useing NULL as Integer parameter in Java

Question

I have a problem with useing NULL as Integer parameter.

I have 3 classes which extend each other:

//1st
public class StandardTableIntId {
    ...

    protected MethodAnswer changeField(String field, Integer value) {
    DBConnection dbc = new DBConnection();
    Connection con = dbc.getConnection();
    try {
        PreparedStatement st = con.prepareStatement("UPDATE " + this.tableName + " SET " + field + " = ? WHERE id = ?");
        st.setInt(1, value);
        st.setInt(2, this.id);
        st.executeUpdate();
        return MethodAnswer.OK;
    } catch (SQLException ex) {
        log.info("SQLException. Class: StandardTableIntId. Method: changeField(String field, String value). Parameters: table='" + tableName + "' id='" + id + "' field='" + field + "' value='" + value + "'");
        return MethodAnswer.DB_EXCEPTION;
    }
    finally
    {
        dbc.closeConnection();
    }   
    }
    protected MethodAnswer changeField(String field, String value) {
    ...
    st.setString(1, value);
    ...}
    protected MethodAnswer changeField(String field, Long value) {
    ...
    st.setLong(1, value);
    ...}
    protected MethodAnswer changeField(String field, boolean value) {
    ...
    st.setBoolean(1, value);
    ...}
    ...
}   


//2nd
public class StandardTableIntIdTimed extends StandardTableIntId{...}

//3rd   
public class Company extends StandardTableIntIdTimed {
    ...
    public MethodAnswer setMainIncomeBankAccountId(Integer value) {
        MethodAnswer ans;
// !!! Code crashes in next command (if value==null). Eclipse just said: "Source not found." in debugging mode.
            ans = changeField("mainIncomeBaId", value); 
        return ans;
    }
    ...
}

Code crashes in line that marked "//!!!" comment. It happens when "value" is equals to null.

In the same methods but String or Timestamp params is everithing OK:

public MethodAnswer setPostAddress(String postAddress) {
    MethodAnswer ans;
    ans = changeField("postAddress", value); 
    return ans;
}
public MethodAnswer setDateTimeBegin(Timestamp value) {
    MethodAnswer ans;
    ans = changeField("DateTimeBegin", value); 
    return ans;
}

Can't understend what's happening here and how to fix it.

Please show a short but complete program demonstrating the problem. — Jon Skeet
– Jon Skeet, Commented Oct 23, 2012 at 14:07
Add changeField(...) code. All methods do the same thing put one value in DB. It's just different values String/Integer/etc — vdshb
– vdshb, Commented Oct 23, 2012 at 15:03

Simon Forsberg · Accepted Answer · 2012-10-23 14:09:52Z

1

Ok, I'm guessing a bit here, but...

protected MethodAnswer changeField(String field, Integer value)

If you within this method convert the value parameter to an int, and value is NULL, then you will get a NullPointerException. The solution: Check if value is NULL before converting it to int.

answered Oct 23, 2012 at 14:09

Simon Forsberg

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Comments

Averroes · Accepted Answer · 2012-10-23 14:16:35Z

0

You probably are doing some calculations using value. Since value is null the application throws a NullPointerException

EG:

public void test(Integer n){
  System.out.println(n + 4);
}

With the code above, the following code will throw a NullPointerException

test(null)

edited Oct 23, 2012 at 14:16

answered Oct 23, 2012 at 14:10

Averroes

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