Data is covered by latter data

Hi everyone
I want to add some data to an ArrayList array, but the latter data just covers the former one, while the size of the array is growing (I learned Java for 4 months by myself and did not take any data structure courses in my college...)
here is the code (they are in the same class):
ArrayList<ArrayList<ArrayList<Double>>> all = new ArrayList<ArrayList<ArrayList<Double>>>();
ArrayList<ArrayList<Double>> calcOutput(ArrayList<ArrayList<Double>> input) throws Exception {
ArrayList<ArrayList<Double>> out = new ArrayList<ArrayList<Double>>();
//calculation;
return out;
}
void allfire(ArrayList<ArrayList<ArrayList<Double>>> tch) throws Exception {
for (int p = 0; p < tch.size(); p++) {
all.add(calcOutput(tch.get(p)));
}
it happens that for p=1 or 2 or else, data in all is always changed to the last data added into all
how does this happen and how to solve it?
Thanks very much

sounds like your are recreating your ArrayList<....<Double> >> somewhere down the line. can you post more of the code? Do you need a three dimensional ArrayList of ArrayList?

Are you sure you need such monsters:
ArrayList<ArrayList<ArrayList<Double>>> all = new ArrayList<ArrayList<ArrayList<Double>>>(); ? :D

My codes is boring in that I have no idea about data structure and object-oriented idea and made it a mess
public class Network {
ArrayList<ArrayList<ArrayList<Double>>> all = new ArrayList<ArrayList<ArrayList<Double>>>();
double[] weight;
ArrayList<ArrayList<Double>> calcOutput(ArrayList<ArrayList<Double>> input) throws Exception {
ArrayList<ArrayList<Double>> out = new ArrayList<ArrayList<Double>>();
//calculate with parameter weight[] and add the data into out
//weight[] will be changed in allfire method
return out;
}//end of calcOutput method
void allfire(ArrayList<ArrayList<ArrayList<Double>>> tch) throws Exception {
for (int pattern = 0; pattern < tch.size(); pattern++) {
boolean test = true;
while(test){// loop until the result(out) is perfect
// calc out
ArrayList<ArrayList<Double>> out = new ArrayList<ArrayList<Double>>();
out = calcOutput(tch.get(pattern));
//if the result(out) is not perfect, change parameter(weight[]) for a better result(a better out)
}//end of loop while
}//end of loop for
//weight[] is good enough to make perfect out for all patterns
//calculate out with this weight[] and add the data into all
all.clear();
for (int p = 0; p < tch.size(); p++) {
all.add(calcOutput(tch.get(p)));
}
}//end of allfire method
}//end of class

for example
for p=0 add [[3.0],[3.2,3.3]] into all
for p=1 add [[4.2,5.3]] into all
then data in all turns out to be[[[4.2,5.3]],[[4.2,5.3]]] which should be [[[3.0],[3.2,3.3]],[[4.2,5.3]]]
seems that for each calcOutput(tch.get(p)),it is the data in the memory changed so that the former data is also changed

Do you have code to test your program? I don't see a main() method or any calls to your methods.