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How do I store this data in Java?

I want a dictionary of values. The keys are all strings. Each key corresponds with some sort of list of strings. How do I make a list of strings for each key and update that accordingly? I'll explain:
I have a loop that is reading lines of a word list. The words are then converted into a string code and set as keys in the dictionary. Here is an example of the string code/word relationship.
123, [the]
456, [dog]
328, [bug]
...
However, my program keeps looping through the word list and eventually will run into a word with the same code as "the", but maybe a different word, lets say "cat". So I want the list to look like:
123, [the, cat]
456, [dog]
...
How do I get it to make an arraylist for every key that I can then add to on the fly when needed? My end goal is to be able to print out the list of words in that list for a called code (.get())

You can make a HashMap. In your case
HashMap<Integer, ArrayList<String>> works fine.

Like it has already been said, a MultiMap seems to be what you need. Guava that was already suggested and it's a good option. There is also and implementation from commons-collections you can use.
From commons-collections documentation:
MultiValuedMap<K, String> map = new MultiValuedHashMap<K, String>();
map.put(key, "A");
map.put(key, "B");
map.put(key, "C");
Collection<String> coll = map.get(key); // returns ["A", "B", "C"]
You can always implement your own MultiMap if you don't want to use an external library. Use a HashMap<String,List<String>> to store your values and wrap it with your own put, get and whatever other methods you see fit.

It sounds like you want a Multimap from the Guava library.
You can also go the route of using a Map<Integer, List<String>>, but then you will need to manually handle the case where the list is null (probably just allocate a new list in that case).

You can use a HashMap that links each id to a list of strings:
Map<String, List<String>> dictionary = new HashMap<String,List<String>>();
Now let's say you read two Strings: id and word . To add them to your dictionary, you can first verify if your id has already been read (using the containsKey() method)- in which case you just append the word to the list corresponding to that id - or, if this is not the case, you create a new list with this word:
//If the list already exists...
if(dictionary.containsKey(id)) {
List<String> appended = dictionary.get(id);
appended.add(word); //We add a new word to our current list
dictionary.remove(id); //We update the map by first removing the old list
dictionary.put(id, appended); //and then appending the new one
} else {
//Otherwise we create a new list for that id
List<String> newList = new ArrayList<String>();
newList.add(word);
dictionary.put(id, newList);
}
Then whenever you want to retrieve your list of strings for a certain id you can simply use dictionary.get(id);
You can find more information on HashMaps on the Java documentation

I assumed you didn't want repeats in your list so I used Set instead.
Map<String,Set<String>> mapToSet = new HashMap<>();
List<String []>keyvals = Arrays.asList(new String[][]{{"123","the"},{"123","cat"}});
for(String kv[] : keyvals) {
Set<String> s = mapToSet.get(kv[0]);
if(null == s) {
s = new HashSet<String>();
}
s.add(kv[1]);
mapToSet.put(kv[0], s);
}

How to make ArrayList that work as two dimentional array in java?

I want to make arrayList object in java that work as two dimentional array. My question is how can we access value from specific dimention from arrayList.
in two dimentional array, if i want to access value then it can be as m[i][j].
But in arraylist how can i do that ?

You mean something like a List in a List??
May be something like...
List<List<...>> twoDList = new ArrayList<>();
i want to make a List, in which each List key contains another List inside it
It should more like you want some kind of Map, which is basically a key/value pair.
Map<String, List<String>> mapValues = new HashMap<>(25);
List<String> listOfValues = ...;
//...
mapValues.put("A unique key for this list", listOfValues);
//...
List<String> thatListOfValues = mapValues.get("A unique key for this list");

List<List<Integer>> list = new ArrayList<List<Integer>>();
list.add(new ArrayList<Integer>());
list.add(new ArrayList<Integer>());
list.get(0).add(5);
list.get(1).add(6);
for(List<Integer> listiter : list)
{
for(Integer integer : listiter)
{
System.out.println("" + integer);
}
}
This way you can get the items like
list.get(1).get(0); //second dimension list -> integer
EDIT:
Although it is true that you can use a Map if you are trying to use numeric indices for example for each list, like so:
Map<Integer, List<YourObject>> map = new HashMap<Integer, List<YourObject>>();
map.put(0, new ArrayList<YourObject>());
map.put(5, new ArrayList<YourObject>());
map.get(0).add(new YourObject("Hello"));
map.get(5).add(new YourObject("World"));
for(Integer integer : map.keySet())
{
for(YourObject yourObject : map.get(integer))
{
yourObject.print(); //example method
System.out.println(" ");
}
}
Although even then the accessing of Lists would be the same as before,
map.get(0).get(1); //List -> value at index
Obviously you don't need to use Integers as the generic type parameter, that's just a placeholder type.

The solution like List<List<..>> is slow then you should use one dimention array like
// Two dimentions: m and n
List<String> arr = new ArrayList<String>(m*n);
for (int i=0; i< m; ++i) {
for (int j=0; j<n; ++j) {
String str=arr.get(i*n + j);
//You code here
}
}

Memory is an important consideration here.
It can be acceptable to model a 2D (or higher dimension) array using a 1D container. (This is how the VARIANT SAFEARRAY of Microsoft's COM works.) But, consider this carefully if the number of elements is large; especially if the container allocates a contiguous memory block. Using something like List<List<... will model a jagged-edged matrix and can fragment your memory.
With the 1D approach, you can use the get(index) method on the ArrayList appropriately transformed:
Given the (i)th row and (j)th column, transform using index = i * rows + j where rows is the number of rows in your matrix.

An arraylist is not an object to make a 2 dimentional arrays. However you can use it anyway :
You can use :
new ArrayList<ArrayList<Object>>; //or
new ArrayList<Object[]>;
But you should implement your own matrix class because you will probably have some check to do and a function get(int row, int column) would be cool

Also consider Table collection provided by Google Guava library. ArrayTable is an implementation based on 2D array.

You cane define like this
1>
List<Object[]> list = new ArrayList<Object[]>();
Fetching
list.get(i)[j];
2>
List<Map<Integer,Object>> list = new ArrayList<Map<Integer,Object>>();
Fetching
list.get(i).get(j);

Get number of distinct elements in a sorted array [duplicate]

This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Java - Distinct List of Objects
i have a sorted array of huge size (around 3000 strings) ,
i need to create an object for each distinct string ,
therefore i need create an array of objects with the size equal to distinct strings in the original array.
any suggestions?
Thanks

Well, if you need the distinct elements and not just the number, you may use a Set.
A Set is:
A collection that contains no duplicate elements.
You keep adding your elements to the set, and then just look at what the set contains.
Something similar to this:
public static String[] getDistinct(String[] input) {
Set<String> distinct = new HashSet<String>();
for(String element : input) {
distinct.add(element);
}
return distinct.toArray(new String[0]);
}
Usage:
String[] input = new String[] {"a", "b", "a", "c", "a", "b", "d"};
String[] distinct = getDistinct(input);
for(String element : distinct) {
System.out.println(element);
}
Result:
d b c a
Note that the order of the elements may not be preserved.
To find the number of the distinct elements, use:
getDistinct(input).length

pseudo code:
previous = Null
sum_size = 0
for (String current: yourarray) {
if (!current.equals(previous)) {
sum_size += current.size()
}
previous = current
}
sum_size is the added size of distinct elements in your array.

I think a Set is what you're looking for.

How to get content of HashMap's looping on java in Android?

I have this :
Map<Integer, String[]> strs = new HashMap<Integer, String[]>();
for (int population = 0 ; population < 20 ; population++) {
strs.put(0, morning_food);
strs.put(1, snack1_food);
strs.put(2, lunch_food);
strs.put(3, snack2_food);
strs.put(4, nite_food);
for (String[] value : strs.values()) {
for (String val : value) {
Log.d("", val);
}
}
}
this will display the content of strs for 20 times, how can I get first strs, or fourteenth strs or else? I have tried save it to array, but it always display the last strs whatever index I want, any solution? Thx

When you use Map.put it will override any value that has already been associated with the key. When you call Map.put(0, ...) 20 times, you still only have one value associated with the key 0, the most recent value passed to put.
If you need to store 20 distinct values associated with a single key, use Guava's Multimap.
Multimap

use LinkedHashMap if you want to loop through it in a set order

Java - Optimize finding a string in a list

I have an ArrayList of objects where each object contains a string 'word' and a date. I need to check to see if the date has passed for a list of 500 words. The ArrayList could contain up to a million words and dates. The dates I store as integers, so the problem I have is attempting to find the word I am looking for in the ArrayList.
Is there a way to make this faster? In python I have a dict and mWords['foo'] is a simple lookup without looping through the whole 1 million items in the mWords array. Is there something like this in java?
for (int i = 0; i < mWords.size(); i++) {
if ( word == mWords.get(i).word ) {
return mWords.get(i);
}
}

If the words are unique then use HashMap. I mean, {"a", 1}, {"b", 2}
Map<String, Integer> wordsAndDates = new HashMap<String, Integer>();
wordsAndDates.put("a", 1);
wordsAndDates.put("b", 2);
and wordsAndDates.get("a") return 1
If not you shouldn't use HashMap because it overrides previous value. I mean
wordsAndDates.put("a", 1);
wordsAndDates.put("b", 2);
wordsAndDates.put("a", 3);
and wordsAndDates.get("a") return 3
In such case you can use ArrayList and search in it

If you're not stuck with an ArrayList you should use some kind of hash based data structure. In this case it seems like a HashMap should fit nicely (it's pretty close to python's dict). This will give you an O(1) lookup time (compared to your current method of linear search).

You want to use a Map in Java
Map<String,Integer> mWords = new HashMap<String, Integer>();
mWords.put ("foo", 112345);

What about Collections.binarySearch() (NB: the list must be sorted) if ou are stuck with the ArrayList