Question

I am a newbie and I really want to learn the concept instead of just copying and pasting code. I wanted to learn how exactly to use the Jave IO and was confused and disapointed to see so my different versions of code.

So I made my own notes and wanted to confirm with the experts here whether I got it right. these are just for my own reference. I know is not perfect but I would appreciate if you could confirm whether they are correct.

Use BufferedWriter and FileWriter to write a text file ( as characters). Disadvantage is you cannot write a primitive data type.

Ex:

BufferedWriter bw= new BufferedWriter (new FileWriter("a.txt", true)); 
String x;
while ((x=bw.readLine())!=null){
bw.newLine();
bw.write(x);
bw.flush();}

Use BufferedReader and FileReader to read a text file (as characters)

Ex:

BufferedReader br = new BufferedReader (new FileReader("b.txt")); 
String x;
while ((x=br.readLine())!=null){
System.out.println(x);}

Use DataOutputStream and FileOutputStream to write to a text file (in binary). Advantage is you can write primitive data types as well as strings.

Ex:

DataOutputStream dos = new DataOutputStream(new FileOutputStream("out.txt"));
dos.writeInt(cityIdA);    // int cityIdA = 9897;         
dos.writeUTF(cityNameA); //  String cityNameA = "Green Lake City";  
dos.writeInt(cityPopulationA); //   int cityPopulationA = 500000;  
dos.writeFloat(cityTempA); //  float cityTempA = 15.50f; 
dos.flush();

Use DataInputStream and FileInputStream to read a text file (in binary). Advantage is you can read primitive data types as well as strings.

Ex:

DataInputStream dis = new DataInputStream(new FileInputStream("inp.txt"));
int cityId1 =dis.readInt();    // int cityIdA = 9897;         
String cityName1 =dis.readUTF(); //  String cityNameA = "Green Lake City";  
int cityPopulation1 =dis.readInt(); //   int cityPopulationA = 500000;  
float cityTemperature1 =dis.readFloat(); //  float cityTempA = 15.50f; 

Actual code:

import java.io.*; 

class b{

public static void main (String args[]) throws IOException{
int cityIdA = 9897;         
String cityNameA = "Green Lake City"; 
int cityPopulationA = 500000;         
float cityTempA = 15.50f;      

BufferedWriter bw = new BufferedWriter(new FileWriter("shahar.txt"));

bw.write("9897");  
bw.write("Green Lake City"); 
bw.write("500000"); 
bw.write("15.50"); 
bw.flush();             
bw.close(); 

DataOutputStream dos = new DataOutputStream(new FileOutputStream("out.txt"));

dos.writeInt(cityIdA);      
dos.writeUTF(cityNameA);
dos.writeInt(cityPopulationA); 
dos.writeFloat(cityTempA);
dos.flush();

BufferedReader br = new BufferedReader (new FileReader("shahar.txt")); 
String x;
while ((x=br.readLine())!=null){
System.out.println(x);}


DataInputStream dos1 = new DataInputStream(new FileInputStream("out.txt"));
int cityId1 = dos1.readInt();    // int cityIdA = 9897;     
System.out.println( cityId1);
String cityName1 =dos1.readUTF(); //  String cityNameA = "Green Lake City";  
System.out.println(cityName1);
int cityPopulation1 =dos1.readInt(); //   int cityPopulationA = 500000;  
System.out.println(cityPopulation1);
float cityTemperature1 =dos1.readFloat(); //  float cityTempA = 15.50f; 
System.out.println(cityTemperature1);
 }
 }

Answer 1

Your code subjectively has stylistic issues. I’ll drop your examples here as though I wrote them myself.

Example 2

(I put this before example 1 for a reason)

BufferedReader br = new BufferedReader (new FileReader("b.txt")); 
String x;

while ((x = br.readLine()) != null)
{ // changed style, but otherwise fine
    System.out.println(x);
}

Example 1

// borrowed reader from example 1
BufferedReader br = new BufferedReader (new FileReader("b.txt")); 
BufferedWriter bw = new BufferedWriter (new FileWriter("a.txt", true)); 
String x;

// this part didn't work.  You were trying to read from a writer, as you write to it.
// if this were an object capable of reading and writing at the same time, you would
// run into issues because they wouldn't be rewinding after each operation and you'd
// end up with a combination of unexpected mirrored lines and garbled crap.

// changed loop to read from reader.  reads data from one file, line by line, and
// writes to another.
while ((x = br.readLine()) != null) 
{
    bw.write(x);  // in the other order, file will start with a blank line
    bw.newLine(); // in this order, file will end with one instead
}
bw.flush(); // its better if this is not in the loop

Example 3 and 4

Examples 3 and 4 are fine. You would use something like this if you needed to write lots of primitive types to a binary file. The other examples are much more suited for reading text.

Since you’re a newbie, I’ll give you some random advice too:

• Don’t blame a language for its shortcomings, learn to overcome them. (applies to all languages)
• Threads are not a solution to every problem. If you need more than one, write yourself a scheduler.
• There are often many ways to do the same thing, but often one is more right than the others.
• Don’t write code now that you will hate yourself for later.
• Which style you choose to use is irrelevant, but stick to it. That said, I don’t like yours. 🙂
• Whichever style you choose, make sure you can read it easily under all conditions.
• Your computer does not have infinite memory, don’t write code pretending that it does. The same goes for all other resources; nobody likes a glutton.