Strange Output in Java

Question

I am in AP Computer Science, and we just learnt how to use our own static methods. This is my second program using them, but this time arrays are involved, and I am getting really weird output. I was hoping that someone could help me figure out why, I assume that I am not properly returning the result array.

The purpose of the program is to calculate the surface gravity of all of the planets in the solar system. The 2 things that I need help with are:

I do not know how to format scientific notation using printf() so that is really messed up.
My gravity array contains [D@7248989f for every number and I can't figure out why.

public static double[] surfaceGravity (double[] r,double[] m) {

    double[] g = new double[r.length];

    for (int count = 0; count < r.length; count++) { 
        g[count] = (6.67 * m[count]) / (r[count] * r[count]);
    }
    return g;
}

public static void printIntro() {
    System.out.printf("%8s%17s%12s%12s%n","Planet","Diameter (km)","Mass (kg)","g (m/s^2)");
    System.out.println("-------------------------------------------------------------------");
}

public static void printData(String[] planet, double[] r, double[] m, double[] g) {
    for (int count = 0; count < r.length; count++) {
        System.out.printf("%9s%9.0f%17.6f%12.2f%n",planet[count],(r[count] * 2),m[count],g[count]);
    }
}

public static void main (String[] args) {
    //initialize arrays
    String[] planetNames = {"Mercury","Venus","Earth","Mars","Jupiter","Saturn","Uranus","Neptune"};
    //double[] mass = {1.0,2.0,3.0,4.0,5.0,6.0,7.0,8.0};
    double[] mass = {3.3E+23,4.87E+24,5.97E+24,6.42E+23,1.9E+27,5.69E+26,8.66E+25,1.03E+26};
    double[] radius = {2440000,6051000,6378000,3397000,71492000,60268000,25559000,24754000};
    double[] gravity = surfaceGravity(radius,mass);

    printIntro();
    printData(planetNames, radius, mass, gravity);
    //I added the line below to test the contest of my gravity array
    for (double grav: gravity) {
        System.out.println(gravity);
    }
}

Because I can't post images, I am not sure how to get the output on here to appear as it does on my computer. This is my full code, so that only thing that you have to do to see my output is to stick this all into a class and run it.

In closing: Yes I am a noob, but I hope that you guys can help me.

That's the result of `Object#toString()`. Look it up for array types. — Sotirios Delimanolis, Jan 04 '14 at 04:14
You're printing the array (`gravity`) in the for loop instead of the `double` (`grav`), which gives you the default `Object.toString()` since the array class doesn't override it. — Brian Roach, Jan 04 '14 at 04:16

score 6 · Answer 1 · answered Jan 04 '14 at 04:14

6

I think you must change this:

for (double grav: gravity) {
    System.out.println(gravity);
}

to:

for (double grav: gravity) {
    System.out.println(grav);
}

because you want to print the elements, not the array.

answered Jan 04 '14 at 04:14

Christian Tapia

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score 0 · Answer 2 · answered Jan 04 '14 at 05:10

You're printing the Array reference, instead of the Array values - You could modify your for loop,

for (double grav : gravity) {
  System.out.println(grav);
}

or you could eliminate that loop by using Arrays.toString(double[]) like so -

System.out.println(java.util.Arrays.toString(gravity));

Strange Output in Java

2 Answers2