FAQ: Input and Output: Lesson - FileInputStream

This community-built FAQ covers the “FileInputStream” exercise from the lesson “Input and Output: Lesson”.

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This exercise can be found in the following Codecademy content:

Learn Intermediate Java

FAQs on the exercise FileInputStream

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I assume that this sets i to be the next integer read from the file, and then checks whether that integer is not -1.

    while((i = inputFile.read()) != -1) {    
      System.out.print((char)i);
      j++; 
    }

which would be the same as doing:

    i = inputFile.read();
    while(i != -1) {
      System.out.print((char)i);
      i = inputFile.read();
    }

How would I read to contents of a file into a string?

The best I could do was:

    FileInputStream inStream = new FileInputStream(path);
    int i = 0;
    int j = 0;
    
    // get length first
    while((i = inStream.read()) != -1) {    
      j++; 
    }
    inStream.close();
    //j++;
    // j is the length
    
    // make an array of chars
    char[] charray = new char[j];
    FileInputStream inStream2 = new FileInputStream(path);
    for (int k = 0; k < j; k++) {
      i = inStream2.read();
      charray[k] = (char)i;  // error? since i can be negative?
    }
    inStream2.close();
    // make the array into a string
    String str = new String(charray);

I guess the assumption is that characters are encoded as one byte in the text file (UTF-8 or ASCII or something like that).

EDIT: I found a constructor for strings that uses bytes, so I guess its better to use that here.

modified code
    FileInputStream inStream = new FileInputStream(path);
    int i = 0;
    int j = 0;
    
    // get length first
    while((i = inStream.read()) != -1) {    
      j++; 
    }
    inStream.close(); 
    // j is the length
    
    // make an array of bytes
    byte[] bytes = new byte[j];
    FileInputStream inStream2 = new FileInputStream(path);
    for (int k = 0; k < j; k++) {
      i = inStream2.read();
      bytes[k] = (byte)i; // warning?
      // conversion warning because bytes use less space than ints?
    }
    inStream2.close();
    // make the array into a string
    String str = new String(bytes);

The task includes “throwing an IOException”, but Codecademy had never taught me how to do it or what it is in the first place (either in Learn Java or previous steps of Learn Intermediate Java)

1 Like

I’m disappointed that this part wasn’t clearly explained. Why should it be (not) equal to -1? What is (char), exactly? Not the datatype itself, but putting it in front of a variable in parentheses

int i = 0;
// A loop to access each character
while((i = inputFile.read()) != -1) {
// Printing each character as it’s reached
System.out.print((char)i);

(char) x would cast variable x as a char, meaning it would try to get the char version of what’s in x.

1 Like

I would appreciate if Codecademy told me about it in some degree of detail (at least, at some point). I don’t even know how to google it: I don’t know what this practice is called! :anguished: