如何在java中保存和打开文件（在cmd中）
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【中文标题】如何在java中保存和打开文件（在cmd中）【英文标题】：How to save & open file in java ( in cmd) 【发布时间】：2015-03-18 16:12:14 【问题描述】：我对编程完全陌生，这是我的第一个项目。到目前为止，我已经创建了 3 个类。我的主类允许用户输入数字（来自 kbentry 类），这些数字将被计算（使用 Calculating 类中的方法）以获得结果。现在我只需要将结果保存到一个目录，然后以后可以打开它。我在cmd中运行它。任何帮助表示赞赏。
//计算类
public class CalculatingRocketFlightProfile //Calculation class
//Declaring variables
public double totalImpulse ;
public double averageImpulse;
public double timeEjectionChargeFires;
public double massEmptyVehicle;
public double engineMass;
public double fuelMass;
//Declaring variables for outputs
public double theAverageMassOfTheVehicle; //declare variables to store results of calculations
public double theVehiclesMaximumVelocity;
//Declaring variables of outputs
public double Gravity = 9.81; //Constant variable (default)
//Constructor
public CalculatingRocketFlightProfile(double totalImpulse, double averageImpulse, double timeEjectionChargeFires, double massEmptyVehicle,
double engineMass, double fuelMass) //Setting the parameters
this.totalImpulse = totalImpulse;
this.averageImpulse = averageImpulse;
this.timeEjectionChargeFires = timeEjectionChargeFires;
this.massEmptyVehicle = massEmptyVehicle;
this.engineMass = engineMass;
this.fuelMass = fuelMass;
//Mutators and Accessors
//Accessors
//Methods for calculations - Calculating outputs, using inputs.
public double theAverageMassOfTheVehicle()
return massEmptyVehicle + ((engineMass + (engineMass - fuelMass) ) / 2 ); //Formula to calculate Average mass
//method
public double theVehiclesMaximumVelocity() //Formula to calculate Maximum velocity
return totalImpulse / theAverageMassOfTheVehicle();
//method
//主类
public class Main //Master class
public static void main( String args[] ) //Standard header for main method
kbentry input = new kbentry(); //Creates object of kbentry class
System.out.print("\nPlease enter a number for Total Impulse: " ); //Print message to enter 1. input
double totalImpulse = input.totalImpulse1(); //Holds the variable entered
System.out.println("You have entered : " + totalImpulse); //Shows the variable entered
System.out.print("\nPlease enter a number for Average mass: " ); //Print message to enter 2. input
double averageImpulse = input.averageImpulse2(); //Holds the variable entered
System.out.println("You have entered : " + averageImpulse); //Shows the variable entered
System.out.print("\nPlease enter a number for Time ejection charge fires: " ); //Print message to enter 3. input
double timeEjectionChargeFires = input.timeEjectionChargeFires3(); //Holds the variable entered
System.out.println("You have entered : " + timeEjectionChargeFires); //Shows the variable entered
System.out.print("\nPlease enter a number for the Mass of the empty vehicle: " ); //Print message to enter 4. input
double massEmptyVehicle = input.massEmptyVehicle4(); //Holds the variable entered
System.out.println("You have entered : " + massEmptyVehicle); //Shows the variable entered
System.out.print("\nPlease enter a number for the Mass of the engine: " ); //Print message to enter 5. input
double engineMass = input.engineMass5(); //Holds the variable entered
System.out.println("You have entered : " + engineMass); //Shows the variable entered
System.out.print("\nPlease enter a number for the Mass of the fuel: " ); //Print message to enter 6. input
double fuelMass = input.fuelMass6(); //Holds the variable entered
System.out.println("You have entered : " + fuelMass); //Shows the variable entered
CalculatingRocketFlightProfile calculations = new CalculatingRocketFlightProfile(totalImpulse,averageImpulse, timeEjectionChargeFires,
massEmptyVehicle, engineMass, fuelMass); //Giving the object parameters required from constructor
//Print out lines showing the result.
System.out.println("\nThe average mass of the vehicle: " +calculations.theAverageMassOfTheVehicle() /1000 + " g" +
"\nThe vehicles maximum velocity: " + calculations.theVehiclesMaximumVelocity() * 1000 + " m/s");
//This is what I want to be saved and opened later.
//kb 入口类（所有输入的方法相同，例如averageImpulse2、timeEjectionChargeFires3....等）
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
public class kbentry //Class name
double totalImpulse1() //Method for 1. input
BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); //Creates BufferedReader object for System.in
//Total Impulse entry
String strTotalImpulse = null; // These must be initialised
double intTotalImpulse = 0; //Setting it double
try
strTotalImpulse = in.readLine(); //Reads string value from the keyboard
catch (IOException ioe) // ignore exception
try
intTotalImpulse = Double.parseDouble(strTotalImpulse); // convert it to double
catch (NumberFormatException nfe)
System.out.println("Error! Please enter a number!" + nfe.toString()); //Error message if its not a double
System.out.print("\nPlease enter a number for Total Impulse: "); //again ask for input again
return totalImpulse1(); //Returns value, so it can be re-entered
return intTotalImpulse; //return value
【问题讨论】：
【参考方案1】：我自己在制作类似程序时遇到了这个问题。您将要使用 FileWriter，类似于下面的代码，我不知道您想要这个，但这里是如何将文件写入（和创建）到（现有）目录：
final File file = new File("C:\\path\\to\\dir");
file.createNewFile();
FileWriter fileOut = new FileWriter(file.getAbsoluteFile(), true);
fileOut.write("Here is where you write to the file";
/*you can write to the file again with out erasing the contents by
* using the .append() method*/
fileOut.close();
另外，您是在使用 eclipse，还是在 cmd 中进行编码。如果是这样，你应该得到日食。您还需要在 main 中导入 File (java.io) 和 FileWriter 类。
你应该把它放在这段代码的 sn-p 下：
//Print out lines showing the result.
System.out.println("\nThe average mass of the vehicle: " +calculations.theAverageMassOfTheVehicle() /1000 + " g" +
"\nThe vehicles maximum velocity: " + calculations.theVehiclesMaximumVelocity() * 1000 + " m/s");
//This is what I want to be saved and opened later.
像这样：
//Print out lines showing the result.
System.out.println("\nThe average mass of the vehicle: " +calculations.theAverageMassOfTheVehicle() /1000 + " g" +
"\nThe vehicles maximum velocity: " + calculations.theVehiclesMaximumVelocity() * 1000 + " m/s");
String theAverageMass = "The average mass of the vehicle: " +calculations.theAverageMassOfTheVehicle() /1000 + " g";
String theMaxVelocity = "\nThe vehicles maximum velocity: " + calculations.theVehiclesMaximumVelocity() * 1000 + " m/s"
//This is what I want to be saved and opened later.
final File file = new File("C:\\path\\to\\dir\\yourSaveFile.txt");
file.createNewFile();
FileWriter fileOut = new FileWriter(file.getAbsoluteFile(), true);
fileOut.write(theAverageMass+theMaxVelocity);
/*you can write to the file again with out erasing the contents by
* using the .append() method*/
fileOut.close();
你的主类应该是（带有适当的导入）：
public class Main //Master class
public static void main( String args[] ) //Standard header for main method
kbentry input = new kbentry(); //Creates object of kbentry class
System.out.print("\nPlease enter a number for Total Impulse: " ); //Print message to enter 1. input
double totalImpulse = input.totalImpulse1(); //Holds the variable entered
System.out.println("You have entered : " + totalImpulse); //Shows the variable entered
System.out.print("\nPlease enter a number for Average mass: " ); //Print message to enter 2. input
double averageImpulse = input.averageImpulse2(); //Holds the variable entered
System.out.println("You have entered : " + averageImpulse); //Shows the variable entered
System.out.print("\nPlease enter a number for Time ejection charge fires: " ); //Print message to enter 3. input
double timeEjectionChargeFires = input.timeEjectionChargeFires3(); //Holds the variable entered
System.out.println("You have entered : " + timeEjectionChargeFires); //Shows the variable entered
System.out.print("\nPlease enter a number for the Mass of the empty vehicle: " ); //Print message to enter 4. input
double massEmptyVehicle = input.massEmptyVehicle4(); //Holds the variable entered
System.out.println("You have entered : " + massEmptyVehicle); //Shows the variable entered
System.out.print("\nPlease enter a number for the Mass of the engine: " ); //Print message to enter 5. input
double engineMass = input.engineMass5(); //Holds the variable entered
System.out.println("You have entered : " + engineMass); //Shows the variable entered
System.out.print("\nPlease enter a number for the Mass of the fuel: " ); //Print message to enter 6. input
double fuelMass = input.fuelMass6(); //Holds the variable entered
System.out.println("You have entered : " + fuelMass); //Shows the variable entered
CalculatingRocketFlightProfile calculations = new CalculatingRocketFlightProfile(totalImpulse,averageImpulse, timeEjectionChargeFires,
massEmptyVehicle, engineMass, fuelMass); //Giving the object parameters required from constructor
//Print out lines showing the result.
System.out.println("\nThe average mass of the vehicle: " +calculations.theAverageMassOfTheVehicle() /1000 + " g" +
"\nThe vehicles maximum velocity: " + calculations.theVehiclesMaximumVelocity() * 1000 + " m/s");
String theAverageMass = "The average mass of the vehicle: " +calculations.theAverageMassOfTheVehicle() /1000 + " g";
String theMaxVelocity = "\nThe vehicles maximum velocity: " + calculations.theVehiclesMaximumVelocity() * 1000 + " m/s";
//This is what I want to be saved and opened later.
final File file = new File("C:\\path\\to\\dir\\yourSaveFile.txt");
file.createNewFile();
FileWriter fileOut = new FileWriter(file.getAbsoluteFile(), true);
fileOut.write(theAverageMass+theMaxVelocity);
/*you can write to the file again with out erasing the contents by
* using the .append() method*/
fileOut.close();
【讨论】：
我正在使用 Notepad++ 编写代码，并在 CMD 中编译它。感谢您的代码，我会试一试并让您知道。我是在我的主要课程中使用它还是在单独的课程中使用它？ 我不太清楚如何处理这段代码，你能告诉我应该在哪里包含它吗？ 当然！请给我一点时间来弄清楚。我还没有完全阅读你的代码。 对不起，我的答案还没写完，我先走了，我会在一个小时左右发布。 我是否在 main 中或之外包含 final Final final = new File (etc...) 行？以上是关于如何在java中保存和打开文件（在cmd中）的主要内容，如果未能解决你的问题，请参考以下文章