public class Test {

   public static void main(String[] args) {
      int a = 3;

      double b = a;

      System.out.println(b);
   }

}

3.0

public class Test1 {

   public static void main(String[] args) {
      double a = 3.0;

      int b = a;

      System.out.println(b);
   }

}

Test1.java:6: Incompatible type for declaration. Explicit cast needed to
convert double to int. 
      int b = a; 
          ^
1 error

public class Test2 {

   public static void main(String[] args) {
      int a = 1/3;

      double b = 1/3;

      System.out.println(a);
      System.out.println(b);
   }

}

0
0.0

public class Test3 {

   public static void main(String[] args) {
      int a = 1/3.0;

      System.out.println(a);
   }

}

Test3.java:4: Incompatible type for declaration. Explicit cast needed to
convert double to int. 
      int a = 1/3.0; 
          ^ 
1 error

import java.io.*;
import java.util.*;

public class Write {

// Since we are not going to create an instance of the class Write,
// in order to use a method we will use class methods so that
// we can call them from the main method.

   public static void change_string(int n) throws IOException {

// This methods accepts as input the number corresponding to the
// position we wish to change.

// In order to read from a file we must use the two classes
// FileReader and BufferedReader.

      FileReader file = new FileReader("Eratosthenes.data");
      BufferedReader inputFile = new BufferedReader(file);

// To get a line out of the file we use the readLine()
// method.

      String s = inputFile.readLine();

// Since we are done reading from the file we now close it.

      inputFile.close();

// We now break the string apart into tokens delimited by a ;.

      StringTokenizer myStringTokenizer = new StringTokenizer(s,";");

// We record the total number of tokens found in the string.

      int numberOfTokens = myStringTokenizer.countTokens();

// We are going to begin putting the tokens we find back together
// until we come to the token which we want to change. So we read
// the first token from the String and place that into a String
// called output.

      String output = myStringTokenizer.nextToken();

// Now we must decide which token we want to replace.

      while (myStringTokenizer.countTokens() > numberOfTokens-n+2)
         output += ";" + myStringTokenizer.nextToken();

      output += ";" + "n";

// We now read the token we replaced but don't record it.

      s = myStringTokenizer.nextToken();

// Now we go through the rest of the tokens and add them to the
// String output.

      while (myStringTokenizer.countTokens() > 0)
         output += ";" + myStringTokenizer.nextToken();

// Now we are ready to write the String back to the file so we
// again declare a FileWrite object and a PrintWriter object.	

      FileWriter file1 = new FileWriter("Eratosthenes.data");
      PrintWriter outputFile = new PrintWriter(file1);

// We write the string to the file.

      outputFile.println(output);

// We now close the file.

      outputFile.close();
   }

   public static void main(String[] args) throws IOException {

// In order to get input from the user we must use the InputStreamReader
// and BufferedReader classes.

      InputStreamReader stream = new InputStreamReader(System.in);
      BufferedReader keyboard = new BufferedReader(stream);

      System.out.println("Please enter n");

// We now use a wrapper class to turn the String that the user input
// into an int.

      int n = new Integer(keyboard.readLine()).intValue();

// Now we set up an output file and prepare it to be written to. We
// use the FileWriter and PrintWriter classes.

      FileWriter file = new FileWriter("Eratosthenes.data");
      PrintWriter outputFile = new PrintWriter(file);

// We initialize our output String with a beginning "y".

      String output = "y";

// Now we add in "y"s corresponding to all numbers up to n.

      for (int counter=3;counter<=n;counter++)
         output += ";" + "y";

// Now we write the String to our output file.

      outputFile.println(output);

// Now we close the output file.

      outputFile.close();

// We now set up two loops. The outer loop will go from 2 to the
// integer portion of the square root of n. The inner loop will
// go from counter+1 to n. If the counter variable in the inner
// for loop has a zero remainder when we divide it by the counter
// variable in the outer for loop, when we then change the string
// in the position corresponding to the counter variable in the inner
// loop in the String stored in Eratosthenes.data to an "n".

      for (int counter=2;counter<=(int)(Math.sqrt(n));counter++)
         for (int counter1=counter+1;counter1<=n;counter1++)
            if (counter1 % counter == 0)
               Write.change_string(counter1);

// Now that the string is set up, we read it from the file, and
// tokenize it. For each token we get to, if it is a "y" we report
// that the number corresponding to that position is a prime
// number. Otherwise we report that the number corresponding to
// that position is not a prime number.

      FileReader file1 = new FileReader("Eratosthenes.data");
      BufferedReader inputFile = new BufferedReader(file1);

      String s = inputFile.readLine();

      StringTokenizer myStringTokenizer = new StringTokenizer(s,";");

      int counter = 2;

      while (myStringTokenizer.countTokens() > 0)
         if (myStringTokenizer.nextToken().equals("y"))
            System.out.println(counter++ + " is prime.");
         else
            System.out.println(counter++ + " is not prime.");
   }

}