添加到地图时的Java异常

Question

不确定有什么问题......它应该工作还是可能缺少什么？以下是代码:

public class TestOracleMap implements java.io.Serializable{
static TreeMap<String, Integer> map;
static TreeMap<String, Integer> localMap = new TreeMap<String, Integer>();

public static void StoreMapInDB(TreeMap<String, Integer> map) throws
        IOException, FileNotFoundException{
    try {
  PreparedStatement insertMap = null;
  //String insertString = "INSERT INTO TESTMAP(ID, MPFIELD) VALUES (1, ?)";
  Connection con=null;
  con.setAutoCommit(false);
  Class.forName("oracle.jdbc.driver.OracleDriver");
  con=DriverManager.getConnection(
    "jdbc:oracle:thin:@oXXX",
    "XXX",
    "XXX");

  ByteArrayOutputStream bos = new ByteArrayOutputStream() ;
  ObjectOutputStream out = new ObjectOutputStream(bos);
  out = new ObjectOutputStream(bos) ;
  out.writeObject(map);
  out.close();

  byte[] buf = bos.toByteArray();
  PreparedStatement prepareStatement = con.prepareStatement("insert into  

  TESTMAP(ID,MAPFIELD)values(?,?)");
  prepareStatement.setLong(1, 1);
  prepareStatement.setBinaryStream(2, new ByteArrayInputStream(buf), buf.length);



 // insertMap.executeUpdate();
  con.commit();
    } catch(Exception e){e.printStackTrace();}
}

public static void main(String[] args)
{
    try{
    DateTime today = new DateTime();
    int x = 1;
    map.put("Hello!", x);
    StoreMapInDB(map);
    }catch(IOException ioe){
        System.err.print(ioe);
    }
}
}

错误在main方法的行中是:

map.put("Hello!", x);

它给:

Exception in thread "main" java.lang.NullPointerException
at core.smd.classes.TestOracleMap.main(TestOracleMap.java:61)
 Java Result: 1

Answer 1

好像你永远不会实例化map.你在这里声明

static TreeMap<String, Integer> map;

但是当你在这里使用它仍然null给你NullPointerException.

map.put("Hello!", x);

如果你以前这样做过

map = new TreeMap<String, Integer>();

它应该运行正常.