爪哇 - 从超类ArrayList中挑选出的子类 [英] Java - Sorting out subclass from ArrayList of superclass

问题描述

我有一个包含超类的对象和一些子类对象的ArrayList。让我们把他们subclass1和subclass2。

有没有一种方法我可以去ArrayList和辨别哪些对象是父类，subclass1和subclass2。这样我就可以把它们放进ArrayList和ArrayList的。

这是一个过于简化的版本，但它证明什么，我希望做的事。

 公共类食品{
    私人字符串名称;
    公共食品（字符串名称）{
        this.name =名称;
    }
}公共类布丁扩展食品{
    公共布丁（字符串名称）{
        超（名）;
    }
}公共类早餐食品扩展{
    公共早餐（字符串名称）{
        超（名）;
    }
}公共静态无效的主要（字符串ARGS []）{
    ArrayList的＆LT;食品GT;食品=新的ArrayList（）;    foods.add（新的食品（香肠））;
    foods.add（新的食品（培根））;
    foods.add（新布丁（蛋糕））;
    foods.add（新早餐（面包））;
    foods.add（新布丁（海绵））;
    foods.add（新的食品（米））;
    foods.add（新早餐（鸡蛋））;    ArrayList的＆LT;＆布丁GT; PUD的=新的ArrayList（）;
    ArrayList的＆LT;早餐和GT; wakeupjuices =新的ArrayList（）;    对于（食品F：食品）{
        //如果（f是布丁）{puds.add（F）;}
        //否则，如果（f是早餐）{wakeupjuices.add（F）;}
    }}
 

解决方案

您可以检查所需要的类型，如这样，使用的instanceof 关键字：

 的（食品F：食品）
{
    如果（F的instanceof布丁）
        puds.add（F）;
    否则，如果（F的instanceof早餐）
        wakeupjuices.add（F）;
}
 

I have an ArrayList which contains objects of the super class and some subclass objects. Let's call them subclass1 and subclass2.

Is there a way I can go ArrayList and discern which objects are SuperClass, subclass1 and subclass2. So I can put them into ArrayList and ArrayList.

This is an overly simplified version but it demonstrates what I'm hoping to do.

    public class food{
    private String name;
    public food(String name){
        this.name = name;
    }
}   

public class pudding extends food{
    public pudding(String name){
        super(name);
    }
}

public class breakfast extends food{
    public breakfast(String name){
        super(name);
    }
}

public static void main(String args[]){
    ArrayList<food> foods = new ArrayList();

    foods.add(new food("Sausage"));
    foods.add(new food("Bacon"));
    foods.add(new pudding("cake"));
    foods.add(new breakfast("toast"));
    foods.add(new pudding("sponge"));
    foods.add(new food("Rice"));
    foods.add(new breakfast("eggs"));

    ArrayList<pudding> puds = new ArrayList();
    ArrayList<breakfast> wakeupjuices = new ArrayList();

    for(food f : foods){
        //if(f is pudding){puds.add(f);}
        //else if(f is breakfast){wakeupjuices.add(f);}
    }

}

解决方案

You can check for the desired types like this, using the instanceof keyword:

for (food f : foods)
{
    if (f instanceof pudding)
        puds.add(f);
    else if (f instanceof breakfast)
        wakeupjuices.add(f);
}

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