How does Treemap works?

Question

So I'm trying to read data from an excel file and I use Treemap to read the file. But the problem is that treemap puts my data random into its list. Although, I set an index when I use it.

//This writes the data from an old file
//writer is my treemap
//sReadData is a List with the old data

for (int i = 0; i < (sReadData.size()+1)/5; i++) {
                
     writer.put(String.valueOf(i),new Object[] { sReadData.get(i*5),sReadData.get(i*5+1),sReadData.get(i*5+2),sReadData.get(i*5+3),sReadData.get(i*5+4)});
}
            

writer.put(String.valueOf(iCounter +1), new Object[] { "Name", "Date","Time", "Type","Owner"});

//This writes the new data
for (int i = 0; i < sName.length; i++) {
                              //iCounter is just the number of rows from the old file|These are just some Array with some data
     writer.put(String.valueOf(iCounter+2+i), new Object[] { sName[i], sDate[i],sTime[i], sTypes[i],sOwners[i]});
}

My mistake was that I initialized my treemap wrong. It should be like this: Map<Integer, Object[]> tMap = new TreeMap<Integer, Object[]>();

Answer 1

The order won't be random. But it may not be what you expect. Strings are ordered lexically, so that "1" < "10" < "100" < ... < "11" ... < "2".

If you want the TreeMap entries to be returned in numerical order, use Integer as the key type.

---

When I try to use an int instead of a String, I get this error:

 The method put(String, Object[]) in the type Map<String,Object[]>
 is not applicable for the arguments (int, Object[])

You also need to change the declaration of the map to TreeMap<Integer, Object[]>.