spenserpro spenserpro - 4 months ago 26
Java Question

PrintWriter add text to file

In my online computer science class I have to write a program to determine the surface gravity on each planet in the solar system. I have gotten almost every aspect of it to work save one. I need to write the surface gravity to a file using a separate method. This is my current method:

public static void writeResultsToFile(double g) throws IOException{

PrintWriter outFile = new PrintWriter(new File("planetaryData.txt"));

outFile.printf("%.2f%n", g);
outFile.close();
}


My problem is that when I write it to a file it will overwrite the previous value. How do I get it include all of the values. Here is the entirety of my code if that helps:

import java.util.Scanner;
import java.io.PrintWriter;
import java.io.IOException;
import java.io.File;


public class gravityV1 {

/**
* @param args
*/

public static double calculateSurfaceGravity(double d, double M){
double G = 6.67 * Math.pow(10, -11);
double r = d;
double g;

g = G * M/Math.pow(r/2*1000, 2);

return g;
}

public static void printResultsToScreen(String planetName, double diameterKm, double massKg, double g){

System.out.printf("%-15s%-17.0f%-17.2e%.2f%n", planetName, diameterKm, massKg, g);

}

public static void writeResultsToFile(double g) throws IOException{

PrintWriter outFile = new PrintWriter(new File("planetaryData.txt"));

outFile.printf("%.2f%n", g);
outFile.close();
}

public static void main(String[] args) throws IOException {
// Variables
String [] planetName = new String[8];
planetName[0] = "Mercury";
planetName[1] = "Venus ";
planetName[2] = "Earth ";
planetName[3] = "Mars ";
planetName[4] = "Jupiter";
planetName[5] = "Saturn ";
planetName[6] = "Uranus ";
planetName[7] = "Neptune";
double [] diameterKm = new double[8];
diameterKm[0] = 4880;
diameterKm[1] = 12103.6;
diameterKm[2] = 12756;
diameterKm[3] = 6794;
diameterKm[4] = 142984;
diameterKm[5] = 120536;
diameterKm[6] = 51118;
diameterKm[7] = 49532;
double [] massKg = new double[8];
massKg[0] = 3.30 * Math.pow(10, 23);
massKg[1] = 4.869 * Math.pow(10, 24);
massKg[2] = 5.97 * Math.pow(10, 24);
massKg[3] = 6.4219 * Math.pow(10, 23);
massKg[4] = 1.900 * Math.pow(10, 27);
massKg[5] = 5.68 * Math.pow(10, 26);
massKg[6] = 8.683 * Math.pow(10, 25);
massKg[7] = 1.0247 * Math.pow(10, 26);
double [] g = new double[8];
int array = 0;

//code

System.out.printf("%s%20s%15s%15s%n", "Planet", "Diameter (km)", "Mass (kg)", "g (m/s^2)");

for(double d : diameterKm){
g[array] = calculateSurfaceGravity(d, massKg[array]);
printResultsToScreen(planetName[array], d, massKg[array], g[array]);
writeResultsToFile(g[array]);
array++;
}
}

}

Answer

Do this in order to create a PrinterWriter working with a FileWriter in append mode:

PrintWriter outFile = new PrintWriter(new FileWriter("planetaryData.txt", true)); 
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