java - 超类对象如何调用子类方法

Question

我从同一个超类扩展了 2 个子类，将创建 3 个对象并将其存储到超类的数组中。我想知道如何通过超类对象调用子类方法，我尝试将数据类型从 Ship 转换为 CruiseShip 或 CargoShip，但它不起作用。如果有人可以提供帮助，我将不胜感激。

这是超类：

public class Ship {
   private String name;
   private String year;

   public Ship() {}
   public Ship(String n,String y) {...}
   public void setName() {...}
   public void setYear() {...}
   public void getName() {...}
   public void getYear() {...}
}

这两个子类基本上是一样的。

public class CruiseShip extends Ship {
   private int passenger;
   public CruiseShip() {}
   public CruiseShip() {...}
   public void setPassenager() {...}
   public int getPassenager() {...}
   public Strting showInfo() {this.getName()...etc}
}

public class CargoShip extends Ship {
   private int capacity;
   public CargoShip() {}
   public CargoShip() {...}
   public void setCapacity() {...}
   public int getCapacity() {...}
   public Strting showInfo() {this.getName()...etc}
}

下面是主要方法：

public class report {
   public static void main(String[] args) {
      Ship[] shipList new Ship[3];
      for (int i=0;i<3;i++) {//using for loop to create 3 objects randomly and pass into array}
      for (int i=0;i<3;i++) {
         if (shipList[i] instanceof CruiseShip) {
            ((CruiseShip)shipList[i]).showInfo();  //This way is not work.
         }
         else {
            ((CargoShip)shipList[i]).showInfo();  //This way is not work.
         }

标签： javainheritance

Answer 1

看看多态性和晚期Bindig。基本上后期绑定表示要执行的适当方法是在运行时根据对象的实际类型确定的。所以

class Ship {
  public String showInfo() {return "I'm a ship";}
}

class CruiseShip extends Ship {
  public String showInfo() {return "I'm a cruiseShip";}
}

class CargoShip extends Ship {
  public String showInfo() {return "I'm a cargoShip";}
}

class Main {
  public static void main(String argv[]) {
     Ship[] ships = new Ship[]{new Ship(), new CargoShip(), new CruiseShip()};
     for (Ship ship: ships) {
        System.out.println(ship.showInfo());
        // I'm a ship
        // I'm a cargoShip
        // I'm a cruiseShip
     }
  }
}