Thread: From txt file to array.

Hello there.

I have an assignmet where i have too make it so that i can read a txt file and turn it into an array and then print out the numbers.

I have numbers between 1 and 100, all random numbers, within a txt file.
The problem that i have atm is that i cannot print out anything from my arraylist.
I am doing something wrong but cannot tell what exactly, any ideas?

import java.io.BufferedReader;
import java.io.FileReader;
import java.util.ArrayList;
 
public interface Histrogram {
	// throws Exception is there to check if the file actually exists and if it
	// doesn't then it will tell us that by an error.
	public static void main(String[] args) throws Exception {
 
		// read();
 
	}
 
	static void read() throws Exception {
 
		ArrayList<Integer> list = new ArrayList<Integer>();
		// This method just reads a file.
 
		// The path that we want to read from.
		FileReader file = new FileReader("C:\\Users\\mrLowBot\\Desktop\\heltal.txt");
		// Reading it by BufferedReader.
		BufferedReader read = new BufferedReader(file);
		int[] data = new int[100];
		String text = "";
		int data1 = 0;
		int i = 0;
		// Actually reading it here.
		String line = read.readLine();
		while (line != null) {
			text += line;
			// line = read.readLine();
			data1 = Integer.valueOf(read.readLine());
			list.add(data1);
 
		}
		// System.out.println(text);
		System.out.println();
		for (int k : list) {
			System.out.println(k);
		}
	}
 
}

PS: Some code is under the "//" lines but that's only because i have tried to only print the numbers as they are and without trying to add them into an array and that worked fine.

Originally Posted by jim829

Did you see Norm's comment on your previous thread -> http://www.javaprogrammingforums.com...ere-begin.html

Regards,
Jim

Just saw it. Trying to do it in that way.

Originally Posted by Norm

Please explain what happens when you compile and execute the program.
If there are error messages, copy the full text and paste it here.

Well that's part of the problem because i don't even get any error messages.
So i get nothing from the console.

Hey again.

Been sick and been with family so have not been able to write any code.
But i now i have found the problem.

	static void read() throws Exception {
 
		ArrayList<Integer> list = new ArrayList<Integer>();
		// This method just reads a file.
 
		// The path that we want to read from.
		FileReader file = new FileReader("C:\\Users\\karwa\\Desktop\\heltal.txt");
		// Reading it by BufferedReader.
		BufferedReader read = new BufferedReader(file);
		int[] data = new int[100];
		String text = "";
		int data1 = 0;
		int i = 0;
		// Actually reading it here.
		String line = read.readLine();
		while (line != null) {
			text += line;
			// line = read.readLine();
			data1 = Integer.valueOf(read.readLine());
			list.add(data1);
 
		}
		// System.out.println(text);
		for (int k : list) {
			System.out.println(k);
		}
	}

This is the problem and i get an error from it

data1 = Integer.valueOf(read.readLine());

Any ideas? Thanks.

Originally Posted by Norm

Please copy the full text of the error message and paste it here. It has important info about the error.

Exception in thread "main" java.lang.NumberFormatException: For input string: " 55"
	at java.lang.NumberFormatException.forInputString(Unknown Source)
	at java.lang.Integer.parseInt(Unknown Source)
	at java.lang.Integer.valueOf(Unknown Source)
	at km222nb_lab4.Histrogram.read(Histrogram.java:36)
	at km222nb_lab4.Histrogram.main(Histrogram.java:14)

Originally Posted by Norm

That String has a leading space which is not a valid numeric digit. Use the String class's trim method to strip off leading/trailing spaces.

I see.
But, as usual, i get an error...

	                 String x = read.readLine();
			 data1 = Integer.valueOf(x.trim()); 
			 list.add(data1);

Error :

Exception in thread "main" java.lang.NullPointerException
	at km222nb_lab4.Histrogram.read(Histrogram.java:35)
	at km222nb_lab4.Histrogram.main(Histrogram.java:14)

Originally Posted by Norm

What variable has the null value? How did the variable get the null value?

public interface Histrogram {
	// throws Exception is there to check if the file actually exists and if it
	// doesn't then it will tell us that by an error.
	public static void main(String[] args) throws Exception {
 
		read();
 
	}
 
	static void read() throws Exception {
 
		ArrayList<Integer> list = new ArrayList<Integer>();
		// This method just reads a file.
 
		// The path that we want to read from.
		FileReader file = new FileReader("C:\\Users\\karwa\\Desktop\\heltal.txt");
		// Reading it by BufferedReader.
		BufferedReader read = new BufferedReader(file);
		String text = "";
		int data1 = 0;
		// Actually reading it here.
		String line = read.readLine();
		while (line != null) {
			text += line;
			// line = read.readLine();
			String x = read.readLine();
			data1 = Integer.valueOf(x.trim()); 
			list.add(data1);
 
		}
		// System.out.println(text);
		for (int k : list) {
			System.out.println(k);
		}
	}
 
}

Data1 has 0 but everything else does't have a value that is 0.

I see what you guys mean but i don't get any values back at all.
Rather stuck atm.

Originally Posted by jim829

Here is a contrived example that throws an npe. If you paste the code exactly as it exists here and then compile and run it, the stack trace of the npe should match the lines commented in the code.

import java.util.List;
 
public class TraceBackExample {
 
   List<Integer> list;
 
   public static void main(String[] args) {
	  new TraceBackExample().start(); // line 8
   }
 
   public void start() {
	  add(20, 30); // line 12
   }
 
   public void add(int a, int b) {
	  addSumToList(a + b); // line 16
   }
 
   public void addSumToList(int a) {
	  System.out.println(list + "  " + a);
	  list.add(a); // line 21
   }
 
}

Regards,
Jim

Originally Posted by Norm

What does that mean?
What is printed when you print the values of all the variables used on the line where the NPE happens?
Something must print if the statement is executed. Be sure to put the print statement before the statement where the NPE happens or it will not be executed.

Thanks guys, i think that i got it!

	static void read() throws Exception {
 
		ArrayList<Integer> list = new ArrayList<Integer>();
		// This method just reads a file.
 
		// The path that we want to read from.
		FileReader file = new FileReader("C:\\Users\\karwa\\Desktop\\heltal.txt");
		// Reading it by BufferedReader.
		BufferedReader read = new BufferedReader(file);
 
		String text = "";
		int data1 = 0;
 
		// Actually reading it here.
 
		String line;
		while ((line = read.readLine()) != null) {
			text += line;
			String g = read.readLine();
			data1 = Integer.valueOf(g.trim());
			list.add(data1);
 
		}
		System.out.println();
		for (int k : list) {
			System.out.println(k);
		}
		read.close();
	}

I believe that the problem was that "line" read null instantly and then nothing worked.
But by telling it to read from the while loop instead of outside of the while loop it got working.

I just dropped "line = read.readLine()" down one step into the while.

String line;
		while ((line = read.readLine()) != null)

--- Update ---

Yeah no nvm it is not working as it should be...

I still get null pointer exception when i try to print negative numbers or when there are more than one whole number at one
line such as "18 43" etc.
And i cannot print the first numbers from the first line.. they just show up a a blank space and then print the rest of the one after another.
Well we are only reading for each line so that should be ok. But negative numbers is something that i would like to have in the program but
without making it show an error.

Did you mean to read two lines of your text file per while loop? you do a read.readLine() twice for each loop

while ((line = read.readLine()) != null) {
	text += line;
	String g = read.readLine[();
	data1 = Integer.valueOf(g.trim());
	list.add(data1);
}

]

Originally Posted by tonya

Did you mean to read two lines of your text file per while loop? you do a read.readLine() twice for each loop

while ((line = read.readLine()) != null) {
	text += line;
	String g = read.readLine[();
	data1 = Integer.valueOf(g.trim());
	list.add(data1);
}

]

Yeah, i switched it to only use the trim to "line.trim()" and now i got all the numbers within my array.

Originally Posted by Norm

Work on one problem at a time

Please copy the full text of the error message and paste it here. It has important info about the error.

No need my friend. Works fine now. Seeing as how i am getting the numbers line per line and the fact is that
it doesn't include negative values but it won't matter in this case.

The next step is to somehow make a histogram out of the numbers within the array.

--- Update ---

So here i have a method that should be able to count numbers between 0 and 100 within the array that has 100 numbers from -50 to around 150.

This method does nothing other than to count to 100 and print the total. Which is 100..
But i want to see how many values there are from 0 to 100 within my array.

Any ideas? Tried to use the list.size() but that really doesn't give me what i want.

static void count() {
		int c = 0;
		for (int i = 1; i <= 100; i++) {
			c++;
		}
		System.out.println("Between the interval of [0, 100] there are : " + c);
                System.out.println("And the rest are : " +  150 - c); 
 
	}

Originally Posted by Norm

Use an if statement to detect the desired values
and a counter to count them.

Got it. Thanks