创建对象期间发生Java空指针异常

一切似乎都很好，但我无法在另一个类中创建新对象。我只得到了

“java.lang.Null.Pointer.Exception”

实际上，我有一个F16类，用于创建F16飞机。现在，当我尝试在MainActivity中创建一个新对象来显示飞机时，会显示此错误

main活动类

public class MainActivity extends Activity {    
    LinearLayout Map=null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Map=(LinearLayout)findViewById(R.id.Map);
        try{
        F16 myF16=new F16();        
        myF16.CreateAirCraft(myF16.CoordinateX,myF16.CoordinateY, this, Map);
        }
        catch(Exception ex){
        Log.d("Er", ex.toString());     
        }
    }

public class F16 extends AirCraft {
Context context;
private int Image=context.getResources().getIdentifier("F16" , "drawable", context.getPackageName());
LinearLayout PlaneBody=null;//a container used to hold All information of Aircraft
TextView PlaneName=null;// mentions to AirCraft name
ImageView PlaneImg=null;//mentions to AirCraft Image
public void CreateAirCraft(byte X , byte Y,Context Ctx,LinearLayout Map){
        Name="F-16";    
        PlaneBody=new LinearLayout(Ctx);
        PlaneName=new TextView(Ctx);
        PlaneImg=new ImageView(Ctx);
        PlaneName.setText(Name);
        PlaneImg.setImageResource(Image);
        PlaneBody.addView(PlaneName);
        PlaneBody.addView(PlaneImg);
        Map.addView(PlaneBody);
    }
}

public abstract class AirCraft {
   public String Name="";
   public byte CoordinateX=0;
   public byte CoordinateY=0;
   public byte Weight=0;
}

F16级

public class MainActivity extends Activity {    
    LinearLayout Map=null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Map=(LinearLayout)findViewById(R.id.Map);
        try{
        F16 myF16=new F16();        
        myF16.CreateAirCraft(myF16.CoordinateX,myF16.CoordinateY, this, Map);
        }
        catch(Exception ex){
        Log.d("Er", ex.toString());     
        }
    }

public class F16 extends AirCraft {
Context context;
private int Image=context.getResources().getIdentifier("F16" , "drawable", context.getPackageName());
LinearLayout PlaneBody=null;//a container used to hold All information of Aircraft
TextView PlaneName=null;// mentions to AirCraft name
ImageView PlaneImg=null;//mentions to AirCraft Image
public void CreateAirCraft(byte X , byte Y,Context Ctx,LinearLayout Map){
        Name="F-16";    
        PlaneBody=new LinearLayout(Ctx);
        PlaneName=new TextView(Ctx);
        PlaneImg=new ImageView(Ctx);
        PlaneName.setText(Name);
        PlaneImg.setImageResource(Image);
        PlaneBody.addView(PlaneName);
        PlaneBody.addView(PlaneImg);
        Map.addView(PlaneBody);
    }
}

public abstract class AirCraft {
   public String Name="";
   public byte CoordinateX=0;
   public byte CoordinateY=0;
   public byte Weight=0;
}

飞机等级

public class MainActivity extends Activity {    
    LinearLayout Map=null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Map=(LinearLayout)findViewById(R.id.Map);
        try{
        F16 myF16=new F16();        
        myF16.CreateAirCraft(myF16.CoordinateX,myF16.CoordinateY, this, Map);
        }
        catch(Exception ex){
        Log.d("Er", ex.toString());     
        }
    }

public class F16 extends AirCraft {
Context context;
private int Image=context.getResources().getIdentifier("F16" , "drawable", context.getPackageName());
LinearLayout PlaneBody=null;//a container used to hold All information of Aircraft
TextView PlaneName=null;// mentions to AirCraft name
ImageView PlaneImg=null;//mentions to AirCraft Image
public void CreateAirCraft(byte X , byte Y,Context Ctx,LinearLayout Map){
        Name="F-16";    
        PlaneBody=new LinearLayout(Ctx);
        PlaneName=new TextView(Ctx);
        PlaneImg=new ImageView(Ctx);
        PlaneName.setText(Name);
        PlaneImg.setImageResource(Image);
        PlaneBody.addView(PlaneName);
        PlaneBody.addView(PlaneImg);
        Map.addView(PlaneBody);
    }
}

public abstract class AirCraft {
   public String Name="";
   public byte CoordinateX=0;
   public byte CoordinateY=0;
   public byte Weight=0;
}

---

在F16类中使用上下文作为参数生成构造函数 比如说

public F16(Context context)
{
Image=context.getResources().getIdentifier("F16" , "drawable", context.getPackageName());
}

并从主活动传递上下文

F16 myF16=new F16(this); 

---

NullPointerException

是由

F16

类的第3行引起的

Context context;
private int Image=context.getResources().getIdentifier("F16" , "drawable", context.getPackageName());

字段

context

隐式初始化为

null

。然后初始化

Image

并调用

context.getResources（）

，但由于

context

为空，因此您将获得NPE。

请尝试下面的代码

public class F16 extends AirCraft {

Context context;
private int Image;
LinearLayout PlaneBody=null;//a container used to hold All information of Aircraft
TextView PlaneName=null;// mentions to AirCraft name
ImageView PlaneImg=null;//mentions to AirCraft Image

public F16(Context context)
{
    this.context = context;
    Image=context.getResources().getIdentifier("F16" , "drawable", context.getPackageName());
}

public void CreateAirCraft(byte X , byte Y,Context Ctx,LinearLayout Map){
        Name="F-16";    
        PlaneBody=new LinearLayout(Ctx);
        PlaneName=new TextView(Ctx);
        PlaneImg=new ImageView(Ctx);
        PlaneName.setText(Name);
        PlaneImg.setImageResource(Image);
        PlaneBody.addView(PlaneName);
        PlaneBody.addView(PlaneImg);
        Map.addView(PlaneBody);
    }
}

---

@我只得到了“java.lang.Null.Pointer.Exception”，没有更多！在发布日志之前，使用

Log.d（“Er”，例如toString（），e）启用stacktrace。您怎么可能只得到
java.lang.Null.Pointer.Exception
什么都没有。那是不可能的。你的电话线是什么error@curiousdogPost你这个笨蛋。我认为您的logcat抛出了java.lang.NullPointerExceptionBTW：这就是为什么会出现错误的答案。“Android Weblineindia”已经回答了如何修复它。他在F16 myF16=new F16（）中得到了错误@Andreas@PiyushMittal他是，但是
new F16（）
调用执行字段初始值设定项，并且是初始值设定项导致NPE。它似乎有效，因为它显示飞机的名称，但不显示图像。你认为呢？你缺少了
this.context=context。现在它在构造函数中初始化了，
createAircrafter
方法可能不再需要将
Context
作为参数，当然，除非它可能是不同的上下文。图像存储在哪里？