I'm trying to wrap my head around a problem I have in a programming set.
We're supposed to write code that reads from a file and prints it out. I get that, I can do it.
What he wants us to do is have it print out in reverse.
the file reads:
abc
123
987
He wants:
987
123
abc
The code, as it is, is as follows:
{
FileReader n=new FileReader("F:\\Java\\Set 8\\output1.txt");
Scanner in=new Scanner(n);
int l;
while (in.hasNext())
{
l=in.nextInt();
System.out.println(l);
}
in.close();
}
}
Yes, I am using java.io.*; and Scanner.
What would be the simplest way to do this?
EDIT EDIT EDIT
Here's the improved code, where I try to put it into an array.
The data in the array isn't printing out.
public static void main(String[] args) throws IOException
{
int[]Num=new int[20];
Scanner in=new Scanner(new FileReader("F:\\Java\\Set 8\\output1.txt"));
int k;
for (k=0;k<20;k++)
{
Num[k]=in.nextInt();
}
//in.close();
for (k=20;k<20;k--)
{
System.out.print(+Num[k]);
}
//in.close();
}
The most simplest way is to construct a List and add each line to the list while reading from the file. Once done, print the list items in reverse.
Here is my version of code for your problem.
public static void main(String[] args) throws FileNotFoundException {
FileReader n = new FileReader("/Users/sharish/Data/abc.xml");
Scanner in = new Scanner(n);
ArrayList<String> lines = new ArrayList<String>();
while (in.hasNext()) {
lines.add(in.nextLine());
}
in.close();
for (int i = lines.size() - 1; i >= 0; i--) {
System.out.println(lines.get(i));
}
}
Use Stack.
public static void displayReverse() throws FileNotFoundException {
FileReader n=new FileReader("C:\\Users\\User\\Documents\\file.txt");
Scanner in=new Scanner(n);
Stack<String> st = new Stack<String>();
while (in.hasNext()) {
st.push(in.nextLine());
}
in.close();
while(!st.isEmpty()) {
System.out.println(st.pop());
}
}
If you are permitted the use of third party APIs, Apache Commons IO contains a class, ReversedLinesFileReader, that reads files similar to a BufferedReader (except last line first). Here is the API documentation: http://commons.apache.org/proper/commons-io/apidocs/org/apache/commons/io/input/ReversedLinesFileReader.html
Another (less efficient) solution is hinted at in the comments. You can read your entire file into an ArrayList, reverse that list (e.g. by pushing its contents onto a stack and then popping it off), and then iterate through your reversed list to print.
EDIT:
Here is a crude example:
ArrayList<String> lines = new ArrayList<String>();
Scanner in = new Scanner(new FileReader("input.txt"));
while (in.hasNextLine())
{
lines.add(in.nextLine());
}
Use an ArrayList instead of a static array. We don't necessarily know the length of the file in advance so a static array doesn't make sense here. http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html
Your example input 123, abc, etc, contains characters as well as ints, so your calls to hasNextInt and nextInt will eventually throw an Exception. To read lines use hasNextLine and nextLine instead. These methods return String and so our ArrayList also needs to store String. http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html#hasNextLine()
Once the file is in a list (not a good solution if the file is large - we've read the entire file into memory) we can either reverse the list (if keeping a reversed form around makes sense), or just iterate through it backwards.
for (int i=lines.size()-1; i>=0; i--) // from n-1 downTo 0
{
String line = lines.get(i);
System.out.println( line );
}
public static void main(String[] args) throws Exception{
String fileName = "F:\\Java\\Set 8\\output1.txt";
RandomAccessFile raf = new RandomAccessFile(fileName,"r");
int len = (int) raf.length();
raf.seek(len);
while(len >= 0){
if(len == 0){
raf.seek(0);
System.out.println(raf.readLine());
break;
}
raf.seek(len--);
char ch = (char)raf.read();
if(ch == '\n'){
String str = raf.readLine();
System.out.println(str);
}
}
}
try using org.apache.commons.io.input.ReversedLinesFileReader, it should do what you want.
You could read the lines like you are already doing, but instead of printing them (because that would print them in order and you need it the other way around), add them to some memory structure like a List or a Stack, and then, in a second loop, iterate this structure to print the lines in the needed order.
Using your code and the answers in the comments, here's an example of how you would store the strings into the arraylist and then print them out in reverse (building off of your own code)
{
FileReader n=new FileReader("F:\\Java\\Set 8\\output1.txt");
Scanner in=new Scanner(n);
int l;
ArrayList<String> reversed = new ArrayList<String>(); // creating a new String arraylist
while (in.hasNext())
{
l=in.nextInt();
System.out.println(l);
reversed.add(l); // storing the strings into the reversed arraylist
}
in.close();
// for loop to print out the arraylist in reversed order
for (int i = reversed.size() - 1; i >= 0; i--) {
System.out.println(reversed.get(i));
}
}
}
Using Java 8:
try(PrintWriter out =
new PrintWriter(Files.newBufferedWriter(Paths.get("out.txt")))) {
Files.lines(Paths.get("in.txt"))
.collect(Collectors.toCollection(LinkedList::new))
.descendingIterator()
.forEachRemaining(out::println);
}
Related
This is a project from school, but i'm only asking for help in the logic on one small part of it. I got most of it figured out.
I'm being given a file with lines of string integers, for example:
1234 123
12 153 23
1234
I am to read each line, compute the sum, and then go to the next one to produce this:
1357
188
1234
I'm stuck on the scanner part.
public static void doTheThing(Scanner input) {
int[] result = new int[MAX_DIGITS];
while(input.hasNextLine()) {
String line = input.nextLine();
Scanner linesc = new Scanner(line);
while(linesc.hasNext()) {
String currentLine = linesc.next();
int[] currentArray = convertArray(stringToArray(currentLine));
result = addInt(result, currentArray);
}
result = new int[MAX_DIGITS];
}
}
In a nutshell, I want to grab each big integer, put it an array of numbers, add them, and then i'll do the rest later.
What this is doing it's basically reading all the lines and adding everything and putting it into a single array.
What i'm stuck on is how do I read each line, add, reset the value to 0, and then read the next line? I've been at this for hours and i'm mind stumped.
Edit 01: I realize now that I should be using another scanner to read each line, but now i'm getting an error that looks like an infinite loop?
Edit 02: Ok, so after more hints and advice, I'm past that error, but now it's doing exactly what the original problem is.
Final Edit: Heh....fixed it. I was forgetting to reset the value to "0" before printing each value. So it makes sense that it was adding all of the values.
Yay....coding is fun....
hasNext method of the Scanner class can be used to check if there is any data available in stream or not. Accordingly, next method used to retrieve next continuous sequence of characters without white space characters. Here use of the hasNext method as condition of if doesn't make any sense as what you want is to check if the there are any numerical data left in the current line. You can use next(String pattern).
In addition, you can try this solution even though it is not optimal solution...
// In a loop
String line = input.nextLine(); //return entire line & descard newline character.
String naw[] = line.split(" "); //split line into sub strings.
/*naw contains numbers of the current line in form of string array.
Now you can perfom your logic after converting string to int.*/
I would also like to mention that it can easily & efficiently be done using java-8 streams.
An easier approach would be to abandon the Scanner altogether, let java.nio.io.Files to the reading for you and then just handle each line:
Files.lines(Paths.get("/path/to/my/file.txt"))
.map(s -> Arrays.stream(s.split("\\s+")).mapToInt(Integer::parseInt).sum())
.forEach(System.out::println);
If i were you i would be using the BufferedReader insted of the Scanner like this:
BufferedReader br = new BufferedReader(new FileReader("path"));
String line = "";
while((line = br.readLine()) != null)
{
int sum = 0;
String[] arr = line.split(" ");
for(String num : arr)
{
sum += Integer.parseInt(num);
}
System.out.println(sum);
}
Considering the level you're on, I think you should consider this solution. By using only the scanner, you can split the lines into an array of tokens, then iterate and sum the tokens by parsing them and validating that they're not empty.
import java.util.*;
class SumLines {
public static void main(String[] args) {
Scanner S = new Scanner(System.in);
while(S.hasNext()) {
String[] tokens = S.nextLine().split(" ");
int sum = 0;
for(int i = 0; i < tokens.length; i++) {
if(!tokens[i].equals("")) sum += Integer.parseInt(tokens[i]);
}
System.out.println(sum);
}
}
}
I am a beginner in programming. I am currently learning how to convert texts from notepad into array line by line. An instance of the text in notepad,
I am a high school student
I love banana and chicken
I have 2 dogs and 3 cats
and so on..
In this case, the array[1] will be string 'I love banana and chicken'.
The lines in the notepad can be updated and I want the array to be dynamic/flexible. I have tried to use scanner to identify each of the lines and tried to transfer them to array. Please refer to my code:
import java.util.*;
import java.io.*;
import java.util.Scanner;
class Test
{
public static void main(String[] args)
throws Exception
{
File file = new File("notepad.txt");
Scanner scanner = new Scanner(file);
String line;
int i = 0;
int j = 0;
while (scanner.hasNextLine()) {
i++;
}
String[] stringArray = new String[i];
while (scanner.hasNextLine()) {
line = scanner.nextLine();
stringArray[j] = line;
j++;
}
System.out.println(stringArray[2]);
scanner.close();
}
}
I am not sure why there is runtime-error and I tried another approach but still did not produce the result that I want.
The first loop would be infinite because you check if the scanner has a next line, but never advance its position. Although using a Scanner is fine, it seems like a lot of work, and you could just let Java's nio package do the heavy lifting for you:
String[] lines = Files.lines(Paths.get("notepad.txt")).toArray(String[]::new);
You can simply do it by creating an ArrayList and then converting it to the String Array.
Here is a sample code to get you started:
public static void main(String[] args) throws FileNotFoundException {
Scanner in = new Scanner(new File("notepad.txt"));
List<String> outputList = new ArrayList<>();
String input = null;
while (in.hasNextLine() && null != (input = in.nextLine())) {
outputList.add(input);
}
String[] outputArray = new String[outputList.size()];
outputArray = outputList.toArray(outputArray);
in.close();
}
Since you want array to be dynamic/flexible, I would suggest to use List in such case. One way of doing this -
List<String> fileLines = Files.readAllLines(Paths.get("notepad.txt"));
I am working on a class assignment where we can only use arrays and no Collection classes to read a text file and fill an array with information from the text file. the file ArrayData.txt is the information bellow.
The file is formatted in this way:
3 //First line states how many sets are in the file
2 //Next line:there are x numbers in the set
10.22 567.98 //Next Line states the doubles that are in the set
//The pattern continues from there
1 // x numbers in the next set
20.55 // Double in the set
3
20.55 2.34 100.97
My issue is filling the initial array with an array, then filling the second array with the doubles.
Essentially, I want it to look like this:
initArray[0]=> smallArray[2]={10.22,5.67.98}
initArray[1]=> smallArray[1]={20.55}
initArray[2]=> smallArray[3]={20.55,2.34,100.97}
Here is what I have so far:
public static double[] largeArray;
public static double[] insideArray;
public static void main(String[] args) {
String fileInputName = "ArrayData.txt";
Scanner sc = null;
try {
sc = new Scanner(new BufferedReader(new FileReader(fileInputName)));
while (sc.hasNextLine()) {
int i = sc.nextInt();
largeArray= new double[i];
for(int x=0; x<i;x++)
{
int z = sc.nextInt();
insideArray= new double[z];
for(int y=0; y<z; y++)
{
insideArray[z]=sc.nextDouble();
}
}
}
}
catch (FileNotFoundException e) {
e.printStackTrace();
}
finally {
if (sc != null)
sc.close();
}
}
First off, does this logic even make sense? Secondly, I keep getting an array out of bounds error, so I know something is right, I'm just not sure where.
Remove the while. You want the body to execute only once. Line breaks at the end of the file may cause it to run again and then there will be no nextInt(). If you want to support empty files, make it an if.
Secondly, insideArray[z] = ... should be insideArray[y] = ...
Finally, largeArray should be an array of arrays double[][] (a so called jagged array) and you want to assign insideArray to the according place after filling it.
to clarify: the code below logs data from the file reader into an array. In this situation I must know the number of lines (ex 11). I want to use an array list instead of an array so that Im not forced to predefine the # of indices.
import java.io.*;
public class ReadMyFile {
public static void main(String[] args) throws FileNotFoundException, IOException {
FileReader reader = new FileReader("data.txt");
System.out.println("We have made a FileReader");
char [] data = new char[11];
reader.read(data);
for (int i = 0; i < data.length; i++) {
System.out.print(data[i]);
}
reader.close();
}
}
You can use read() method instead of read(some_array) like that:
List<Character> charList = new ArrayList<>()
char c;
while ((c = reader.read()) != -1) {
charList.add(c);
}
read() reads one character so you can create a loop and read characters one by one and after reading every character you can add that character to a list. When there are no more characters to read read() returns -1 and that terminates a loop.
I'm want to read in from a file and then split it into separate parts and then access it and print it out. I know i can't do it the way it looks now. Please reply asap. The object of the program is to read in from a file points where i split it into x and y values, then sort these values according to there polar_order(this i have figured out) i just want to print out the values for testing.
Thanks
public static void main(String[] args){
int count = 0;
Scanner read = new Scanner(System.in);
int N = read.nextInt();
while(read.hasNext()){
String nN = read.nextLine();
String[]cord = nN.split(" ");
int x = Integer.parseInt(args[0]);
int y = Integer.parseInt(args[1]);
count++;
}
read.close();
for(int i = 0; i<N;i++){
System.out.print(x[i]);
}
Hope you are trying to print the contents of the string array 'cord'.
Try this code:
string dataToPrint = string.Join(" ", cord);
Not sure how you've structured your file but if you want to read in a file, here's an indication of how you might do that. Replace the while method with the method you need to extract the x, y values... you should probably apply Nist's answer to do so (use an ArrayList).
try {
Scanner s = new Scanner(new File("your file path"));
while (s.hasNextLine()) {
System.out.println(s.nextLine());
}
s.close();
}
catch (Exception e) {
System.out.println(e.getMessage());
}
I've found the easiest way to print the contents of an array (assuming it's not null) is this:
System.out.println(Arrays.toString(array));
For some odd reason, most of the list classes give nice output:
[1, 2, 3]
whereas arrays gives you a type/address indicator:
[Ljava.lang.String;#10b62c9
I've never quite understood why they didn't do something so that arrays had nicer output without having to call some utility function.