如何访问另一个类中定义的对象？

您需要具有public访问器（获取器），private才能在其他类中访问成员。

如下进行：

import java.util.Scanner;

class Engine {
    String name;
    int year;
    String manufacturer;

    public Engine() {
    }

    public Engine(String name, int year, String manufacturer) {
        this.name = name;
        this.year = year;
        this.manufacturer = manufacturer;
    }

    // getters and setters of instance variables

    @Override
    public String toString() {
        return "Engine [name=" + name + ", year=" + year + ", manufacturer=" + manufacturer + "]";
    }
}

class Submarine {
    private String id;
    private Engine engine;

    public Submarine(String id, Engine engine) {
        this.id = id;
        this.engine = engine;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public void setEngine(Engine engine) {
        this.engine = engine;
    }

    public Engine getEngine() {
        return engine;
    }

    @Override
    public String toString() {
        return "Submarine [id=" + id + ", engine=" + engine + "]";
    }
}

class ShipStorage {
    private Submarine submarine;
    private Submarine[] submarines;

    public void setSubmarine(Submarine submarine) {
        this.submarine = submarine;
    }

    public Submarine getSubmarine() {
        return submarine;
    }

    public void setSubmarines(Submarine[] submarines) {
        this.submarines = submarines;
    }

    public Submarine[] getSubmarines() {
        return submarines;
    }
}

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        ShipStorage store = new ShipStorage();

        // Input submarines
        Submarine[] submarines = new Submarine[3];
        String id, name, manufacturer;
        int year;
        for (int i = 0; i < submarines.length; i++) {
            System.out.print("Enter the ID of the sumarine: ");
            id = in.nextLine();
            System.out.print("Enter the name of its engine: ");
            name = in.nextLine();
            System.out.print("Enter the manufacturing year of its engine: ");
            year = Integer.parseInt(in.nextLine());
            System.out.print("Enter the manufacturer's name of its engine: ");
            manufacturer = in.nextLine();

            submarines[i] = new Submarine(id, new Engine(name, year, manufacturer));
        }

        // Store submarines to ShipStorage
        store.setSubmarines(submarines);

        // Display submarines
        System.out.println("Displaying the data: ");
        for (Submarine submarine : store.getSubmarines()) {
            System.out.println(submarine);
        }
    }
}

运行示例：

Enter the ID of the sumarine: 1
Enter the name of its engine: A
Enter the manufacturing year of its engine: 2010
Enter the manufacturer's name of its engine: X
Enter the ID of the sumarine: 2
Enter the name of its engine: B
Enter the manufacturing year of its engine: 2011
Enter the manufacturer's name of its engine: Y
Enter the ID of the sumarine: 3
Enter the name of its engine: C
Enter the manufacturing year of its engine: 2018
Enter the manufacturer's name of its engine: Z
Displaying the data: 
Submarine [id=1, engine=Engine [name=A, year=2010, manufacturer=X]]
Submarine [id=2, engine=Engine [name=B, year=2011, manufacturer=Y]]
Submarine [id=3, engine=Engine [name=C, year=2018, manufacturer=Z]]

回答来源：Stack Overflow