PrintWriter将文本添加到文件 [英] PrintWriter add text to file

问题描述

在我的在线计算机科学课上，我必须编写一个程序来确定太阳系中每个星球上的表面引力。我已经几乎得到了它的每一个方面的工作，保存一个。我需要使用单独的方法将表面引力写入文件。这是我现在的方法：

pre $ public $ {

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

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





$ b我的问题是，当我把它写入一个文件时，它会覆盖以前的值。我如何得到它包括所有的值。这是我的代码的全部，如果有帮助：

  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，行星名，直径Km，质量Kg，g）; 
 
 
 $ b public static void writeResultsToFile（double g）throws IOException {
 
 PrintWriter outFile = new PrintWriter（new File（planetaryData.txt ））; 
 
 outFile.printf（％。2f％n，g）; 
 outFile.close（）; 
 
 $ b $ public static void main（String [] args）throws IOException {
 //变量
 String [] planetName = new String [8]; 
 planetName [0] =水星; 
 planetName [1] =Venus; 
 planetName [2] =地球; 
 planetName [3] =火星; 
 planetName [4] =木星; 
 planetName [5] =土星; 
 planetName [6] =天王星; 
 planetName [7] =海王星; 
 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数组= 0; 
 $ b $ // code 
 
 System.out.printf（％s％20s％15s％15s％n，Planet，Diameter（km），质量（kg），g（m / s ^ 2））; 
 
（double d：diameterKm）{
 g [array] = calculateSurfaceGravity（d，massKg [array]）; 
 printResultsToScreen（planetName [array]，d，massKg [array]，g [array]）; 
 writeResultsToFile（g [array]）; 
 array ++; 
 
 
 
 
 $ b $ div class =h2_lin>解决方法

这样做是为了在追加模式下创建 PrinterWriter 使用 FileWriter



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




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++;
    }
}

}

解决方案

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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