Add String Variable To List (Keep Adding To List)

Question

Question 1:

I have a function that is called every time I get a new Lat Long value, I would like to add these Lat Long values to a list but every time I get a new value the list is over written with the last value (not appended).

My code (with only latitude)

    public void getDistance() {

    List<String> list = new ArrayList<String>();
    list.add(latitudeString);

    System.out.println("list: "+list);  
}

Question 2:

Once I have values in the list (which will increase as values change) I would like to get the last two values everytime the list changes and perform some function (get distance between last two Lat Long values in list and so on..)

every time I get a new value the list is over written that is not so weird considering you remake the list every time — Tim
– Tim, Commented Jul 31, 2015 at 13:20

Glorfindel · Accepted Answer · 2015-07-31 13:20:20Z

3

Every time you call

List<String> list = new ArrayList<String>();

a new list will be generated. You need to declare it as a private field in the class (outside the method):

private List<String> list = new ArrayList<String>();

If you want to do calculations though, you need to store them as Doubles, not Strings. That would mean your code will be something like this:

private List<Double> latitudes = new ArrayList<Double>();
private List<Double> longitudes = new ArrayList<Double>();

public void getDistance() {

    // get lat & lon

    Double latitude = Double.parseDouble(latitudeString);
    Double longitude = Double.parseDouble(longitudeString);

    if (latitudes.size() > 0) {
        Double lastLatitude = latitudes.get(latitudes.size() - 1);
        Double lastLongitude = longitudes.get(longitudes.size() - 1);
        // do your calculations
    }

    latitudes.add(latitude);
    longitudes.add(longitude);

}

answered Jul 31, 2015 at 13:20

Glorfindel

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1 Comment

user5174952 Over a year ago

Thank you, I can get old and new with: // do your calculations System.out.println("latitude NEW: " +latitudeString); System.out.println("Latitude OLD: " +latitudes.get(latitudes.size() -1));

Nishant · Accepted Answer · 2015-07-31 13:21:39Z

1

List<String> list = new ArrayList<String>();
public void getDistance() {
list.add(latitudeString);
System.out.println("list: "+list);  
}

You should instaniate your list only once in the starting.

answered Jul 31, 2015 at 13:21

Nishant

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Comments

Nikhil Verma · Accepted Answer · 2015-07-31 13:28:25Z

1

Do it like :

List<String> list = new ArrayList<String>();//declare it outside the method
public void getDistance() {
list.add(latitudeString);

System.out.println("list: "+list);  
}

For the second ques:

    List<String> list = new ArrayList<>();
    int size = list.size();
    String[] data = new String[2];
    data[0] = list.get(size - 2);//2nd to last
    data[1] = list.get(size - 1);//last

answered Jul 31, 2015 at 13:28

Nikhil Verma

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Comments

deezy · Accepted Answer · 2015-07-31 13:35:01Z

0

You will need to declare a class member instead of creating a new local list everytime you call getDistance(). Also, since the list will store latitude and longitude information, I suggested you use double instead of String.

Move the declaration of list to the beginning of the class, and change the type of list and latitudeString to double:

class Class1 {
    List<double> list = new ArrayList<double>();
    ...
    public void getDistance() {
        list.add(latitudeString /*should be a double*/);
        ...
    }
}

Get the last two values using the get() and size() methods:

double value1 = list.get(list.size() - 1); //last value
double value2 = list.get(list.size() - 2); //second-to-last value

edited Jul 31, 2015 at 13:35

answered Jul 31, 2015 at 13:24

deezy

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Comments

Adarsh Yadav · Accepted Answer · 2015-07-31 13:25:16Z

-1

1- You should instantiate your list only once in the starting.

List<String> list = new ArrayList<String>();
public void getDistance() {
list.add(latitudeString);
System.out.println("list: "+list);  
}

2-You will easily get last two items using list.size()-1{your last item} and list.size()-2{Your second last item}.

answered Jul 31, 2015 at 13:25

Adarsh Yadav

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