Question

为什么我打电话给System.out.println(classroom.toStringLong())时我得到：教室：一个空的大型演讲厅，空为零？

正确的输出应该是：教室：一个大型的演讲厅，门外面是人行道

public class Main {
    public static void main(String[] args) {
        Space classroom = new Space();
         classroom.setName("classroom");
         classroom.setDescription("a large lecture hall");
         Space sidewalk = new Space();
         sidewalk.setName("sidewalk");
         sidewalk.setDescription("a plain concrete sidewalk with weeds growing through the cracks");
         Portal door = new Portal();
         door.setName("door");
         door.setDirection("outside");
         door.setDestination(sidewalk);
         classroom.setPortal(door);
         System.out.println(classroom.toStringLong());
    }
}

public class Space {
  private String _name;
  private String _description;
  private Portal _portal;

  public static void main(String[] args) {
    // TODO Auto-generated method stub

  }
  public String getName() {
    return _name;
  }

  public void setName(String _name){
    this._name=_name;
  }
  public String getDescription() {
    return _description;
  }

  public void setDescription(String _description){
    this._description=_description;
  }
  public Portal getPortal() {
    return _portal;
  }

  public void setPortal(Portal _portal){
    this._portal=_portal;
  }
  public String toString(){
    return _name;
  }
  public String toStringLong(){
    if (_portal!= null){
      Portal p= new Portal();
      p.toStringLong();
      String Longcombined=_name + ": " + _description+" with a "+p.toStringLong();
      return Longcombined;
    }
    else{
      String Long=_name + ": " + _description;
      return Long;
    }
  }
}

public class Portal {
  private String _name;
  private String _direction;
  private Space _destination;

  public String getName() {
    return _name;
  }

  public void setName(String _name){
    this._name=_name;
  }
  public String getDirection(){
    return _direction;
  }
  public void setDirection(String _direction){
    this._direction=_direction;
  }
  public Space getDestination(){
    return _destination;
  }
  public void setDestination(Space _destination){
    this._destination=_destination;
  }
  public String toString(){
    String combined=_name+ " that goes "+_direction;
    return combined;
  }
  public String toStringLong(){
    Space space=new Space();
    String combined=toString() + " to " + space.getDescription() ;
    return combined;
  }

}

Answer 1

您正在创建一个新的空间对象并打印其描述为null 将toStringLong（）方法重写为

In class Space

public String toStringLong(){
if (_portal!= null)
{
// comment this Portal p= new Portal();
_portal.toStringLong();
String Longcombined=_name + ": " + _description+" with a "+_portal.toStringLong();
return Longcombined;
}
else
{
String Long=_name + ": " + _description;
return Long;
}
}


Class Portal ->

public String toStringLong()
{
String combined=toString() + " to " + _destination.getDescription() ;
return combined;
}

希望这能解决您的问题。

Answer 2

运行此代码＆＃34;空格=新空格（）;＆＃34;在toStringLogn（）方法内部，创建了新的空间对象，并且还使用其默认值初始化了此对象的所有即时变量。 String的默认值是＆＃34; null＆＃34;。这就是使用此对象时获得null值的原因。

最好按照以下方式重新定义toStringLong（），

String combined = toString（）+＆＃34;到＆＃34; + _destination.getDescription（）;
返回合并;

为什么我得到一个空？

2 个答案: