Java - Map -＞ key - case sensitive

public static void main(String[] args) {  
    Map<String, String> map = new HashMap<>();  
  
    map.put("strain", "s1");  
    map.put("sTrain", "s2");  
  
    System.out.println(map);  
  
    map.put("strain", "s3");  
    System.out.println(map);  
}      

{strain=s1, sTrain=s2}  
{strain=s3, sTrain=s2}