PrintWriter add text to file
In my online computer science class, I have to write a program to determine the surface gravity on every planet in the solar system. I got almost all aspects of this except one. I need to write 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, when I write it to a file, it overwrites the previous value. How can I get all values. Here is all my code, if it 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++;
}
}
}
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From the Mkyong Tutorials :
FileWriter is a character stream for writing characters to a file. By default, it will replace all existing content with new content, however, when you specified a true (boolean) value as the second argument in the FileWriter constructor, it will preserve the existing content and append the new content to the end of the file.
You can use something like -
PrintWriter outputFile = new PrintWriter(new FileWriter(file, true));
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Two problems:
1) You overwrite the file every time. printResultsToFile
should accept the whole array, not just one datate. Call it from outside the loop.
2) Consider entering floating point numbers as 2.08e24 for brevity.
private void printResultsToFile(double result[]) {
PrintWriter pw = new PrintWriter(new FileWriter("planetaryData.txt"));
for (int i=0; i< result.length; i++) {
pw.printf("%.2f%n", result[i]);
}
pw.close();
}
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