XML NullPointerException

Programming Questions

davidcool

in Programming Questions • 2 months ago

Hi,

This used to work but now gives a NullPointerException. I can't figure out what's up, but I'm guessing the newer version of Processing (2.0.x) had a syntax change or something??? It's driving me crazy, please help! :-)

Here is the XML file I'm loading:

<?xml version="1.0"?>
<harmonograph version="2.0">
<instance id="0" _d="1414.473" _c="1268.7473" _p="3511.7415" _q="4427.864" _r="2635.5127" _A="0.5578053" _B="0.06687627" _u="0.40685725" _u1="0.05810337" _v="0.00901467" _v1="0.6092852" _R="3.5049737E-4" _S="3.57546E-4" _f="0.052110754" _f1="0.024216956" _g="2.8014755" _g1="1.1454126" _h="0.0023904506" _s="10000.0" _dt="0.01" _sw="0.0020" _c1="236.39992" _c2="245.5904" _c3="199.0" _c4="186.17993" _paper_scale="0.056286596"></instance>
<instance id="1" _d="75.58671" _c="923.0078" _p="2236.305" _q="2558.7473" _r="1439.7762" _A="0.049523104" _B="0.07326763" _u="1.0305866" _u1="0.104935005" _v="0.056840375" _v1="0.61773765" _R="9.204476E-4" _S="7.340446E-4" _f="0.47582477" _f1="6.497495E-4" _g="1.5455143" _g1="0.5479465" _h="0.0019688155" _s="10000.0" _dt="0.01" _sw="0.0020" _c1="233.58257" _c2="114.20393" _c3="161.74295" _c4="228.1528" _paper_scale="0.07382174"></instance>
<instance id="2" _d="4541.5713" _c="3129.408" _p="2517.585" _q="967.66296" _r="715.6475" _A="0.71969116" _B="0.058555778" _u="0.21462521" _u1="0.11627076" _v="0.10193885" _v1="0.6912108" _R="1.9483913E-4" _S="2.0797868E-4" _f="0.43537554" _f1="0.04506056" _g="1.2340766" _g1="2.9522796" _h="0.001092679" _s="10000.0" _dt="0.01" _sw="0.0020" _c1="123.6345" _c2="93.433395" _c3="168.05882" _c4="58.669914" _paper_scale="0.11436498"></instance>
</harmonograph>

Here is the XML function I'm using to process the file:

public int loadXML() {
int xmlObjects = -1;
String xmlFile;
XML xml; // Declare XMLElement object
String path = sketchPath + "/data";
String[] filenames = listFileNames(path);
for (int i = 0; i < filenames.length; i++) {
if (filenames[i].toLowerCase().endsWith(".xml")) {
xmlFile = filenames[i];
xml = loadXML(filenames[i]);
if (xml.getFloat("version") == _version) {
xmlObjects = xml.getChildCount();
pArr = new Harmonograph[xmlObjects];
for (int h = 0; h < xmlObjects; h++) {
XML kid = xml.getChild(h);
pArr[h] = new Harmonograph(h, 1);
pArr[h]._d = kid.getFloat("_d");
pArr[h]._c = kid.getFloat("_c");
pArr[h]._p = kid.getFloat("_p");
pArr[h]._q = kid.getFloat("_q");
pArr[h]._r = kid.getFloat("_r");
pArr[h]._A = kid.getFloat("_A");
pArr[h]._B = kid.getFloat("_B");
pArr[h]._u = kid.getFloat("_u");
pArr[h]._u1 = kid.getFloat("_u1");
pArr[h]._v = kid.getFloat("_v");
pArr[h]._v1 = kid.getFloat("_v1");
pArr[h]._R = kid.getFloat("_R");
pArr[h]._S = kid.getFloat("_S");
pArr[h]._f = kid.getFloat("_f");
pArr[h]._f1 = kid.getFloat("_f1");
pArr[h]._g = kid.getFloat("_g");
pArr[h]._g1 = kid.getFloat("_g1");
pArr[h]._h = kid.getFloat("_h");
pArr[h]._s = kid.getFloat("_s");
pArr[h]._dt = kid.getFloat("_dt");
pArr[h]._sw = kid.getFloat("_sw");
pArr[h]._c1 = kid.getFloat("_c1");
pArr[h]._c2 = kid.getFloat("_c2");
pArr[h]._c3 = kid.getFloat("_c3");
pArr[h]._c4 = kid.getFloat("_c4");
pArr[h]._paper_scale = kid.getFloat("_paper_scale");
// print out variable values
println("Variables generated from XML file '" + xmlFile + "'");
println("Harmonograph Object: " + pArr[h]._id);
println("Stroke color: " + pArr[h]._c1 + "," + pArr[h]._c2 + "," + pArr[h]._c3 + "," + pArr[h]._c4);
println("First x, y: " + pArr[h]._x + "," + pArr[h]._y);
println("Paper scale: " + pArr[h]._paper_scale);
println("d = " + pArr[h]._d);
println("c = " + pArr[h]._c);
println("p = " + pArr[h]._p);
println("q = " + pArr[h]._q);
println("r = " + pArr[h]._r);
println("A = " + pArr[h]._A);
println("B = " + pArr[h]._B);
println("u = " + pArr[h]._u);
println("u1 = " + pArr[h]._u1);
println("v = " + pArr[h]._v);
println("v1 = " + pArr[h]._v1);
println("R = " + pArr[h]._R);
println("S = " + pArr[h]._S);
println("f = " + pArr[h]._f);
println("f1 = " + pArr[h]._f1);
println("g = " + pArr[h]._g);
println("g1 = " + pArr[h]._g1);
println("h = " + pArr[h]._h);
println("");
}
println("Harmonograph Version " + _version);
println("http://www.davidcool.com/");
println("");
} else {
println("****************************************************************************************************");
println("ERROR LOADING XML FILE DATA!!!");
println("Version mismatch!");
println("XML harmonograph version: " + xml.getFloat("version") + " Sketch harmonograph version: " + _version);
println("Be sure that the XML file was generated by this version of the sketch.");
println("Defaulting to random variable generation...");
println("****************************************************************************************************");
println("");
}
}
}
return xmlObjects;
}

Line 18 in the snippet above is highlighted in yellow and seems to be throwing the error. I've combed over this several times and can't seem to figure out what's causing this!

Thanks,

David

Replies(3)

tfguy44

Re: XML NullPointerException

2 months ago

Does your Harmonograph object have a _d data member? Can we see how is it initialized?

PhiLho

Re: XML NullPointerException

2 months ago

xml.getChildCount();

is probably the culprit.

I still have to write a Technical FAQ about this one...

The XML parser went from a semi-custom one (adapted from some simple library) to the official Java one, much more complete and compliant.

One of the main differences is precisely this compliance: the spaces and end-of-line characters between tags are also XML elements, that can be parsed, etc.

So these characters ignored by our eyes when we look at an XML file count as children...

There are several GitHub issues opened against this problem, which is not a bug!

The proper way to parse such XML file is now to get the children named instance and to loop over them. Don't loop blindly over the content of an XML file, get the tags you need to have.

davidcool

Re: XML NullPointerException

2 months ago

@PhiLho

Thanks for getting me going in the right direction, I started poking around and found a workable solution. I used xml.getChildren with a specific tag.

Cheers

public int loadXML() {
int xmlObjects = -1;
String xmlFile;
XML xml; // Declare XMLElement object
String path = sketchPath + "/data";
String[] filenames = listFileNames(path);
for (int i = 0; i < filenames.length; i++) {
if (filenames[i].toLowerCase().endsWith(".xml")) {
xmlFile = filenames[i];
xml = loadXML(filenames[i]);
if (xml.getFloat("version") == _version) {
XML[] xObjects = xml.getChildren("instance");
xmlObjects = xObjects.length;
pArr = new Harmonograph[xObjects.length];
for (int h = 0; h < xObjects.length; h++) {
pArr[h] = new Harmonograph(h, 1);
pArr[h]._d = xObjects[h].getFloat("_d");
pArr[h]._c = xObjects[h].getFloat("_c");
pArr[h]._p = xObjects[h].getFloat("_p");
pArr[h]._q = xObjects[h].getFloat("_q");
pArr[h]._r = xObjects[h].getFloat("_r");
pArr[h]._A = xObjects[h].getFloat("_A");
pArr[h]._B = xObjects[h].getFloat("_B");
pArr[h]._u = xObjects[h].getFloat("_u");
pArr[h]._u1 = xObjects[h].getFloat("_u1");
pArr[h]._v = xObjects[h].getFloat("_v");
pArr[h]._v1 = xObjects[h].getFloat("_v1");
pArr[h]._R = xObjects[h].getFloat("_R");
pArr[h]._S = xObjects[h].getFloat("_S");
pArr[h]._f = xObjects[h].getFloat("_f");
pArr[h]._f1 = xObjects[h].getFloat("_f1");
pArr[h]._g = xObjects[h].getFloat("_g");
pArr[h]._g1 = xObjects[h].getFloat("_g1");
pArr[h]._h = xObjects[h].getFloat("_h");
pArr[h]._s = xObjects[h].getFloat("_s");
pArr[h]._dt = xObjects[h].getFloat("_dt");
pArr[h]._sw = xObjects[h].getFloat("_sw");
pArr[h]._c1 = xObjects[h].getFloat("_c1");
pArr[h]._c2 = xObjects[h].getFloat("_c2");
pArr[h]._c3 = xObjects[h].getFloat("_c3");
pArr[h]._c4 = xObjects[h].getFloat("_c4");
pArr[h]._paper_scale = xObjects[h].getFloat("_paper_scale");
// print out variable values
println("Variables generated from XML file '" + xmlFile + "'");
println("Harmonograph Object: " + pArr[h]._id);
println("Stroke color: " + pArr[h]._c1 + "," + pArr[h]._c2 + "," + pArr[h]._c3 + "," + pArr[h]._c4);
println("First x, y: " + pArr[h]._x + "," + pArr[h]._y);
println("Paper scale: " + pArr[h]._paper_scale);
println("d = " + pArr[h]._d);
println("c = " + pArr[h]._c);
println("p = " + pArr[h]._p);
println("q = " + pArr[h]._q);
println("r = " + pArr[h]._r);
println("A = " + pArr[h]._A);
println("B = " + pArr[h]._B);
println("u = " + pArr[h]._u);
println("u1 = " + pArr[h]._u1);
println("v = " + pArr[h]._v);
println("v1 = " + pArr[h]._v1);
println("R = " + pArr[h]._R);
println("S = " + pArr[h]._S);
println("f = " + pArr[h]._f);
println("f1 = " + pArr[h]._f1);
println("g = " + pArr[h]._g);
println("g1 = " + pArr[h]._g1);
println("h = " + pArr[h]._h);
println("");
}
println("Harmonograph Version " + _version);
println("http://www.davidcool.com/");
println("");
} else {
println("****************************************************************************************************");
println("ERROR LOADING XML FILE DATA!!!");
println("Version mismatch!");
println("XML harmonograph version: " + xml.getFloat("version") + " Sketch harmonograph version: " + _version);
println("Be sure that the XML file was generated by this version of the sketch.");
println("Defaulting to random variable generation...");
println("****************************************************************************************************");
println("");
}
}
}
return xmlObjects;
}

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