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Thread: Array Lists help!!

  1. #1
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    Default Array Lists help!!

    Hello everybody!

    I am new to java and i have a problem. I need to create an arraylist from the coordinates οφ the real and estimated values that I have read from a file.But i can't seem to do that! Can you help me please??


    I woul really appreciate your help cause i m lost!!!
    Last edited by lilika; January 6th, 2011 at 01:06 AM.


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    Default Re: Array Lists help!!

    sCurrentLine = s.readLine()) != null

    First off,

    sCurrentLine ==s.readLine()

    while ((sCurrentLine = s.readLine()) != null) {

    This line won't work.

    while((sCurrentLIne == s.readLine()) && (s.readLine() !=null)

    might work.

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    Default Re: Array Lists help!!

    mat = pat.matcher(sCurrentLine);

    sCurrentLine hasn't been initialized yet.

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    Default Re: Array Lists help!!

    // Print line as read from file
    System.out.println(sCurrentLine)

    Well, to just print out the lines alone read from the file without doing anything to them,

    well....you'd need to define the FileReader first before you do. But after that

    while (inFile.hasNext())
    {
    sCurrentLine = inFile.nextLine();
    System.out.prinltn(sCurrentLine);
    }

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    Default Re: Array Lists help!!

    int n = myArray.size();
    for (int i = 0; i < n; i++) {
    System.out.println(myArray.get(i));
    }

    You never added anything.

    Your size will be 0.

    You have to

    myArray.add(int index, Integer data);

  6. #6
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    Default Re: Array Lists help!!

    Quote Originally Posted by javapenguin View Post
    // Print line as read from file
    System.out.println(sCurrentLine)

    Well, to just print out the lines alone read from the file without doing anything to them,

    well....you'd need to define the FileReader first before you do. But after that

    while (inFile.hasNext())
    {
    sCurrentLine = inFile.nextLine();
    System.out.prinltn(sCurrentLine);
    }

    Yes i knew that but the problem was that i wanted to separate the numbers from the text and the symbols. That's where i messed up. I managed to do the first thing (read and seperate the integers) but i can't understand how to create the array list from the code i have...

    thank you for your answers but could you be a little more specific cause i m really new to java.

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    Default Re: Array Lists help!!

    Quote Originally Posted by javapenguin View Post
    int n = myArray.size();
    for (int i = 0; i < n; i++) {
    System.out.println(myArray.get(i));
    }

    You never added anything.

    Your size will be 0.

    You have to

    myArray.add(int index, Integer data);
    You are absolutely right but i dont know how to fill: myArray.add(int index, Integer data); with the integers i found when i read the file. Whta is my index and what is my data?

    Sorry for the stupid questions :-(

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    Default Re: Array Lists help!!

    Well, to separate the numbers and the text and symbols, maybe you could use a StringTokenizer.
    StringTokenizer (Java 2 Platform SE v1.4.2)

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    Default Re: Array Lists help!!

    Quote Originally Posted by lilika View Post
    You are absolutely right but i dont know how to fill: myArray.add(int index, Integer data); with the integers i found when i read the file. Whta is my index and what is my data?

    Sorry for the stupid questions :-(
    For starters, what exactly are you trying to add?

    Each number individually, each number as a pair, each number as a pair with reference to another pair?

    To add it, do something perhaps like this:

    StringTokenizer tokenizer = new StringTokenizer(sCurrentLine);

    String temp = tokenizer.nextToken();

    if (temp.equals("("))
    ignore Token and go on

    else if (temp.equals(")"))
    ignore Token and go on

    else if (temp.equals("->>>>>noise->>>>"))
    ignore Token and go on

    else if (temp.equals(","))
    ignore Token and go on

    else
    {

    Integer temp2 = Integer.parseInt(token);

    myArray.add(temp2);

    }

    Also, I'm sorry earlier. There are two possible add methods for ArrayList.

    add(E data) adds the data to the end of your ArrayList

    add(int index, E data) adds the data at the index index of your ArrayList.
    Last edited by javapenguin; January 3rd, 2011 at 02:58 PM.

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    Default Re: Array Lists help!!

    Quote Originally Posted by javapenguin View Post
    For starters, what exactly are you trying to add?

    Each number individually, each number as a pair, each number as a pair with reference to another pair?

    To add it, do something perhaps like this:

    StringTokenizer tokenizer = new StringTokenizer(sCurrentLine);

    String temp = tokenizer.nextToken();

    if (temp.equals("("))
    ignore Token and go on

    else if (temp.equals(")"))
    ignore Token and go on

    else if (temp.equals("->>>>>noise->>>>"))
    ignore Token and go on

    else if (temp.equals(","))
    ignore Token and go on

    else
    {

    Integer temp2 = Integer.parseInt(token);

    myArray.add(temp2);

    }

    Also, I'm sorry earlier. There are two possible add methods for ArrayList.

    add(E data) adds the data to the end of your ArrayList

    add(int index, E data) adds the data at the index index of your ArrayList.
    Thank you so much! I will try that and tell you about it! I am trying to add each number individually to an array list.I hope it will work!

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    Default Re: Array Lists help!!

    Quote Originally Posted by javapenguin
    while ((sCurrentLine = s.readLine()) != null) {

    This line won't work.
    Yes, it will work..

    To add values to an arraylist, just call the add function, not index is necessary when appending to the List

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    Default Re: Array Lists help!!

    I wrote it this way I don't know if I did it right, but there are errors on the lines with "ignore Token and go on;"

    Am I missing something???

    import java.io.BufferedReader;
    import java.io.FileReader;
    import java.io.IOException;
    import java.util.ArrayList;
    import java.util.StringTokenizer;
     
    public class Main {
     private static String token;
     
        public static void main(String[] args) throws IOException {
     
     String sCurrentLine;
    ArrayList<Integer> myArray = new ArrayList<Integer>();
     BufferedReader s = null;
     s = new BufferedReader(new FileReader("measurements.txt"));
     
    while ((sCurrentLine = s.readLine()) != null) {
     
    StringTokenizer tokenizer = new StringTokenizer(sCurrentLine);
     
    String temp = tokenizer.nextToken();
     
    if (temp.equals("(")){
    ignore Token and go on;
     
    } else if (temp.equals(")")){
    ignore Token and go on;
     
    }else if (temp.equals("->>>>>noise->>>>")){
    ignore Token and go on;
     
        }
        else{
     
                    }
       if (temp.equals(",")) {
    ignore Token and go on;
     
        }
        else
    {
     
    Integer temp2 = Integer.parseInt(token);
     
    myArray.add(temp2);
     
    }
            }
        }
        }

    The output is:

    Exception in thread "main" java.lang.NumberFormatException: null
    at java.lang.Integer.parseInt(Integer.java:417)
    at java.lang.Integer.parseInt(Integer.java:499)
    at xristina.Main.main(Main.java:45)
    Java Result: 1
    BUILD SUCCESSFUL (total time: 0 seconds)

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    Default Re: Array Lists help!!

    sCurrentLIne = s.readLine();

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    Default Re: Array Lists help!!

    import java.io.BufferedReader;
    import java.io.FileReader;
    import java.io.IOException;
    import java.util.ArrayList;
    import java.util.StringTokenizer;
     
    public class Main {
     private static String token;
     
        public static void main(String[] args) throws IOException {
     
     String sCurrentLine;
    ArrayList<Integer> myArray = new ArrayList<Integer>();
     BufferedReader s = null;
     s = new BufferedReader(new FileReader("measurements.txt"));
     
    while ((sCurrentLine = s.readLine()) != null) {
    sCurrentLine = s.readLine(); // you were missing this part
     
    StringTokenizer tokenizer = new StringTokenizer(sCurrentLine);
     
    String temp = tokenizer.nextToken();
     
    if (temp.equals("(")){
    ignore Token and go on;
     
    } else if (temp.equals(")")){
    ignore Token and go on;
     
    }else if (temp.equals("->>>>>noise->>>>")){
    ignore Token and go on;
     
        }
        else{
     
                    }
       if (temp.equals(",")) {
    ignore Token and go on;
     
        }
        else
    {
     
    Integer temp2 = Integer.parseInt(token);
     
    myArray.add(temp2);
     
    }
            }
        }
        }

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    Default Re: Array Lists help!!

    Also, you have an empty else.

  16. #16
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    Default Re: Array Lists help!!

    Yes i saw that and corrected it! It s late at night here!Sorry for that! But still the same errors in the "ignore Token and go on;" lines..

    package xristina;
     
    import java.io.BufferedReader;
    import java.io.FileReader;
    import java.io.IOException;
    import java.util.ArrayList;
    import java.util.StringTokenizer;
     
    public class Main {
     private static String token;
     
        public static void main(String[] args) throws IOException {
     
     String sCurrentLine;
    ArrayList<Integer> myArray = new ArrayList<Integer>();
     BufferedReader s = null;
     s = new BufferedReader(new FileReader("measurements.txt"));
     
    while ((sCurrentLine = s.readLine()) != null) {
    sCurrentLine = s.readLine(); // you were missing this part
     
    StringTokenizer tokenizer = new StringTokenizer(sCurrentLine);
     
    String temp = tokenizer.nextToken();
     
    if (temp.equals("(")){
    ignore Token and go on;
     
    } else if (temp.equals(")")){
    ignore Token and go on;
     
    }else if (temp.equals("->>>>>noise->>>>")){
    ignore Token and go on;
     
        }
        else{
     
     
       if (temp.equals(",")) {
    ignore Token and go on;
     
        }
        else
    {
     
    Integer temp2 = Integer.parseInt(token);
     
    myArray.add(temp2);
     
     }
     }
     }
     }
     }

    I don't mean to tire you. You are really helpfull. I must be doing something wrong but I m sure I ll Find it!

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    Default Re: Array Lists help!!

    What I meant by the psuedocode "Ignore token and go on" was to simply just do nothing with the token. Just add the ones that are ints.
    String temp;
    // I just fixed it to define temp before the while loop.  Otherwise, it'll be null and won't be defined till it hits the while loop, which it won't since it'll still be null.
     
    while (temp !=null)
    {
     temp = tokenizer.nextToken();
     
    if (temp.equals("(")){
    // don't add it.  Just go on
    }
     
    } else if (temp.equals(")")){
    // don't add it. Just go on.  
     
    }else if (temp.equals("->>>>>noise->>>>")){
    // don't add it. Just go on.
     
        }
        else{
     
     
       if (temp.equals(",")) {
    // don't add it. Just go on.
     
        }
        else
    {
     
    Integer temp2 = Integer.parseInt(temp);
     
    myArray.add(temp2);
     
     }
    }
    }
    Last edited by javapenguin; January 3rd, 2011 at 04:51 PM.

  18. #18
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    Default Re: Array Lists help!!

    Thank you so much. I managed to do that. Now that I made the array list, i have to loop throught it in order to calculate some averages. But i don't want the average of all the array list but from some specific numbers( which are in specific places)

    ex. A B C D E F G H I J K L ....

    I need the average of C+G+K+....+/ how many are they.
    Last edited by lilika; January 4th, 2011 at 10:00 AM.

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