java - 将数据从主方法导入到另一个方法中，然后在再次运行程序之前存储该值

Question

我有两个类，一个只有一个 main(String args[]) 方法，另一个则包含所有其余方法。我试图将主方法中的数据获取到第二个类中来运行它，然后将信息返回给主方法。我的程序正在编译，但每次我输入新数字时数字应该会下降，但事实并非如此。任何帮助表示赞赏!

public class LunarLander
{
  public static void move(double efficiency, double fuelLeft, int maxFuel, int time, double Altitude, double inputFuelRate)
  {
    //formulas to change outputs
    double velocity = time * (efficiency - 1.62); //given formula to caluculate velocity
    double altChng = time * velocity; //creates a variable for atitude chage 

    //exceptions
    if (efficiency > 0 && fuelLeft == 0){ //changes efficiency to 0 when there is no fuel left
      efficiency = 0;
    }
    else{
    }

    //new outputs
    Altitude = Altitude - altChng; //calculates new altitude by subtracting altitude change
    velocity = time * (efficiency - 1.62); //given formula to caluculate velocity
    altChng = time * velocity; //creates a variable for atitude chage 
    double verticalSpeed = velocity; //since the ship would only move and not go back and forth velocity is speed

    efficiency = inputFuelRate / maxFuel; //recalculates efficiency

    double fuelLoss = time * fuelLeft * maxFuel;// new variable to determine how much fuel was burned during time period
    fuelLeft = fuelLeft - fuelLoss; //changes the values for fuel left

  }

  public static boolean crashed(double Altitude, double verticalSpeed)
  {
    if (Altitude == 0 && verticalSpeed <-1){
      return true;
    }
    else{
      return false;
    }
  }

  public String toString(double Altitude, double verticalSpeed, double fuelLeft){
    String output = "";
    output += "Eagle: \n";
    output += "Altitude = " + Altitude + "\n";
    output += "Speed = " + verticalSpeed + "\n";
    output += "Fuel = " + fuelLeft + "\n";

    return output;
  }

}

主要方法:

import java.util.Scanner;

public class Pilot
{

  public static void main(String args[])
  {
    Scanner kb = new Scanner(System.in);

    LunarLander lander = new LunarLander(); // create a LunarLander object 
    double Altitude = 10.0;

    String Name = "Eagle";

    double fuelLeft = 1000.0;

    int shipWeight = 400;

    int maxThrust = 10000;

    int verticalSpeed = 0;

    double efficiency = 0;

    int maxFuel = 400; //max fuel flow

    System.out.println("Initial data: ");
    System.out.println("Altitude = " + Altitude);
    System.out.println("Speed = " + verticalSpeed);
    System.out.println("Fuel = " + fuelLeft);

    while (lander.crashed(Altitude, verticalSpeed) != true && Altitude > 0)
    {

      System.out.println("Please enter a time in seconds: ");
      int time = kb.nextInt();
      System.out.println("Please enter a fuel rate between 0 and 1");
      double inputFuelRate = kb.nextDouble();
      System.out.println("Input time increment: " + time);
      System.out.println("Input fuel rate: " + inputFuelRate);

      lander.move(efficiency, fuelLeft, maxFuel, time, Altitude, inputFuelRate);


      System.out.println(lander.toString(Altitude, verticalSpeed, fuelLeft));
    }

  }
}

Answer 1

您的方法变量 Altitude 是该方法的本地变量。这意味着每次调用该方法时都会重新创建并重新分配值。在java中，方法的所有参数都是按值传递的，这意味着方法内部参数的变化在方法外部是不可见的，基本上它在调用时创建参数的副本。您需要通过在类中而不是在任何方法中定义来使其成为实例变量。对于每次调用该方法时想要更改的其他变量也是如此。

import java.util.Scanner;

public class Pilot
{

  public static void main(String args[])
  {
    Scanner kb = new Scanner(System.in);


    double Altitude = 10.0;

    String Name = "Eagle";

    double fuelLeft = 1000.0;

    int shipWeight = 400;

    int maxThrust = 10000;

    int verticalSpeed = 0;

    double efficiency = 0;

    int maxFuel = 400; //max fuel flow

    LunarLander lander = new LunarLander(Altitude, verticalSpeed, fuelLeft); // create a LunarLander object

    System.out.println("Initial data: ");
    System.out.println("Altitude = " + Altitude);
    System.out.println("Speed = " + verticalSpeed);
    System.out.println("Fuel = " + fuelLeft);

    while (lander.crashed() != true && Altitude > 0)
    {

      System.out.println("Please enter a time in seconds: ");
      int time = kb.nextInt();
      System.out.println("Please enter a fuel rate between 0 and 1");
      double inputFuelRate = kb.nextDouble();
      System.out.println("Input time increment: " + time);
      System.out.println("Input fuel rate: " + inputFuelRate);

      lander.move(efficiency, maxFuel, time, inputFuelRate);


      System.out.println(lander.toString());
    }

  }
}

以及 LunarLander 级

public class LunarLander {

    double Altitude;
    double verticalSpeed;
    double fuelLeft;

    public LunarLander(double Altitude, double verticalSpeed, double fuelLeft){
        this.Altitude = Altitude;
        this.verticalSpeed = verticalSpeed;
        this.fuelLeft = fuelLeft;
    }

    public void move(double efficiency, int maxFuel,
            int time, double inputFuelRate) {
        // formulas to change outputs
        double velocity = time * (efficiency - 1.62); // given formula to
                                                        // caluculate velocity
        double altChng = time * velocity; // creates a variable for atitude
                                            // chage

        // exceptions
        if (efficiency > 0 && fuelLeft == 0) { // changes efficiency to 0 when
                                                // there is no fuel left
            efficiency = 0;
        } else {
        }

        // new outputs
        Altitude = Altitude - altChng; // calculates new altitude by subtracting
                                        // altitude change
        velocity = time * (efficiency - 1.62); // given formula to caluculate
                                                // velocity
        altChng = time * velocity; // creates a variable for atitude chage
        verticalSpeed = velocity; // since the ship would only move and
                                            // not go back and forth velocity is
                                            // speed

        efficiency = inputFuelRate / maxFuel; // recalculates efficiency

        double fuelLoss = time * fuelLeft * maxFuel;// new variable to determine
                                                    // how much fuel was burned
                                                    // during time period
        fuelLeft = fuelLeft - fuelLoss; // changes the values for fuel left

    }

    public boolean crashed() {
        if (Altitude == 0 && verticalSpeed < -1) {
            return true;
        } else {
            return false;
        }
    }

    public String toString() {
        String output = "";
        output += "Eagle: \n";
        output += "Altitude = " + Altitude + "\n";
        output += "Speed = " + verticalSpeed + "\n";
        output += "Fuel = " + fuelLeft + "\n";

        return output;
    }

}