Only One Statement per Branch

The false block was not put inside braces:

if ( num < 0 )
    System.out.println("The number " + num + " is negative");   
else
    System.out.println("The number " + num + " is positive"); 
    System.out.print  ("positive numbers are greater ");   
    System.out.println("or equal to zero ");     
System.out.println("Good-bye for now");    

Our human-friendly indenting shows what we want, but the compiler will merely look for braces. It will see the equivalent of:

if ( num < 0 )
    System.out.println("The number " + num + " is negative");  // true-branch
else
    System.out.println("The number " + num + " is positive");  // false-branch
System.out.print  ("positive numbers are greater ");           // always executed  
System.out.println("or equal to zero ");                       // always executed
System.out.println("Good-bye for now");                        // always executed