[RESOLVED] Java tutorial *help*

Here is my code I made by hand 100% so be nice if its riddled with unchecked exceptions.

Code:

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import java.io.FileReader;
import java.io.FileWriter;
import java.io.BufferedWriter;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.BufferedInputStream;
import java.io.Console;
import java.util.Arrays;
import java.io.IOException;
import java.io.DataOutputStream;
import java.io.DataInputStream;
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.EOFException;
import java.io.FileNotFoundException;



public class Test {
   
      public static boolean rightPlace() {
try {   
  BufferedReader br = new BufferedReader(new FileReader("Test2.txt"));
      if(br.readLine().equals("NewObjects")) {
            return true;
      } else { return false; }
      } catch(FileNotFoundException fnf) { System.err.println("fnf exception  " + fnf.getMessage());
} catch(IOException ioe) { System.err.println("error@:"+ ioe.getStackTrace());
}
 return false;
}

          public static void neoWriter(String data) {
BufferedWriter bw = null;
 try {     
    if(rightPlace() == true) {
          bw.newLine();
          bw.write(data);
      } else {    bw.newLine(); }
}  catch(IOException g) { System.err.println("ERR:" + g.getStackTrace() + "\n" + g.getMessage());
}
}
          public static void save(String data) {
        try { 
          BufferedWriter bw = new BufferedWriter(new FileWriter("Test2.txt"));
        neoWriter(data);
        bw.newLine();
        bw.flush();
    } catch(IOException e) { System.err.println("err:"+ e.getMessage());
}
  }

          public static void main(String[] args) {
         
String UInput;
        System.out.println("Type:");
    InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader bw = new BufferedReader(isr);
 
      try {
      UInput = bw.readLine();
      save(UInput);
}catch(IOException x) { System.err.println("err:"+ x.getStackTrace());
}
   
 


}}

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It compiles fine, it's just it doesn't well work when i run it, nothing happens? So clearly I made an overside but, where was it? I also, realize I could do a better job at exceptin handling, but I was just doing a simple test I wasn't sure if it was called for on a test. But, perhaps with some better exception handling (assuming it's not an unchecked exception) I might be able to find the cause, but by all means if you see a problem let me know please.

-Thanks for taking the time.

Please format your code, it makes it so much easier to read when blocks of code are aligned correctly.

Quote:

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It compiles fine, it's just it doesn't well work when i run it, nothing happens?

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Really, on my system I get the "Type:" prompt and I can enter some data.

It then falls over (throws a NullPointerException) because you are trying to read from the file before having written to it.

Oh duh my bad my compiler was set to a different file. Thanks keang I will format my code better form now on. I really would appricaite any other pointers you have. Like if my code is sloppy for any other reason. Also, I plan on switching out that if else statement with a for statement to loop through the file. Anyways Thanks again.

P.S: I have the file being read on my comp I have another program this will go into. I don't know if this is smart, but I tend to make my classes sepertaly test them then impliment them.

Quote:

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I really would appricaite any other pointers you have.

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It does seem overly complex but I don't know what you are trying to achieve so you may have a good reason for doing what you have done.

Code:

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    if(rightPlace() == true)

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It's considered bad practice to test if a boolean value equals true or false, you just need to do:

Code:

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    if( rightPlace() )

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Quote:

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P.S: I have the file being read on my comp I have another program this will go into. I don't know if this is smart, but I tend to make my classes sepertaly test them then impliment them.

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Sorry but I don't understand what you are trying to say.

Thanks I'll change that boolean. Also, I was trying to say that if I have a program I'm trying to create I'll usually test methods and, certain thigns on the side before implementing it. To work out the bugs on the side the when I put it into the real program I have most of the bugs worked out. It's just been easier that way for me.

Oh yea err. I have a nullpointerexception as well now. I'll try to fix it.

Quote:

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Originally Posted by keang

It then falls over (throws a NullPointerException) because you are trying to read from the file before having written to it.

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hmm.. Do you mean you have to write to a file to be able to read it? You cannot read an existing file? Maybe I should show the path.

Quote:

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Also, I was trying to say that if I have a program I'm trying to create I'll usually test methods and, certain thigns on the side before implementing it.

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Oh I see, in large projects or when solving complex problems this can be a useful approach to take but generally speaking you should be writing tests harnesses for your code using something JUnit. In which case you can write and test your code in-situ.

Quote:

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hmm.. Do you mean you have to write to a file to be able to read it?

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Yes, if you haven't written it yet how can you read from it?

Quote:

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Originally Posted by keang

Yes, if you haven't written it yet how can you read from it?

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What if the file already exists you just want to read it?

Your code looks like it should be able to read an existing file.
You need to be sure the file is where the program is looking for it to be.

It is in the exact same folder/path the class file, and run program is. The error confuses me, because usually if he document to be read is in the same file it doesn't reqire a directory. Any other suggestions?

But is that where the program is looking for it?
Create a File object for the file and print its absolutePath to see where the program is looking for the file.

Okay..

Quote:

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What if the file already exists you just want to read it?

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The file doesn't have any content at the point you are reading it, regardless of whether or nor it did when you ran the program as the first thing you do is create a FileWriter() which overwrites any existing file. If you want to append to an existing file you need to create a FileWriter using the 2 parameter constructor with the second parameter being 'true'.

The NullPointerException is not because the file doesn't exist, it's because the readline() method returns null when the end of the file is reached. You are calling the equals() returned of the returned value without checking to see if it is null.

New Code:

Code:

---

import java.io.FileReader;
import java.io.FileWriter;
import java.io.BufferedWriter;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.BufferedInputStream;
import java.io.Console;
import java.util.Arrays;
import java.io.IOException;
import java.io.DataOutputStream;
import java.io.DataInputStream;
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.EOFException;
import java.io.FileNotFoundException;
import java.nio.file.Files;
import java.io.BufferedInputStream;

public class Test {
   
      public static boolean rightPlace() {
try {   
  BufferedReader b7 = new BufferedReader(new FileReader("Test2.txt"));
      if(b7.readLine().equals("NewObjects")) {
            return true;
      } else { return false; }
      } catch(FileNotFoundException fnf) { System.err.println("fnf exception  " + fnf.getMessage());
} catch(IOException ioe) { System.err.println("error@:"+ ioe.getStackTrace());
    }
        return false;
  }

          public static void neoWriter(String data) {
 try  {     
  InputStream i7 = new BufferedInputStream(new FileInputStream("Test2.txt"));
  BufferedWriter bw = new BufferedWriter(new FileWriter("Test2.txt", true));
    if(rightPlace() == true) {
          bw.newLine();
          bw.write(data);
      } else if(i7.read() >= i7.available()) {
              System.err.println("Reached End of File");
        } else {    bw.newLine(); }
                                 
}  catch(IOException g) { System.err.println("ERR:" + g.getStackTrace() + "\n" + g.getMessage());
}
}
          public static void save(String data) {
        try { 
          BufferedWriter bw = new BufferedWriter(new FileWriter("Test2.txt", true));
        neoWriter(data);
        bw.newLine();
        bw.flush();
    } catch(IOException e) { System.err.println("err:"+ e.getMessage());
}
  }

          public static void main(String[] args) {
         
String UInput;
        System.out.println("Type:");
    InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader bw = new BufferedReader(isr);
 
      try {
      UInput = bw.readLine();
      save(UInput);
}catch(IOException x) { System.err.println("main method err:"+ x.getStackTrace());
}
   
 


}}

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Specific additoins include

Code:

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    InputStream i7 = new BufferedInputStream(new FileInputStream("Test2.txt"));

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and:

Code:

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} else if(i7.read() >= i7.available()) {
              System.err.println("Reached End of File");

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I still get null pointer exception thrown:

ERROR

Code:

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Type:
f
Exception in thread "main" java.lang.NullPointerException
        at Test.rightPlace(Test.java:28)
        at Test.neoWriter(Test.java:41)
        at Test.save(Test.java:54)
        at Test.main(Test.java:70)
Press any key to continue . . .

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Quote:

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java.lang.NullPointerException
at Test.rightPlace(Test.java:28)

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What variable is null on line 28? Backtrack in your code to find out why that variable does not have a valid value.

For example this code assumes that the world is perfect:
if(b7.readLine().equals("NewObjects")) {

You should read into a String variable first, check the contents of the String for null and then compare the contents

Quote:

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Originally Posted by Norm

You should read into a String variable first, check the contents of the String for null and then compare the contents

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I'm sorry I don't understand what you mean? Do you mean like a String literal, and then compare the String literal to the contents of the file?

Like:

Code:

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String check = "NewObject";
if(br.readLine.equals(check)) {// code }

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Read into a variable:
String theLine = br.readLine();

New and Improved:

Code:

---

import java.io.FileReader;
import java.io.FileWriter;
import java.io.BufferedWriter;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.BufferedInputStream;
import java.io.Console;
import java.util.Arrays;
import java.io.IOException;
import java.io.DataOutputStream;
import java.io.DataInputStream;
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.EOFException;
import java.io.FileNotFoundException;
import java.nio.file.Files;
import java.io.BufferedInputStream;

public class Test {
   
      public static boolean rightPlace() {
try {   
  String line;
  BufferedReader b7 = new BufferedReader(new FileReader("Test2.txt"));
  line = b7.readLine();
      if(line.equals("NewObjects")) {
            return true;
      } else { return false; }
      } catch(FileNotFoundException fnf) { System.err.println("fnf exception  " + fnf.getMessage());
} catch(IOException ioe) { System.err.println("error@:"+ ioe.getStackTrace());
    }
        return false;
  }

          public static void neoWriter(String data) {
 try  {     
  InputStream i7 = new BufferedInputStream(new FileInputStream("Test2.txt"));
  BufferedWriter bw = new BufferedWriter(new FileWriter("Test2.txt", true));
    if(rightPlace()) {
          bw.newLine();
          bw.write(data);
      } else if(i7.read() >= i7.available()) {
              System.err.println("Reached End of File");
        } else {    bw.newLine(); }
                                 
}  catch(IOException g) { System.err.println("ERR:" + g.getStackTrace() + "\n" + g.getMessage());
}
}
          public static void save(String data) {
        try { 
          BufferedWriter bw = new BufferedWriter(new FileWriter("Test2.txt", true));
        neoWriter(data);
        bw.newLine();
        bw.flush();
    } catch(IOException e) { System.err.println("err:"+ e.getMessage());
}
  }

          public static void main(String[] args) {
         
String UInput;
        System.out.println("Type:");
    InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader bw = new BufferedReader(isr);
 
      try {
      UInput = bw.readLine();
      save(UInput);
}catch(IOException x) { System.err.println("main method err:"+ x.getStackTrace());
}
   
 


}}

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I'd like to say before I continue I really appriciate your guy's help in making my code more legiable, and going through with me the proper syntax even if it isn't detrimental, but just to keep clean, and bug free code.

Anyways I still get this error

Code:

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Type:
Text I want implimented into the Text.txt
Exception in thread "main" java.lang.NullPointerException
        at Test.rightPlace(Test.java:30)
        at Test.neoWriter(Test.java:43)
        at Test.save(Test.java:56)
        at Test.main(Test.java:72)
Press any key to continue . . .

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Just so you don't think I'm lazy while I await one of your responses I am trying my best to track down why this runtime exception is being thrown. Keep in mind I plan on updating the exception handling as soon as I can track down ths error.

Thanks for taking the time.

java.lang.NullPointerException
at Test.rightPlace(Test.java:30)

You have seen this type of error before. YOU should know by now how to solve it. see post#15

Look at line 30 and see what variable has a null value. Then backtrack in your code to see why that variable does not have a valid value.

You forgot to do the second step in my earlier recommendation:
FIRST: You should read into a String variable first,
SECOND: check the contents of the String for null
THIRD: and then compare the contents

Okay thanks, and I'll try to pay more attention to what your saying. Here is what I got.

Code:

---

import java.io.FileReader;
import java.io.FileWriter;
import java.io.BufferedWriter;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.BufferedInputStream;
import java.io.Console;
import java.util.Arrays;
import java.io.IOException;
import java.io.DataOutputStream;
import java.io.DataInputStream;
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.EOFException;
import java.io.FileNotFoundException;
import java.nio.file.Files;
import java.io.BufferedInputStream;

public class Test {
   
      public static boolean rightPlace() {
try {   
  String line;
  BufferedReader b7 = new BufferedReader(new FileReader("Test2.txt"));
  line = b7.readLine();
      if(line != null && line.equals("NewObjects")) {
            return true;
      } else { return false; }
      } catch(FileNotFoundException fnf) { System.err.println("fnf exception  " +

fnf.getMessage());
} catch(IOException ioe) { System.err.println("error@:"+ ioe.getStackTrace());
    }
        return false;
  }

          public static void neoWriter(String data) {
 try  {     
  InputStream i7 = new BufferedInputStream(new FileInputStream("Test2.txt"));
  BufferedWriter bw = new BufferedWriter(new FileWriter("Test2.txt", true));
    if(rightPlace()) {
          bw.newLine();
          bw.write(data);
      } else if(i7.read() >= i7.available()) {
              System.err.println("Reached End of File");
      } else if(!rightPlace()) {
            bw.newLine();
              return;
  }
                                 
}  catch(IOException g) { System.err.println("ERR:" + g.getStackTrace() + "\n" +

g.getMessage());
    }
}
          public static void save(String data) {
        try { 
          BufferedWriter bw = new BufferedWriter(new FileWriter("Test2.txt", true));
        neoWriter(data);
        bw.newLine();
        bw.flush();
    } catch(IOException e) { System.err.println("err:"+ e.getMessage());
}
  }

          public static void main(String[] args) {
         
String UInput;
        System.out.println("Type:");
    InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader bw = new BufferedReader(isr);
 
      try {
      UInput = bw.readLine();
      save(UInput);
      return;
}catch(IOException x) { System.err.println("main method err:"+ x.getStackTrace());
}
   
 


}}

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It doesn't error at runtime it just does this

Code:

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Type:
What I want to write
Press any key to continue . . .

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Now it just does this, but does'nt write in the Test2.txt file.
I'll figure this one out for myself thanks though guy's you taught me a lot, just thought you deserved to know I fixed that error. Edit: we fixed that error ....more so you guys than me ; )