How to allow duplicate keys in map in java?

        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        Map<String,Double> map=new LinkedHashMap<String,Double>();
        line=br.readLine();        
        while(!line.equals("End")) {
        	String[]arr2=line.split(" ");
        	String model=arr2[1];
        	Double distance=Double.parseDouble(arr2[2]);
        	map.put(model, distance);
        	line=br.readLine();
        }

<br>Im trying to print all the keys and values although they are duplicate.
<br>My input should be
<br>Audi 15.3
<br>Audi 8.6
<br>BMW 45
<br>End
<br><br> And when im trying to print it, it gives me only (Audi 8.6 and Bmw 45).
<br>I need to print twice audi!

You can't have duplicate keys in a map. The best you can do is have something like a list in the values. i.e. Map<String, List<Double>> map = new HashMap<String, List<Double>>();

The best approach is using object-oriented programming.

Create new class

class Result {
    String model;
    String distance;

    public Result(String model, String distance) {
        this.model = model;
        this.distance = distance;
    }
}

Change type of

from

Map<String,Double> map = new LinkedHashMap<String,Double>();

to:

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

Change adding method

from:

map.put(model, distance);

to:

list.add(Result(model, distance));

You Map declaration looks like Map<String, Double> that means, that only one Double value can be mapped to String key.

You can simply, change Double to List<Double> and map a key to the list, then your case look like:

BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
Map<String, List<Double>> map=new LinkedHashMap<>();
line=br.readLine(); 
while(!line.equals("End")) {
    String[] arr2=line.split(" ");
    String model=arr2[1];
    Double distance=Double.parseDouble(arr2[2]);
    List<Double> distances = map.computeIfAbsent(model, key -> new ArrayList<>());
    distances.add(distance);
    line=br.readLine();
}

This structure more correct, meaning the model Audi has a list of different distances. Key one Audi and list of values.

You can't have duplicate keys in a straight-forward Java map. One approach you can use it to hold a List of values instead of a single value, and iterate over them when you're printing out the results:

BufferedReader be = new BufferedReader(new InputStreamReader(System.in));
Map<String, List<Double>> map = new LinkedHashMap<>();
line=br.readLine();        
while(!line.equals("End")) {
    String[] arr2 = line.split(" ");
    String model = arr2[1];
    Double distance = Double.parseDouble(arr2[2]);
    map.computeIfAbsent(model, m -> new LinkedList<>()).add(distance);
    line = br.readLine();
}

And then, when you print it out:

for (Map.Entry<String, List<Double>> entry : map) {
    for (Double d : entry.getValue()) {
        System.out.println(entry.getKey() + " " d);
    }
}

It's not my favourite thing to do, but there is a workaround to allow duplicates in a Map. The LinkedHashMap you are using, uses the hashCode method defined in Object.
You could create a wrapper class around String, without overriding the default implementation of equals and hashCode. This would allow you to add "duplicates" to your collection, because Java thinks they are not identical.

Example class:

public class StringWrapper {
   private String value;

   public StringWrapper(String value) {
      this.value = value;
   }

// getters and setters
// no equals and hashcode
}