java将HashMap元素放入foreach循环内仅使用最后一个

Question

I have a strength problem about adding elements into an HashMap inside a loop. I make sure to declare map before iteration, to ignore it's recreation each time but I got the same problem - in map remains only the last element from my loop iteration. The code is

//declare map         
Map<String, String> map = new HashMap<String, String>();

//my loop iteration
String[] array = {"element1", "element2", "element3"};
for (String str: array) {
map.put("uniqueKey", str);
}

as a result, for simplicity calling map.toString() , I get only {uniqueKey=element3}

I just don't understand why this happens, any explanations will be appreciated.

Answer 1

Well you're trying to ignore the general concept of Map s about unique keys. Make your "uniqueKey" "really" unique as you repeat it in the loop :)

I'll give you an example to understand:

 Map<String, String> map = new HashMap<>();
 map.put("1", str1);
 map.put("2", str2);
 map.put("3", str3);
 map.put("1", str4); // value str1 is overwritten by str4

Think of Map s as List s, but with indices other than primitive int s and without the need to have the indices in range 0 .. size-1