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Recursive calculation in Java

I'm trying to solve a calculation problem in Java.
Suppose my data looks as follows:
466,2.0762
468,2.0799
470,2.083
472,2.0863
474,2.09
476,2.0939
478,2.098
It's a list of ordered pairs, in the form of [int],[double]. Each line in my file contains one pair. The file can contain seven to seven thousand of those lines, all of them formatted as plain text.
Each [int] must be subtracted from the [int] one line above and the result written onto another file. The same calculation must be done for every [double]. For example, in the data reported above, the calculation should be:
478-476 -> result to file
476-474 -> result to file
(...)
2.098-2.0939 -> result to file
2.0939-2.09 -> result to file
and so on.
I beg your pardon if this question will look trivial for the vast majority of you, but after weeks trying to solve it, I got nowhere. I also had troubles finding something even remotely similar on this board!
Any help will be appreciated.
Thanks!

Read the file
Build the result
Write to a file
For the 1. task there are already several good answers here, for example try this one: Reading a plain text file in Java.
You see, we are able to read a file line per line. You may build a List<String> by that which contains the lines of your file.
To the 2. task. Let's iterate through all lines and build the result, again a List<String>.
List<String> inputLines = ...
List<String> outputLines = new LinkedList<String>();
int lastInt = 0;
int lastDouble = 0;
boolean firstValue = true;
for (String line : inputLines) {
// Split by ",", then values[0] is the integer and values[1] the double
String[] values = line.split(",");
int currentInt = Integer.parseInt(values[0]);
double currentDouble = Double.parseDouble(values[1]);
if (firstValue) {
// Nothing to compare to on the first run
firstValue = false;
} else {
// Compare to last values and build the result
int diffInt = lastInt - currentInt;
double diffDouble = lastDouble - currentDouble;
String outputLine = diffInt + "," + diffDouble;
outputLines.add(outputLine);
}
// Current values become last values
lastInt = currentInt;
lastDouble = currentDouble;
}
For the 3. task there are again good solutions on SO. You need to iterate through outputLines and save each line in a file: How to create a file and write to a file in Java?

Finding the index of a string with specific requirements?

I'm a bit of a newbie to programming. :P
I'm working with Processing right now to create a table of subjects with their ID, Title and Availability.
I have a 2D array that contains information like this:
units[0][0] = "CAKE100"; //Subject ID
units[1][0] = "Eating Cake And Baking Too"; //Subject Title
units[2][0] = "November"; //Subject Availability
units[0][1] = "TACO204"; //Subject ID
units[1][1] = "Tacos And Other Delicious Things"; //Subject Title
units[2][1] = "April"; //Subject Availability
units[0][2] = "KITC102"; //Subject ID
units[1][2] = "Kitchen Safety"; //Subject Title
units[2][2] = "June"; //Subject Availability
I'm trying to filter through the unit[0][x] section to find the index location of every Subject ID that has "1" in the fourth position of the string.
For example, I want to return [0] [0] and [0] [2], because "CAKE100" and "KITC102" both have "1" in the fourth position.
I've tried to use indexOf or .substring but for some reason I can't figure it out.
EDIT:
Not sure how much help it will be but here's my butchered code:
void checkLevel100() {
for ( int j = 0; j < units.length; j++) {
position = 0;
// position = units[0][j].indexOf("1"); //This returns 4;
if (units[0][j].substring(4) == "1") { //This doesn't run at all, and so it returns 0.
position = j;
}
fill(0);
text(position, width/2, height/2);
}
}
I also did what Kevin Workman suggested. Here is the code for that:
for (int i = 0; i < units.length; i++) {
if(units[0][i] == "TACO204"){ //This results in 1, as expected
location[i] = i;
println(i);
}
Once again, thank you for your time :)

You need to break your problem down into smaller steps.
Step 1: Loop over your 2D array. You might use a nested for loop for this.
To test that this step works, you might just print every element in your 2d array before worrying about any logic.
Step 2: Write an if statement that checks whether the value at that index passes your test.
To test that this step works, you might want to create a separate program that just tests a hardcoded value instead of using arrays.
Step 3: Once you have the first two steps working, then you can save the indexes that pass your test into some kind of data structure. You might us an ArrayList<Integer> for this.
Create a separate example program that just loops over an array without worrying about any logic. Create another separate program that just uses an if statement to test your condition against a hard-coded value. Then if you get stuck on a specific step, you can post a more specific question along with an MCVE. Good luck.

I think it would be simpler for you to store your subject's values as an object of a class. Perhaps store the numerical portion of the ID as an int too? Using a class will enable you to write more human readable code.
public class FoodSubject {
String stringID;
int numID;
String title;
String availability;
public FoodSubject(String stringID, int numID,
String title, String availability) {
this.stringID = stringID;
this.numID = numID;
this.title = title;
this.availability = availability;
}
}
To make a new array of your FoodSubject objects use this code:
FoodSubject[] subjectArray = new FoodSubject[3];
subjectArray[0] = new FoodSubject("CAKE", 100, "Eating Cake And Baking Too", "November");
Access the values like this subjectArray[0].numID
Look into overriding the toString() method in your class to print out all the values of your subject easily. This will help you identify problems in the rest of your code much easier!
If you still want to store the entire ID as a String use the charAt(int index) function to test if the character is a '1'.
This if (units[0][j].substring(4) == "1") { code is incorrect. Look at the String Java documentation for information on what substring does.

JVisualVM HeapDump OQL rendering array inside an Object

I am trying to write a query such as this:
select {r: referrers(f), count:count(referrers(f))}
from com.a.b.myClass f
However, the output doesn't show the actual objects:
{
count = 3.0,
r = [object Object]
}
Removing the Javascript Object notation once again shows referrers normally, but they are no longer compartmentalized. Is there a way to format it inside the Object notation?

So I see that you asked this question a year ago, so I don't know if you still need the answer, but since I was searching around for something similar, I can answer this. The problem is that referrers(f) returns an enumeration and so it doesn't really translate well when you try to put it into your hashmap. I was doing a similar type of analysis where I was trying to find unique char arrays (count the unique combinations of char arrays up to the first 50 characters). What I came up with was this:
var counts = {};
filter(
map(
unique(
map(
filter(heap.objects('char[]'), "it.length > 50"), // filter out strings less than 50 chars in length
function(charArray) { // chop the string at 50 chars and then count the unique combos
var subs = charArray.toString().substr(0,50);
if (! counts[subs]) {
counts[subs] = 1;
} else {
counts[subs] = counts[subs] + 1;
}
return subs;
}
) // map
) // unique
, function(subs) { // map the strings into an array that has the string and the counts of that string
return { string: subs, count: counts[subs] };
}) // map
, "it.count > 5000"); // filter out strings that have counts < 5000
This essentially shows how to take an enumeration (heap.objects('char[]') in this case) and filter it and map it so that you can compute statistics on it. Hope this helps someone.

String naming convention in java

I am currently trying to make a naming convention. The idea behind this is parsing.
Lets say I obtain an xml doc. Everything can be used once, but these 2 in the code below can be submitted several times within the xml document. It could be 1, or simply 100.
This states that ItemNumber and ReceiptType will be grabbed for the first element.
ItemNumber1 = eElement.getElementsByTagName("ItemNumber").item(0).getTextContent();
ReceiptType1 = eElement.getElementsByTagName("ReceiptType").item(0).getTextContent();
This one states that it will grab the second submission if they were in their twice.
ItemNumber2 = eElement.getElementsByTagName("ItemNumber").item(1).getTextContent();
ReceiptType2 = eElement.getElementsByTagName("ReceiptType").item(1).getTextContent();
ItemNumber and ReceiptType must both be submitted together. So if there is 30 ItemNumbers, there must be 30 Receipt Types.
However now I would like to set this in an IF statement to create variables.
I was thinking something along the lines of:
int cnt = 2;
if (eElement.getElementsByTagName("ItemNumber").item(cnt).getTextContent();)
**MAKE VARIABLE**
Then make a loop which adds one to count to see if their is a third or 4th. Now here comes the tricky part..I need them set to a generated variable. Example if ItemNumber 2 existed, it would set it to
String ItemNumber2 = eElement.getElementsByTagName("ItemNumber").item(cnt).getTextContent();
I do not wish to make pre-made variable names as I don't want to code a possible 1000 variables if that 1000 were to happen.
KUDOS for anyone who can help or give tips on just small parts of this as in the naming convention etc. Thanks!

You don't know beforehand how many ItemNumbers and ReceiptTypes you'll get ? Maybe consider using two Lists (java.util.List). Here is an example.
boolean finished = ... ; // true if there is no more item to process
List<String> listItemNumbers = new ArrayList<>();
List<String> listReceiptTypes = new ArrayList<>();
int cnt = 0;
while(!finished) {
String itemNumber = eElement.getElementsByTagName("ItemNumber").item(cnt).getTextContent();
String receiptType = eElement.getElementsByTagName("ReceiptType").item(cnt).getTextContent();
listItemNumbers.add(itemNumber);
listReceiptTypes.add(receiptType);
++cnt;
// update 'finished' (to test if there are remaining itemNumbers to process)
}
// use them :
int indexYouNeed = 32; // for example
String itemNumber = listItemNumbers.get(indexYouNeed); // index start from 0
String receiptType = listReceiptTypes.get(indexYouNeed);

Protobuf in java : Uid.Lists from Accumulo Values go in but they don't come out

I am attempting to write and read Uids from Accumulo Value (key,Value) into Uid.List using protobuf.
Specifically:
org.apache.accumulo.examples.wikisearch.protobuf.Uid;import org.apache.accumulo.examples.wikisearch.protobuf.Uid.List.Builder
I use the following code to write Uid.List where I declare UidListCount as #of uids in List Cseq:
Builder uidBuilder = Uid.List.newBuilder();
uidBuilder.setIGNORE(false);
for String entry : seq){
uidBuilder.addUID(entry);
}
Uid.List uidList = uidBuilder.build();
Value newAccumuloValue = new Value(uidList.toByteArray());
This seems to work fine.
When I Try to read the Uid.List out of accumulo value,where value is a protobuf Uid.List, its a no-go:
byte[] byteVal = value.getBytes; //retrieving Accumulo Value containing Uid.List
Uid.List uids= Uid.List.parseFrom(byteVal);
while (counter <= counter){
String uidStr = uids.getUID(counter).toString();
system.out.println(uidStr);
}
I keep getting "tag errors"
I would really like to understand how to read out what goes in.
Thanks!

I would suggest changing the second bit of code to something along the lines of:
byte[] byteVal = value.getBytes;
Uid.List uids= Uid.List.parseFrom(byteVal);
int count = uids.getUIDCount();
for (int i = 0; i< count; i++){
String uidStr = uids.getUID(i).toString();
system.out.println(uidStr);
}
This code does work as long as the UIDs in your list are properly cleaned before the list is built by protobuf. If you have characters within the data (such as unicode nulls) that are used by protobuf as part of the list format then, when parsing the data back out, it is going to break because data characters will be recognized as format characters that don't properly match the data schema. I would start by taking a look at your data and ensuring that it meets data quality and cleanliness standards for what you are trying to achieve.