Question

假设我有一个Warehouse类。该仓库有一个TradeDesk。 TradeDesk根据Warehouse中设置的实例变量计算要销售的可用项目。 Warehouse的构造函数实例化TradeDesk，但由于TradeDesk需要来自未完全初始化的Warehouse的实例变量，因此我们遇到了问题。没有通过多个构造函数传递实例值（我宁愿避免;注意下面的示例显着简化），我该如何解决？谢谢！

public class Warehouse {
    TradingDesk td;
    public int val;

    public Warehouse() {
        val = 3;
        td = new TradingDesk(this);
    }
// New class
public class TradingDesk {
    Warehouse associatedWh;
    int val;
    public TradingDesk(Warehouse wh) {
        associatedWh = wh;
        val = associatedWh.val;
    }
}

}

Answer 1

关于您的内部类代码，您尝试使用外部类的实例初始化Warehouse字段。所以代码变成了：

public class Warehouse {
    private TradingDesk td = new TradingDesk();
    private int val = 3;

    class TradingDesk {
         // you have already access to the outer Warehouse class including its fields
    }
}

实际上，内部类可以访问外部类的所有属性。所以你的问题就消失了。

修改------------------

这里是我处理循环依赖的解决方案：

public class Warehouse { private TradingDesk td = new TradingDesk(); private int val = 3; public int getVal(){ //so accessible through TradingDesk object return val; } public void associateWhToTd(){ td.setAssociatedWh(this); // no issue here since "this" is fully already created } public static void main(String[]args){ // example of usage Warehouse wh = new Warehouse(); wh.associateWhToTd(); } } public class TradingDesk { Warehouse associatedWh; public void setAssociatedWh(Warehouse wh){ this.associatedWh = wh; } }

Answer 2

好吧，你可以使TradingDesk成为WareHouse的内部类。通过这种方式，它可以直接访问其封闭的WareHouse实例变量，而无需传递任何参数，并且只能在WareHouse实例的上下文中创建它的实例。

public class Warehouse {

    private int val;
    private TradingDesk td;

    public Warehouse() {
        this.val = 3;
        this.td = new TradingDesk();
    }

    public class TradingDesk {

        public TradingDesk() {
            //this is the right way to access the enclosing instance
           if(WareHouse.this.val==3){
               //do something
           }
        }

        public WareHouse getAssociatedWareHouse(){
           return WareHouse.this;
        }
    }
}

Answer 3

您可以使用延迟实例化的子对象：

class Warehouse {
  private TradingDesk td;
  ...

  public Warehouse() {
    ...
  }

  public TradingDesk getTradingDesk() {
    if (td == null) td = new TradingDesk(this);
    return td;
  }
}

请注意，上面的getter不是线程安全的。

Don't escape this during construction

使用未完全初始化的'this'作为参数实例化对象

3 个答案: