Need help verifying positive numbers

Question

I have a payroll program I've been working on for class the last few weeks. The most recent modification is that I need to confirm the hours and pay scale are entered in positive numbers. I've tried a while and an if...else statement and am getting an error telling me that I have an "illegal start" to the expression, and that the way I've written the statement is incompatible with boolean. Here is the code - I've colored the if...else statements red. The else statements don't give me an error, but the if statements do. (BTW, I've had the same problem trying to use a while statement.)
I'm pretty sure it has something to do with how I've written the if statement, but I can't put my finger on it. Can someone help?
Thanks,
import java.util.Scanner; // program uses Scanner
public class WeeklyPayrollTest
      public static void main(String args[])
        // create scanner to obtain input from command window
        Scanner input = new Scanner( System.in );
        // declare variables
        String exitPayroll;
        exitPayroll = "N";
        double numberHours = 0;
        double payRate = 0;
        // create a WeeklyPayroll object and assign it to currentPayroll
        WeeklyPayroll currentPayroll = new WeeklyPayroll();
        PayScale thisPay = new PayScale();
        while( exitPayroll.equalsIgnoreCase( "N" ) ) // begin while loop
              // prompt for and input employee name
              System.out.println( "Please enter employee name: " );
              String nameOfEmployee = input.next(); // read user input
              // prompt for and input hours worked
              System.out.println( "Enter hours worked: ");
{color:#ff0000}              if( input.nextDouble( <= 0 ) ) // compare input for positive numbers
                  System.out.println( "Only positive numbers are allowed. " +
                          "Please enter a correct number." ); // alert user positive numbers needed
              numberHours = input.nextDouble(); // prompt for hours
              else{
              // prompt for and input hourly pay amount
              System.out.println( "Enter hourly rate: ");
              if(input.nextDouble( <= 0)) // compare input for positive numbers
                  System.out.println( "Only positive numbers are allowed. " +
                          "Please enter a correct number.") // alert user positive numbers are needed
              payRate = input.nextDouble(); // prompt for rate of pay
              else{
              // call PayScale
              double weeklyPay = thisPay.payScale( payRate, numberHours );
              // call currentPayroll's displayMesage method and
              // pass nameOfEmployee as an argument
              currentPayroll.displayMessage( nameOfEmployee, weeklyPay );
{color}             
              System.out.println( "Would you like to exit this program? " +
                      "Enter Y for yes and N for no." );
              exitPayroll = input.next(); // read user input
           } // end while loop
      System.out.println( "Thank you for using this payroll program." );        
    } // end main
} // end class WeeklyPayrollTest

Answer 1

if( input.nextDouble( )  <= 0) // compare input for positive numbers
                  System.out.println( "Only positive numbers are allowed. " +
                          "Please enter a correct number." ); // alert user positive numbers needed
                  numberHours = input.nextDouble(); // prompt for hours
}This will through away the result. Try this
numberHours = input.nextDouble;
while ( input.nextDouble( )  <= 0) // compare input for positive numbers
                  System.out.println( "Only positive numbers are allowed. " +
                          "Please enter a correct number." ); // alert user positive numbers needed
                  numberHours = input.nextDouble(); // prompt for hours
}