Java - 通过 toString() 方法以特定格式打印 ArrayList 对象

Question

我正在制作一个太阳系模型，该模型通过使用类来使用不同的太阳系和行星组。我选择使用数组列表来存储太阳系内行星的每个物体，尽管现在我正在努力以合适的格式输出数据。

我在 toString() 方法中寻找的格式是“行星 X 的质量为 A 个地球，距其恒星的 BAU 为 C 年，轨道为 C 年:可能适合居住吗？” D'

我尝试使用 for 循环来打印每个行星，但不相信这是正确的方法，因为返回会导致循环停止。非常感谢

SolarSystem.java

import java.util.ArrayList;
public class SolarSystem {

    private String systemName;
    private double systemLuminosity;


    public SolarSystem(String name, double luminosity) {
        this.systemName = name;
        this.systemLuminosity = luminosity;
    }

    ArrayList<Planet> list = new ArrayList<>();

    public void addPlanet(String name, double mass, double distance) {

        list.add(new Planet(name, mass, distance, systemLuminosity));

    }

    public void planetProperties() {

    }

    public String toString() {
        System.out.println(list.size());
        String results = "+";
        for (Planet planet : list) {
            results += planet.getName(); //if you implement toString() for Dog then it will be added here
        }
        return results;
    }
}

Planet.java

    public class Planet {

        private String planetName;
        private double planetMass;
        private double distanceFromStar;
        private double orbitalPeriod;
        private String isHabitable;

        public Planet(String name, double mass, double distance, double systemLuminosity) {

            setName(name);
            setMass(mass);
            setDistanceFromSun(distance);
            setOrbitalPeriod(distance);
            setIsHabitable(mass, distance, systemLuminosity);


        }

        public void setName(String name) {
            planetName = name;
        }

        public  String getName() {
            return planetName;
        }

        public  void setMass(double mass) {
            planetMass = mass;
        }

        public double getMass() {
            return planetMass;
        }

        public void setDistanceFromSun(double distance) {
            distanceFromStar = distance;
        }

        public double getDistanceFromStar() {
            return distanceFromStar;
        }

        public void setOrbitalPeriod(double distance) {
            orbitalPeriod = Math.sqrt(distance*distance*distance);
        }

        public double getOrbitalPeriod() {
            return orbitalPeriod;
        }

        public void setIsHabitable(double mass, double distance, double luminosity) {
            if (mass >= 0.6 && mass <= 7.0) {
                if ((distance >= 0.75 * Math.sqrt(luminosity)) && (distance <= 2.0 * Math.sqrt(luminosity))) {
                    isHabitable = "yes";
                } else {
                    isHabitable = "no";
                }
            } else {
                isHabitable = "no";
            }

        }

        public String getIsHabitable() {
            return isHabitable;
        }
    }

Main.java

public class Main {

    public static void main(String[] args) {

        //Create our solar system
        SolarSystem ourSystem = new SolarSystem("Our System",1.0);

        //Add planets in our solar system
        ourSystem.addPlanet("Mercury", 0.055, 0.387);
        ourSystem.addPlanet("Venus", 0.815, 0.723);
        ourSystem.addPlanet("Earth", 1.0, 1.0);
        ourSystem.addPlanet("Mars", 0.107, 1.52);
        ourSystem.addPlanet("Jupiter", 317.8, 5.20);
        ourSystem.addPlanet("Saturn", 95.2, 9.58);
        ourSystem.addPlanet("Uranus", 14.5, 19.20);
        ourSystem.addPlanet("Neptune", 17.1, 30.05);

        System.out.println(ourSystem.toString());



    }
}

Answer 1

您需要在 Planet 类中实现 toString() 方法，例如:

class Planet {
    private String planetName;
    private double planetMass;
    private double distanceFromStar;
    private double orbitalPeriod;
    private String isHabitable;

    @Override
    public String toString() {
        return String.format(
                "Planet %s has a mass of %f Earths, is %f from its star, and orbits in %f years: could be habitable? %s%n",
                this.planetName, this.planetMass, this.distanceFromStar, this.orbitalPeriod, this.isHabitable);
    }

}

然后在您的 SolarSystem 类中，您可以创建一个包含类似内容的列表，您已经拥有该部分几乎正确的部分，但我已将 getName 更改为 toString :

@Override
public String toString() {
    StringBuilder buf = new StringBuilder();

    for (Planet planet : list) {
        buf.append(planet);
    }

    return buf.toString();
}