Re: [netcdf-java] java.lang.NullPointerException at ucar.nc2.NetcdfFileWriter.write(NetcdfFileWriter.java:939)

Dear Beáta,

I have answered to you at StackOverflow:

You are declaring your variables twice, once as static:

  public static Variable time;

and other in the local scope of your switch:

  Variable time = ncfile.addVariable(...);

and therefore you are "losing" the initialized Object in the local scope.
Replace the local declaration by just the assigning the initialized Object to the static variable declaration: 

  time = ncfile.addVariable(...);

Regards

Antonio S. Cofiño

P.S.:

I have already answered to your question at StackOverflow:

https://stackoverflow.com/questions/50964120/how-can-i-initialize-the-netcdf-varables-as-global-variables-to-avoid-java-lang


On 22/06/18 08:43, Beáta Szabó-Takács wrote:


Dear All,
I would like to write a netCDF4 file in Java based on https://www.unidata.ucar.edu/software/thredds/current/netcdf-java/tutorial/NetcdfWriting.html. I have a lot of variables and I would like to select just some and write only them to netcdf file. I tried to solve this by the the following way: 

publicclassJavaDB{

publicstaticVariabletime;

publicstaticVariablecloud_1st;

publicstaticVariablecloud_2nd;

publicstaticVariablecloud_3th;

publicstaticVariablecloud_4th;

publicstaticVariablecloud_5th;

publicstaticVariableLayer_1st;

publicstaticVariableLayer_2nd;

publicstaticVariableLayer_3th;

publicstaticVariableLayer_4th;

publicstaticVariableLayer_5th;

publicstaticVariableCBN;
publicstaticvoidgetDataNC(Stringlocation, ArrayList<Integer> Values) throwsException{ 

Stringversion = System.getProperty("java.version");
NetcdfFileWriterncfile = NetcdfFileWriter.createNew(NetcdfFileWriter.Version.netcdf4, location, null); 

// add dimensions

DimensionheightDim = ncfile.addDimension(null,"height",1539);

DimensiontimeDim = ncfile.addUnlimitedDimension("time");

//define variables

for(intk=0; k<Values.size(); k++){

switch(Values.get(k)){
case1: Variabletime = ncfile.addVariable(null, "time", DataType.DOUBLE,"time"); 

time.addAttribute( newAttribute("units", "days since 1970-01-01"));

break;
case2: Variablecloud_1st = ncfile.addVariable(null,"cloud_1st", DataType.INT,"time");
cloud_1st.addAttribute( newAttribute("long_name", "cloud amount in 1st layer1")); 

             cloud_1st.addAttribute( newAttribute("units", "octa"));

cloud_1st.addAttribute(newAttribute("_FillValue",-9999));

cloud_1st.addAttribute(newAttribute("Vertical Visibility",9));

         cloud_1st.addAttribute(newAttribute("No enough data",99));

break;
case3: Variablecloud_2nd = ncfile.addVariable(null,"cloud_2nd", DataType.INT,"time");
cloud_2nd.addAttribute( newAttribute("long_name", "cloud amount in 2nd layer")); 

cloud_2nd.addAttribute( newAttribute("units", "octa"));

cloud_2nd.addAttribute(newAttribute("_FillValue",-9999));

cloud_2nd.addAttribute(newAttribute("Vertical Visibility",9));

cloud_2nd.addAttribute(newAttribute("No enough data",99));

break;
case4: Variablecloud_3th = ncfile.addVariable(null,"cloud_3th", DataType.INT,"time");
cloud_3th.addAttribute( newAttribute("long_name", "cloud amount in 3th layer")); 

cloud_3th.addAttribute( newAttribute("units", "octa"));

cloud_3th.addAttribute(newAttribute("_FillValue",-9999));

cloud_3th.addAttribute(newAttribute("Vertical Visibility",9));

cloud_3th.addAttribute(newAttribute("No enough data",99));

break;
case5: Variablecloud_4th = ncfile.addVariable(null, "cloud_4th", DataType.INT, "time");
cloud_4th.addAttribute( newAttribute("long_name", "cloud amount in 4th layer")); 

cloud_4th.addAttribute( newAttribute("units", "octa"));

cloud_4th.addAttribute(newAttribute("_FillValue",-9999));

cloud_4th.addAttribute(newAttribute("Vertical Visibility", 9));

cloud_4th.addAttribute(newAttribute("No enough data",99));

break;
case6: Variablecloud_5th = ncfile.addVariable(null, "cloud_5th", DataType.INT, "time");
cloud_5th.addAttribute( newAttribute("long_name", "cloud amount in 5th layer")); 

cloud_5th.addAttribute( newAttribute("units", "octa"));

cloud_5th.addAttribute(newAttribute("_FillValue",-9999));

cloud_5th.addAttribute(newAttribute("Vertical Visibility",9));

cloud_5th.addAttribute(newAttribute("no enough data",99));

break;
case7: VariableLayer_1st= ncfile.addVariable(null,"Layer_1st",DataType.INT,"time");
Layer_1st.addAttribute(newAttribute("long_name", "1st cloud layer height")); 

Layer_1st.addAttribute(newAttribute("units","meter"));

Layer_1st.addAttribute(newAttribute("_FillValue",-9999));

break;
case8: VariableLayer_2nd= ncfile.addVariable(null,"Layer_2nd",DataType.INT,"time");
Layer_2nd.addAttribute(newAttribute("long_name", "2nd cloud layer height")); 

Layer_2nd.addAttribute(newAttribute("units","meter"));

Layer_2nd.addAttribute(newAttribute("_FillValue",-9999));

break;
case9: VariableLayer_3th= ncfile.addVariable(null,"Layer_3th",DataType.INT,"time");
Layer_3th.addAttribute(newAttribute("long_name", "3th cloud layer height")); 

Layer_3th.addAttribute(newAttribute("units","meter"));

Layer_3th.addAttribute(newAttribute("_FillValue",-9999));

break;
case10: VariableLayer_4th= ncfile.addVariable(null,"Layer_4th",DataType.INT,"time");
Layer_4th.addAttribute(newAttribute("long_name", "4th cloud layer height")); 

Layer_4th.addAttribute(newAttribute("units","meter"));

Layer_4th.addAttribute(newAttribute("_FillValue",-9999));

break;
case11: VariableLayer_5th= ncfile.addVariable(null,"Layer_5th",DataType.INT,"time");
Layer_5th.addAttribute(newAttribute("long_name", "5th cloud layer height")); 

Layer_5th.addAttribute(newAttribute("units","meter"));

Layer_5th.addAttribute(newAttribute("_FillValue",-9999));

break;

case12: VariableCBN = ncfile.addVariable(null,"CBN",DataType.INT,"time");

CBN.addAttribute(newAttribute("long_name","cloud base number"));

CBN.addAttribute(newAttribute("units", "number"));

CBN.addAttribute(newAttribute("no significant backscatter",0));

CBN.addAttribute(newAttribute("obscuration but no cloud",4));

CBN.addAttribute(newAttribute("transparent obscuration",5));

CBN.addAttribute(newAttribute("_FillValue",-9));

break;

}

}

ncfile.create();

try{

ArrayDouble.D1 timeData = newArrayDouble.D1(countLinesResult);

ArrayInt.D1 cloudL1Data = newArrayInt.D1(countLinesResult);

Indexima = cloudL1Data.getIndex();

ArrayInt.D1 cloudL2Data = newArrayInt.D1(countLinesResult);

ArrayInt.D1 cloudL3Data = newArrayInt.D1(countLinesResult);

ArrayInt.D1 cloudL4Data = newArrayInt.D1(countLinesResult);

ArrayInt.D1 cloudL5Data = newArrayInt.D1(countLinesResult);

ArrayInt.D1 cLayer1Data = newArrayInt.D1(countLinesResult);

ArrayInt.D1 cLayer2Data = newArrayInt.D1(countLinesResult);

ArrayInt.D1 cLayer3Data = newArrayInt.D1(countLinesResult);

ArrayInt.D1 cLayer4Data = newArrayInt.D1(countLinesResult);

ArrayInt.D1 cLayer5Data = newArrayInt.D1(countLinesResult);

ArrayInt.D1 CBNData= newArrayInt.D1(countLinesResult);

for(inttimeIdx = 0; timeIdx < countLinesResult;timeIdx++){

for(intk=0; k<Values.size(); k++){

// System.out.println(Values.get(k));

if(Values.get(k)==1){

timeData.setDouble(timeIdx,tdate.get(timeIdx));}

if(Values.get(k)==2){

cloudL1Data.setInt(ima.set(timeIdx), cloud_layer_1st.get(timeIdx));}

if(Values.get(k)==3){

cloudL2Data.setInt(ima.set(timeIdx), cloud_layer_2nd.get(timeIdx));}

if(Values.get(k)==4){

cloudL3Data.setInt(ima.set(timeIdx), cloud_layer_3th.get(timeIdx));}

if(Values.get(k)==5){

cloudL4Data.setInt(ima.set(timeIdx), cloud_layer_4th.get(timeIdx));}

if(Values.get(k)==6){

cloudL5Data.setInt(ima.set(timeIdx), cloud_layer_5th.get(timeIdx));}

if(Values.get(k)==7){
                                cLayer1Data.setInt(ima.set(timeIdx), LayerC_1st.get(timeIdx));} 

if(Values.get(k)==8){

cLayer2Data.setInt(ima.set(timeIdx), LayerC_2nd.get(timeIdx));}

if(Values.get(k)==9){

 cLayer3Data.setInt(ima.set(timeIdx), LayerC_3th.get(timeIdx));}

if(Values.get(k)==10){

cLayer4Data.setInt(ima.set(timeIdx), LayerC_4th.get(timeIdx));}

if(Values.get(k)==11){

cLayer5Data.setInt(ima.set(timeIdx), LayerC_5th.get(timeIdx));}

if(Values.get(k)==12){

CBNData.setInt(ima.set(timeIdx),nbcb.get(timeIdx));}

}

}

// write the data into netCDF file

for(intk=0; k<Values.size(); k++){

if(Values.get(k)==1){

ncfile.write(time, timeData);}

if(Values.get(k)==2){

ncfile.write(cloud_1st, cloudL1Data);}

if(Values.get(k)==3){

ncfile.write(cloud_2nd, cloudL2Data);}

if(Values.get(k)==4){

ncfile.write(cloud_3th, cloudL3Data);}

if(Values.get(k)==5){

ncfile.write(cloud_4th, cloudL4Data);}

if(Values.get(k)==6){

ncfile.write(cloud_5th, cloudL5Data);}

if(Values.get(k)==7){

ncfile.write(Layer_1st, cLayer1Data);}

if(Values.get(k)==8){

ncfile.write(Layer_2nd, cLayer2Data);}

if(Values.get(k)==9){

ncfile.write(Layer_3th, cLayer3Data);}

if(Values.get(k)==10){

ncfile.write(Layer_4th, cLayer4Data);}

if(Values.get(k)==11){

ncfile.write(Layer_5th, cLayer5Data);}

if(Values.get(k)==12){

ncfile.write(CBN,CBNData);}

}

}catch(Exceptione){

e.printStackTrace();}

finally{

try{

ncfile.close();

}catch(IOExceptionex){

ex.printStackTrace();

}

}
But after I run the code I get java.lang.NullPointerException at ucar.nc2.NetcdfFileWriter.write(NetcdfFileWriter.java:939). I tried to solve it with define global variables size e.g public static Variable time = new Variable(); but it is not possible. Could you please informe me how I should fix this issue? 

Thank you for your help in adavnce!

Best regards,

Beata



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