A little help please..It does only loop on the first conversion which is in "miles".

package If_then_Else; import javax.swing.*; public class If_then_Else { static final double km_per_miles = 1.6093; static final double meter_per_miles = 1.6093; static final double feet_per_miles = 5279.85565107; static final double inches_per_miles = 63358.26781284; static final double cm_per_miles = 160930.0002446136; static final double miles_per_km = 0.6213882; static final double meter_per_km = 1000; static final double feet_per_km = 3280.8399; static final double inches_per_km = 39370.07; static final double miles_per_meter = 621.3882; static final double km_per_meter = 1000; static final double feet_per_meter = 3.280839; static final double inches_per_meter = 39.3700788; static final double cm_per_meter = 100; static final double miles_per_feet = 0.0001893991176; static final double km_per_feet = 0.0003048; static final double meter_per_feet = 0.3048; static final double inches_per_feet = 12; static final double cm_per_feet = 30.48; static final double miles_per_inches = 0.000015783254; static final double km_per_inches = 0.000025349; static final double meter_per_inches = 0.02534; static final double feet_per_inches = 0.08333; static final double cm_per_inches = 2.51; static final double miles_per_cm = 0.000006218797; static final double km_per_cm = 0.000004; static final double meter_per_cm = 0.004; static final double feet_per_cm = 0.032808386877; static final double inches_per_cm = 0.3937008; public static void main(String[] args) { String opt = JOptionPane.showInputDialog(null, "1. Miles\n2. Kilometers\n3. Meters\n4. Feet\n5. Inches\n6. Centimters\n\nDesired Choice:"); double cm; while (opt != null) { String milesStr; double km; double meters; double feet; double inches; double miles; milesStr = JOptionPane.showInputDialog(null, "Number of Miles:"); miles = Double.parseDouble(milesStr); km = miles * km_per_miles; meters = miles * meter_per_miles; feet = miles * feet_per_miles; inches = miles * inches_per_miles; cm = miles * cm_per_miles; JOptionPane.showMessageDialog(null,km + " miles\n" + meters + " miles\n" + feet + " miles\n" + inches + " miles\n" + cm + " miles"); String kmStr; kmStr = JOptionPane.showInputDialog(null, "Number of Kilometers:"); km = Double.parseDouble(kmStr); miles = km * miles_per_km; meters = km * meter_per_km; feet = km * feet_per_km; inches = km * inches_per_km; JOptionPane.showMessageDialog(null,miles + " km\n" + meters + " km\n" + feet + " km\n" + inches + " km"); String metersStr; metersStr = JOptionPane.showInputDialog(null, "Number of Meters:"); meters = Double.parseDouble(metersStr); miles = meters * miles_per_meter; km = meters * km_per_meter; feet = meters * feet_per_meter; inches = meters * inches_per_meter; cm = meters * cm_per_meter; JOptionPane.showMessageDialog(null,miles + " meters\n" + km + " meters\n" + feet + " meters\n" + inches + " meters\n" + cm + " meters"); String feetStr; feetStr = JOptionPane.showInputDialog(null, "Number of Feet:"); feet = Double.parseDouble(feetStr); miles = feet * miles_per_feet; km = feet * km_per_feet; meters = feet * meter_per_feet; inches = feet * inches_per_feet; cm = feet * cm_per_feet; JOptionPane.showMessageDialog(null,miles + " feet\n" + km + " feet\n" + meters + " feet\n" + inches + " feet\n" + cm + " feet"); String inchesStr; inchesStr = JOptionPane.showInputDialog(null, "Number of Inches:"); inches = Double.parseDouble(inchesStr); miles = inches * miles_per_inches; km = inches * km_per_inches; feet = inches * feet_per_inches; meters = inches * meter_per_inches; cm = inches * cm_per_inches; JOptionPane.showMessageDialog(null,miles + " inches\n" + meters + " inches\n" + feet + " inches\n" + km + " inches\n" + cm + " inches"); String cmStr; cmStr = JOptionPane.showInputDialog(null, "Number of Centimeters:"); cm = Double.parseDouble(cmStr); miles = cm * miles_per_cm; km = cm * km_per_cm; feet = cm * feet_per_cm; inches = cm * inches_per_cm; meters = cm * meter_per_cm; JOptionPane.showMessageDialog(null,km + " cm\n" + feet + " cm\n" + feet + " cm\n" + inches + " cm\n"); } } }