Thread: simulate BufferedReader's readLine()

Any idea please? I am stuck, I look at BufferedReader methods but i didn't found any useful, need to do a method that return a String with the next line to read from a file. When it reach the end of file , it return null instead the String.

It is required that i pass BufferedReader as parameter

The only code I am able to think is "return br.readLine;" somewhere, but obviusly i need to remake that method, and not use it inside. I'm really stucked

import java.io.*;
 
public class leer {
 
	public static void main(String[] args) {
		try {
			BufferedReader br = new BufferedReader(new StringReader("First line\nSecond line"));
 
			leeLinea(br);
 
		}catch(FileNotFoundException e) {
 
		}catch(IOException e){
 
		}
	}
	static String leeLinea(BufferedReader br) throws IOException{
		String string = "";
		//while((string = nextLine()) != null)
			return string;
		return null;
	}
}

a

--- Update ---

Originally Posted by Norm

That is what the method is defined to do. What do you want your method to return when it finds end of file?

I'm not sure I understand your problem. null at end of file is easy to test for. Any code that reads data from a file needs a way to know when it has reached end of file. null says that there is no more data.

I must return null when it reach end of file.

I must write the code of readLine()

My method must pass a BufferedReader as parameter.
I can't use readLine() method defined by the API

he don't really say it, but it has no sense that i use readLine inside my method that simulates readLine

I don't think i should do this

static String leeLinea(BufferedReader br) throws IOException{
		String string = "";
		while((string = br.readLine()) != null)
			return string;
		return null;
}

"Need to do a method that return a String with the next line to read from a file. When it reach the end of file , it return null instead the String."



Should do this: without using readLine()

static String leeLinea(BufferedReader br) throws IOException{
		String string = "";
		while((string = br.readLine()) != null)
			return string;
		return null;
}

it's how i read a line from a file, but is just an example, how should my method work.
Anyway, if it is too hard, 100% sure i missunderstood my problem. so i ask tomorrow to my teacher. thank you for today

Ok, i know exactly what i have to do: I must simulate readLine() method, reading char by char, and returning the first String when find carriage return, and if it is the end of file, must return NULL.

I don't know how to check if a character is end of file. it doesn't work with ASCII: 3 (end of text)

in my while loop i get a infinite loop because i get an unknown character infinite.
My code:

import java.io.*;
 
public class Ejercicio13 {
 
	public static void main(String[] args) {
		try {
			BufferedReader br = new BufferedReader(new StringReader("En un lugar\r\nDe la mancha"));
 
 
			String linea = "";
			while((linea = leeLinea(br))!= null)
				System.out.println(linea);
		}catch(FileNotFoundException e) {
 
		}catch(IOException e){
 
		}
	}
	static String leeLinea(BufferedReader br) throws IOException{
		//Character caracter = null;
		char caracter = '\0';
		String linea = "";
 
		while((caracter = (char) br.read()) != 13){
			if(caracter == 3){
				return null;
			}
			linea+=caracter;
		}
		return linea;
	}
}

I did before, i see the char '?' then i search for char ? that is 63 and tried : if (caracter == (char)63) {return null;} but doesnt work. so i made this to find the ascii code for that char

for(int i=0; i<255; i++)
  if(caracter == (char) i)
     System.out.println(i);

but never show which ascii code is, so i don't know what to do

I even tried with i<5000 , and never show which one is

I think is an encoded byte or so...

it shows '-1' : System.out.println(br.read());

oh my god, now i understand what the -1 that uses the teacher means... thank you
this is like index -1 for string index right?

This is right?

if(caracter == (char)-1)

Looks like wrong

"The character read, as an integer in the range 0 to 65535 (0x00-0xffff), or -1 if the end of the stream has been reached"



Some help please. How to return the string when it find \n or when it find -1 but last index of string is not -1.

	//Character caracter = null;
		char caracter = '\0';
		String linea = "";
		int indice = 0;
		while((caracter = (char) br.read()) != 13 && caracter != (char)-1){
			indice++;
			linea+=caracter;
			if(linea.length()>0)
				if(linea.charAt(indice-1)!= (char)-1 && caracter == (char)-1)
					return linea;
		}
		if(caracter == 13)
			return linea;
 
		return null;

but then i could not return last string in my example input: new StringReader("En un lugar\r\nDe la mancha"))

i only return first line "en un lugar" but second one has append the -1 with the string, then i can't return the string, and at the same time after it return null

I tried many ways but this is the best. that doesn't show first character because i do a read() at start

	static String leeLinea(BufferedReader br) throws IOException{
		//Character caracter = null;
		char caracter = '\0';
		if((caracter = (char) br.read()) == (char)-1)
			return null;
		String linea = "";
		while((caracter = (char) br.read()) != 13 && caracter != (char)-1)
			linea+=caracter;
		return linea;
	}

They should make more methods for BufferedReader

I don't understand you at all. Do you mean this?

	static String leeLinea(BufferedReader br) throws IOException{
		char caracter = '\0';
		int esNulo = 0;
		if((esNulo = (int) br.read()) == -1)
			return null;
		String linea = "";
		while((caracter = (char) br.read()) != 13 && caracter != (char)-1)
			linea+=caracter;
		return linea;
	}

same problem ))

will check it tomorrow, thank u , good night