JavaAdding List to TreeMap and Display out key and list

Try this code. Its working. By the way you should improve this code. The code is not optimised.

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import java.util.TreeMap;

public class Treemap {

private List<String> fList = new ArrayList<String>();
private TreeMap<Integer, List<String>> tMap = new TreeMap<Integer, List<String>>();

public static void main(String[] args) {
    Treemap tm = new Treemap();
    String file = "";
    if (args.length == 1) {
        file = args[0];

        try {
            tm.Read(file);
        } catch (IOException ex) {
            System.out.println("Error");
        }

    } else {
        System.out.println("Usage: java treemap 'Filename'");
        System.exit(1);
    }
}
public void Read(String file) throws IOException {
    //Scanner in = null;
    BufferedReader in = null;
    InputStream fis;

    try {
        fis = new FileInputStream(file);
        in = new BufferedReader(new InputStreamReader(fis));
        String line = null;
        while ((line = in.readLine()) != null) {

            String[] file_Array = line.split(" ", 2);

            if (file_Array[0].equalsIgnoreCase("1")) {
                Add(Integer.parseInt(file_Array[0]), file_Array[1]);
               // Display(1);
            } else if (file_Array[0].equalsIgnoreCase("3")) {
                Add(Integer.parseInt(file_Array[0]), file_Array[1]);
               // Display(3);
            } else if (file_Array[0].equalsIgnoreCase("4")) {
                Add(Integer.parseInt(file_Array[0]), file_Array[1]);
               // Display(4);
            }
        }
    } catch (IOException ex) {
        System.out.println("Input file " + file + " not found");
        System.exit(1);
    } finally {
        for(int i: tMap.keySet())
            Display(i);
        in.close();

    }
}
public void Add(int item, String fruit) {
    if (tMap.containsKey(item) == false) {
        fList = new ArrayList<>();
        fList.add(fruit);
        tMap.put(item, fList);

       // System.out.println("Fruits added " + item);
    } else {
        tMap.get(item).add(fruit);
       // System.out.println("not exist");
    }
}
public void Display(int item) {

    if (tMap.containsKey(item)) {
        System.out.print("Number " + item + ":" + "\n");
         System.out.print(tMap.get(item));
        System.out.print("\n");
    } else {
        System.out.print(item + " WAS NOT FOUND"+ "\n");
    }

}

}

You make unnecessary complicated your code. Try with simple code.

public class Treemap {

    public static void main(String[] args) throws FileNotFoundException {
        Scanner sc = new Scanner(new File("file.txt"));
        Map<Integer, List<String>> tMap = new TreeMap<>();

        while (sc.hasNextLine()) {
            String line = sc.nextLine();
            String[] values=line.split(" ");
            List<String> fList;
            Integer key=Integer.valueOf(values[0]);
            if(tMap.containsKey(key)){//Key already inserted
                fList=tMap.get(key); //Get existing List of key
                fList.add(values[1]);
            }
            else{
                fList = new ArrayList<String>();
                fList.add(values[1]);
                tMap.put(key, fList);
            }
        }
        for (Map.Entry<Integer, List<String>> entry : tMap.entrySet()) {
            System.out.println(entry.getKey());
            System.out.println(entry.getValue());
        }

    }
}

Output:

1
[apple, orange]
3
[pear, pineapple]
4
[dragonfruit]

Change some code for the method Add(), which is incorrect in your code.

What if the Map contains the key?

Following code is modified based on your code, hope this can help you some.

public void Add(int item, String fruit) {
    if (tMap.containsKey(item)==false) {
        fList.clear();
        fList.add(fruit);
        tMap.put(item, fList);

        System.out.println("Fruits added " + item);
    } else {
        tMap.get(item).add(fruit);
    }
}