an array of 10 elements, but you would need 1000). So, due to the fact that you do not know the number of rows in advance you need to use another data structure for your task.
So create the following method:
public static AbstractList<String> readFile(String filePath) throws FileNotFoundException, IOException {
Scanner s = new Scanner(new File(filePath));
AbstractList<String> list = new ArrayList<String>();
while (s.hasNext()){
list.add(s.next());
}
s.close();
return list;
}
Then use the method to read the student file and to read the teacher file. Store the results into two separate AbstractList<String> variables, then iterate through them and compare them as you like. Again, think in more general terms.
I have a CSV file which has only one column with 100+ rows. I would like to put those values in an one dimensional array(only if its possible). So that it works as same as if I wrote a string array manually. I.e.
String[] username = {'lalala', 'tatata', 'mamama'}; //<---if I did it manually
String[] username = {after passing the CSV values}; //<---I want this like the above ones.
Then later I would like to be able to initialized that class to a different class, say if the class that holds the array is called ArrayClass, I would like to be able to initialized this to different class, like this --
public class MainClass{
ArrayClass array = new ArrayClass();
//Then I would like to be able to do this
someMethod(array.username);
}
I know I asked a lot of things but I seriously appreciate all your help. Even if you see this question and say THIS IS BS. Oh and one more thing I would prefer it to be in JAVA.
It might be easier to use an arraylist rather than an array as you dont have to worry about number of rows. An array has a fixed size that cant be changed. i.e ArrayList
As you have only one column you will not need to worry about commas in csv
Example code would look something like this:
import java.util.*;
import java.io.*;
public class MyClass {
private ArrayList<String> MyArray = new ArrayList<String>();
private Scanner scan;
public MyClass(){
try {
scan = new Scanner(new File("MyFile.csv"));
} catch (IOException ioex) {
System.out.println("File Not Found");
}
}
public ArrayList<String> getArray() {
while (scan.hasNext()) {
Scanner line = new Scanner(scan.nextLine());
MyArray.add(line.next());
}
return MyArray;
}
}
And in the main:
MyClass f = new MyClass();
System.out.println(f.getArray());
If it's just a csv you can use the split method of string with a proper regex.
Please do check the split method
The first half of your question is easy and can be handled in a number of different ways. Personally, I would use the Scanner class and set the delimiter to be ",". Create a new Scanner Object and then call setDelimiter(",") on it. Then simply scan through the tokens. See the example on the documentation. This method of doing things is effective because it handles reading in the file and separating it based on your criteria (the ',' character).
I am trying to read info from a file and create objects out of that information. Every 6 or so lines of the file is a different unit, meaning that the first set of lines are relevant to object A, the next set to object B, and so on.
I can read from the file and create my object just fine--for the first set. My problem is that I don't know how to get the reader to pick up from the spot it left off at when creating the next object...
(Note: the read() method which creates the file is part of the new object being created, not in a main() or anything like that). Here are the relevant bits of code:
The driver:
public class CSD{
public static void main (String[] argv){
Vector V=new Vector(10);
CoS jon=new CoS();
jon.display();
}//end main
}
which calls CoS, whose constructor is:
public CoS(){
try{
String fileName=getFileName();
FileReader freader=new FileReader(fileName);
BufferedReader inputFile=new BufferedReader(freader);
this.read(inputFile);
setDegree(major);
setStatus(credits);
} catch(FileNotFoundException ex){
}//end catch
}
Which calls both read() and getFileName():
public void read(BufferedReader inputFile){
try{
int n;
super.read(inputFile);
String str=inputFile.readLine();
if (str!=null){
n=Integer.parseInt(str);
setCredits(n);
str=inputFile.readLine();
setMajor(str);
}//end if
}catch(IOException ex){}
}//end method
public String getFileName() {
Scanner scan = new Scanner(System.in);
String filename;
System.out.print("Enter the file name and path ==> ");
filename = scan.nextLine();
System.out.println("");
return filename;
}
Thanks in advance, guys!
Why not use ObjectInputStream and ObjectOutputStream? Or any kind of real serialization?
javadoc: http://docs.oracle.com/javase/6/docs/api/java/io/ObjectOutputStream.html
example code: http://www.javadb.com/writing-objects-to-file-with-objectoutputstream
Basically, since you write your objects to a file and want to take care of the lines where they are located, I'll suggest a few other serialization alternatives.
One is the Object * Stream - you create a ObjectStream on a File and just write objects thru it. Later when you read, you read the objects in the reverse order you wrote them and they will come back just as you wrote them.
Another is to implement Serializable. Remember that transient keyword? Use it on fields you do not want to save to the file.
And then there's the raw "by hand" approach where you save only the things you want to save and reconstruct the objects later by passing these initialization values to their constructor. Kinda like people suggested that you make the file line a argument to the ctor :)
EDIT:
guess writing with Object*Streams requires you to implement Serializable or Externalizable.
but if the example code isn't clear enough, ask :)
Here's the situation :
I have 3 objects all named **List and I have a method with a String parameter;
gameList = new StringBuffer();
appsList = new StringBuffer();
movieList = new StringBuffer();
public void fetchData(String category) {
URL url = null;
BufferedReader input;
gameList.delete(0, gameList.length());
Is there a way to do something like the following :
public void fetchData(String category) {
URL url = null;
BufferedReader input;
"category"List.delete(0, gameList.length());
, so I can choose which of the lists to be used based on the String parameter?
I suggest you create a HashMap<String, StringBuffer> and use that:
map = new HashMap<String, StringBuffer>();
map.put("game", new StringBuffer());
map.put("apps", new StringBuffer());
map.put("movie", new StringBuffer());
...
public void fetchData(String category) {
StringBuffer buffer = map.get(category);
if (buffer == null) {
// No such category. Throw an exception?
} else {
// Do whatever you need to
}
}
If the lists are fields of your object - yes, using reflection:
Field field = getClass().getDeclaredField(category + "List");
List result = field.get();
But generally you should avoid reflection. And if your objects are fixed - i.e. they don't change, simply use an if-clause.
The logically simplest way taking your question as given would just be:
StringBuffer which;
if (category.equals("game"))
which=gameList;
else if (category.equals("apps"))
which=appList;
else if (category.equals("movie"))
which=movieList;
else
... some kind of error handling ...
which.delete();
As Jon Skeet noted, if the list is big or dynamic you probably want to use a map rather than an if/else/if.
That said, I'd encourage you to use integer constant or an enum rather than a String. Like:
enum ListType {GAME, APP, MOVIE};
void deleteList(ListType category)
{
if (category==GAME)
... etc ...
In this simple example, if this is all you'd ever do with it, it wouldn't matter much. But I'm working on a system now that uses String tokens for this sort of thing all over the place, and it creates a lot of problems.
Suppose you call the function and by mistake you pass in "app" instead of "apps", or "Game" instead of "game". Or maybe you're thinking you added handling for "song" yesterday but in fact you went to lunch instead. This will successfully compile, and you won't have any clue that there's a problem until run-time. If the program does not throw an error on an invalid value but instead takes some default action, you could have a bug that's difficult to track down. But with an enum, if you mis-spell the name or try to use one that isn't defined, the compiler will immediately alert you to the error.
Suppose that some functions take special action for some of these options but not others. Like you find yourself writing
if (category.equals("app"))
getSpaceRequirements();
and that sort of thing. Then someone reading the program sees a reference to "app" here, a reference to "game" 20 lines later, etc. It could be difficult to determine what all the possible values are. Any given function might not explicitly reference them all. But with an enum, they're all neatly in one place.
You could use a switch statement
StringBuffer buffer = null;
switch (category) {
case "game": buffer = gameList;
case "apps": buffer = appsList;
case "movie": buffer = movieList;
default: return;
}