Question

我不确定为什么我要为String数组获取java.lang.NullPointerException？我找了好几个小时但找不到任何问题。请帮忙

private String[] stringList;
int j = 0;
StringClass stringRef = new StringClass();

while (//As long as there is string available from what I am reading in)
{
        str = //String read in;
        stringRef.setString(str);
        stringList[j] = stringRef.returnString(); //Shows that this line is the error
        j++;
}

这是班级：

public class StringClass {

   private String stringNew;

   public void setString(String newStr){
      stringNew = newStr;
   }

   public String returnString(){
      return stringNew;
  }
}

Answer 1

即使它位于变量List的名称中，您也没有使用stringList。列表将动态调整大小，因此您不必在编译时声明初始大小。

以下是我建议更改的代码：

import java.util.ArrayList;
import java.util.List;

...

private List<String> stringList = new ArrayList<String>();
int j = 0;
StringClass stringRef = new StringClass();

while (//As long as there is string available from what I am reading in)
{
        str = //String read in;
        stringRef.setString(str);
        stringList.add(stringRef.returnString()); //Shows that this line is the error
        j++;
}

为什么我得到一个String数组的java.lang.NullPointerException？

1 个答案: