如何处理nullpointer异常？

Question

我的java类中有以下代码。

/*
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 * and open the template in the editor.
 */
package webservice;

import java.util.Iterator;
import java.util.List;


public class Webservice {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        ArrayOfString aar = new ArrayOfString();
        aar.getString().add("1025976002");
        aar.getString().add("1026020904");
        aar.getString().add("1026020704");
        aar.getString().add("1026026201");
        aar.getString().add("1026036901");
        aar.getString().add("");
        ArrayOfStatusContainer status = getStatusList(aar);
        List<StatusContainer> li =  status.getStatusContainer(); 
       Iterator litr=li.listIterator();    
      // System.out.println("Elements in forward directiton");   
       while(litr.hasNext()){  
           StatusContainer test = (StatusContainer)litr.next();
          System.out.println(test.getStatus());       
       } 

    }

    private static ArrayOfStatusContainer getStatusList(webservice.ArrayOfString keys) {
        webservice.AdStatusWS service = new webservice.AdStatusWS();
        webservice.AdStatusWSSoap port = service.getAdStatusWSSoap();
        return port.getStatusList(keys);

    }
}

当我输入空字符串或输入重复的字符串值时，我得到一个nullpointer异常。我已经尝试了一段时间，但到目前为止我找不到任何解决方案。我附上了下面例外的屏幕截图。堆栈跟踪如下：

Sent
Booked
Multiple Errors
Exception in thread "main" java.lang.NullPointerException
In QC
Need correction client
    at webservice.Webservice.main(Webservice.java:34)
Java Result: 1
BUILD SUCCESSFUL (total time: 1 second)

Answer 1

控制台说在第34行抛出了nullpointer异常，这可能意味着测试变量为null并且你试图首先访问对象的属性null validate null。

 while(litr.hasNext()){  
       StatusContainer test = (StatusContainer)litr.next();
      if(test != null)
          System.out.println(test.getStatus());       
  } 

Answer 2

确保在从对象访问属性之前始终添加空检查。