PrintWriter add text to file
Solution 1
Do this in order to create a PrinterWriter
working with a FileWriter
in append mode:
PrintWriter outFile = new PrintWriter(new FileWriter("planetaryData.txt", true));
Solution 2
From Mkyong's tutorials:
FileWriter, a character stream to write characters to file. By default, it will replace all the existing content with new content, however, when you specified a true (boolean) value as the second argument in FileWriter constructor, it will keep the existing content and append the new content in the end of the file.
You can use something like -
PrintWriter outputFile = new PrintWriter(new FileWriter(file, true));
Admin
Updated on July 21, 2022Comments
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Admin almost 2 years
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++; } } }
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Mel Nicholson over 11 yearsThe problem with this approach is that if you run your program 10 times, you get 10 sets of results in the file.
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OneCricketeer over 2 yearsThis removes previous file content