Unix shell脚本可以用来操作数据库吗？(Can Unix shell script be used to manipulate databases?)

 您的方法变量Altitude是方法的本地变量。 这意味着每次调用方法时都会重新创建和重新分配值。 在java中，方法的所有参数都按值传递，这意味着方法内部参数的更改在其外部不可见，基本上它在调用时会创建参数的副本。 您需要通过在类中定义不在任何方法内部来使其成为实例变量。 每次调用方法时，您希望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());
    }

  }
}
 
 还有LunarLander课程 
 
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;
    }

}

Your method variable Altitude is local to the method. This means its recreated and reassigned value every time you call the method. In java all parameters to a method are passed by value, which means the change in the parameter inside the the method is not visible outside it, basically it creates a copy of the parameter when invoked. You need to make it an instance variable by defining in the class not inside any method. same goes for the other variables that you want to be changed every time you call the method.
 
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());
    }

  }
}
 
And the LunarLander class
 
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;
    }

}