Enter an integer:
12
The number 12 is positive
Good-bye for now

The Program as a Chart

Here is the program again, done as a flowchart. Because the answer to the question is "false", the false branch is performed. The "two-way split" of the program is easy to see in a two dimensional chart. It is harder to see this in a program where line follows line one after another.

import java.io.*;
class NumberTester
{
  public static void main (String[] args) 
      throws IOException
  {
     BufferedReader stdin = 
        new BufferedReader ( 
        new InputStreamReader( System.in ) );

    String inData;
    int    num;

    System.out.println("Enter an integer:");
    inData = stdin.readLine();
    num    = Integer.parseInt( inData );      

    if ( num < 0 )
      System.out.println("The number " + num + 
          " is negative"); 
    else
      System.out.println("The number " + num + 
          " is positive");  

    System.out.println("Good-bye for now");  
  }
}

The flow chart shows the overall logic of the program. Most of the details of syntax are left out. It is often helpful to sketch a flowchart when you are designing a program. You can use the flowchart to get the logic correct, then fill in the details when you write the program.