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Sorting a list after another one in Java

I need some help regarding list sorting. So, I have two lists, one which contains entities of type Sarcina(int Id,String desc) (lets call it ls1), and one which contains integers (lets call it ls2). Both lists have the same size. I am trying to sort both of them at the same time in descending order, interchanging the elements from the same positions in the both lists.
So, if I have ls1(Sarcina1,Sarcina2,Sarcina3) and ls2(3,5,4), and I sort ls2 as (5,4,3), I want to have in ls1 sorted as (Sarcina2,Sarcina3,Sarcina1).
Thank you.

You can use Treemap, Which maintains the sorted keys. Here you want to sort your Integers, so add them as keys and add your strings as values of a Treemap. It'll automatically sort it. So try someting like following:
TreeMap tm = new TreeMap();
// Put elements to the map
//Here "your_integer" is key and "your_string" is value in our Treemap
tm.put("your_integer","your_string");
tm.put("your_integer","your_string");
now tm is what you want. which has strings sorted according to your integers.

2 Dimentional array with Hash-map

Is there a way to put a 2d array into a Hash map setup?
Example of the array would be two strings {"John", "red"},
{"George", "blue}
And I would want red to correspond to john etc.
I know I can use a nested loop to go through every item in the 2d array but how would then set it up to add them to the hash-map
hashMap.put("John", "red");

Assuming every array has 2 items in the form of {Name, Color}, you can just iterate over it
for(String[] combo : some2DArray){
someHashMap.Put(combo[0], combo[1]); // Or swap them, depending on what you
// want to be the key and the value
}
If you want to avoid the possibility of removing data because you happen to have two people with the same name there are a few approaches you can take:
Keep the old data
Keep the new data
Assign the new data to a new key
Combine the data in the same key
Keep the old data
Perform a check before using HashMap#put and see if the key already exists.
Only add the data if it doesn't exist yet.
Keep the new data
Use the current code, it will overwrite the old value.
Assign the new data to a new key
Create a new key based on your own rules and insert that.
Combine the data in the same key
Define your HashMap as HashMap<String, List<String>> and add the values to the list.

How about implementing a Pair class, so you can use HashMap<Pair<String,String>> ?
EDIT: Might be that I misunderstood your question, is that what yoe were asking?

Creating a HashMap as an index for title keywords to improve search efficiency

I have a custom class Disks which stores various information of CDs such as their Title, Length, Artist etc. These Disks objects are stored in an ArrayList which can only have elements of Disks added. I am using a method to search for these objects based on matching their title. It takes a user input and then goes through each element of the list and compares the user keyword and the Title of the CD. If it is a complete match, its information is then returned to the user.
I want to change this search mechanization slightly by incorporating a HashMap. I am looking to tokenize each Disks Title and then create a mapping entry for the keyword.
Here is an example: The word "Cars" appears in the titles of the ArrayList elements at position 0,5,7. I want to be able to create a mapping entry for "Cars" which will be a list [0,5,7]. If another element is added to the ArrayList at position 10 with "Cars" in the title, how would I amend the old mapping entry so the new list would be [0,5,7,10]?
In the end I want the user to search for title keywords “Loud Cars”. I will first find "loud" in the index to get a list of [0,7,5] (for example), and then find "cars" to get a list of [0,5,7,10]. Then, I will find where these lists intersect and return the ArrayList elements that correspond to these locations.
My current HashMap declartion looks like this: public HashMap<String, ArrayList<Integer>> map = new HashMap<>(); however even when the Key is different, the values stored in the ArrayList are the same because there is only one of them.
My Disks ArrayList is: public ArrayList<Disks> items; Would there be a way to incorporate this ArrayList into the Value of the HashMap?

Add a new value to the index entry for "Cars"
map.get("Cars").add(10);
Safe way to do this (key = "Cars", index = 10):
ArrayList<Integer> entry = map.get(key);
if (entry == null) {
entry = new ArrayList<Integer>();
map.put(key, entry);
}
entry.add(index);
Instead of using
HashMap<String, ArrayList<Integer>>
I'd recommend
HashMap<String, HashSet<Integer>>
Which is automatically avoids duplicates.
When you search for multiple words, use retainAll to build the intersection of multiple sets (but copy the first set because retainAll is destructive):
Set<Integer> resultSet = new HashSet<Integer>();
resultSet.addAll(map.get("Cars"));
resultSet.retainAll(map.get("Loud"));

You would need to create a new ArrayList of Integer for every string mapping to a value. The first time an entry is used, you create a new list (You must check that the string maps to null), and add the value of the index that the new Disk entry will be stored at in your ArrayList of Disls to you ArrayList of Integers. Any time the string maps to a non-empty list, then you just add the index (where it is in the Disk ArrayList) to the ArrayList of Integer.

Honestly, I think the best way for you to scale your solution is by using bloom filters or something sophisticated like this. This would require you to create complex hash codes, manage false positives, among other things.
Having that said, based on your design, I think what you can simply have a hash map pointing to the Disks objects that are also stored on the array list.
public HashMap<String, ArrayList<Disks>> map
For the keyword "cars", you have a list of Disks objects. For the keyword "loud" you have another list of Disks objects. Just take both lists and find the intersection, using the retainAll() method.
Make sure to override hashCode() and equals() in Disks so all collections will work fine.

How to perform a group by (sql) in Java

I have a text file which looks like this:
code appearance
----------------
j4t8 1
fj89 3
pf6n 1
j4t8 5
And I want to sort by the codes which appear the most. As you can see (and since I want to perform a group by) there are duplicate codes, so using HashMap would be a problem (duplicate keys). Any ideas?

don't know if this is the best solution but you could create a map of a list like this:
Map<String, List<Integer>> map = new HahsMap<String, List<Integer>>();
if(map.contains.(key))
{
map.get(key).add(new_appearance_value);
}
else
{
List<Integer> app = new ArrayList<Integer>();
app.add(new_appearance_value);
map.put(key, app);
}
Where the map key would be the code and the values of appearance would go into the list.
Note: to determine which code has more appearances just check for the size of the list of each code.

You can use
HashMap map = new HashMap<String, List<Integer>>();
The appearances will be stored in a list associated with every code.
Then given a code you just retrieve the list of integers and iterate over it.

You need a Collection of Pair objects. Each pair holds the code and the appearance. You then sort the collection using a Comparator, which only compares the appearance in each Pair object, and disregards the code.

The Commons Collections MultiValueMap can be used to decorate another map, allowing it to have more than one value for a key.

How to get all the entries from a LinkedHashMap in Java?

I am using String object as the key to a linkedhashmap.
How can I get all the entries in the LinkedHashMap?

You have three options that depend on whether you need just keys, just values or both
Set<String> keys = yourMap.keySet();
Collection<YourValueClass> values = yourMap.values();
Set<Map.Entry<String,YourValueClass>> pairs = yourMap.entrySet();
then you can easily iterate over them if you need. Actually all of them allow iterating using a simple foreach loop:
for (Map.Entry<String,YourClassValue> e : yourMap.entrySet())
// do something

You can use the entrySet method, which returns a set containing the key-value pairs in your map.