Java科学符号e和e +？

Question

I'm reading the Oracle's java tutorial. In the Enum Types section, the sample code given has both e and e+ notation for floating point numbers. I'm wondering if there is any difference between e and e+. If there is no, why would they write in such way? Please refer to line 2 to 9. Thanks!

Enum Types

public enum Planet {
        MERCURY (3.303e+23, 2.4397e6),
        VENUS   (4.869e+24, 6.0518e6),
        EARTH   (5.976e+24, 6.37814e6),
        MARS    (6.421e+23, 3.3972e6),
        JUPITER (1.9e+27,   7.1492e7),
        SATURN  (5.688e+26, 6.0268e7),
        URANUS  (8.686e+25, 2.5559e7),
        NEPTUNE (1.024e+26, 2.4746e7);

        private final double mass;   // in kilograms
        private final double radius; // in meters
        Planet(double mass, double radius) {
            this.mass = mass;
            this.radius = radius;
        }
        private double mass() { return mass; }
        private double radius() { return radius; }

        // universal gravitational constant  (m3 kg-1 s-2)
        public static final double G = 6.67300E-11;

        double surfaceGravity() {
            return G * mass / (radius * radius);
        }
        double surfaceWeight(double otherMass) {
            return otherMass * surfaceGravity();
        }
        public static void main(String[] args) {
            if (args.length != 1) {
                System.err.println("Usage: java Planet <earth_weight>");
                System.exit(-1);
            }
            double earthWeight = Double.parseDouble(args[0]);
            double mass = earthWeight/EARTH.surfaceGravity();
            for (Planet p : Planet.values())
               System.out.printf("Your weight on %s is %f%n",
                                 p, p.surfaceWeight(mass));
        }
    }

Answer 1

没有区别， +是可选的符号值，如果未指定符号，则为默认值，因此e23或e+23都对应于10^23 。