为什么一定要写 HashMap copy = new HashMap<>(map); 我没写这个自己测试也可以删除啊，但是提交通过不了。求帮助

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public static void removeFirstNameDuplicates(Map<String, String> map) {
        HashMap<String, String> copy = new HashMap<>(map);

        for (String name : copy.values()) {
            int count = 0;
            for (String _name : map.values()) {
                if (_name.equals(name)) count++;
            }
            if (count > 1) {
                removeItemFromMapByValue(map, name);
            }
        }
    }

另外，想请问一下， HashMap<String, String> copy = new HashMap<>(map); 这一句小括号内的（map）是什么意思啊，没有查到相关的用法

package zh.codegym.task.task08.task0817; import java.util.HashMap; import java.util.Map; /* 我们不需要重复的内容 */ public class Solution { public static HashMap<String, String> createMap() { HashMap<String, String> map = new HashMap<>(); map.put("Stallone", "Sylvester"); map.put("Stallone2", "Bruce"); map.put("Stallone3", "Arnold"); map.put("Schwarzenegger", "Sylvester"); map.put("Schwarzenegger2", "Bruce"); map.put("Schwarzenegger3", "Arnold"); map.put("Willis", "Sylvester"); map.put("Willis2", "Bruce"); map.put("Willis3", "Arnold"); map.put("Stallone4", "Sylvester4"); return map; } public static void removeFirstNameDuplicates(Map<String, String> map) { for (String name : map.values()) { int count =0; for (String _name : map.values()) { if(name.equals(_name)){ count++; } } if(count>1){ removeItemFromMapByValue(map,name); } } } public static void removeItemFromMapByValue(Map<String, String> map, String value) { HashMap<String, String> copy = new HashMap<String, String>(map); for (Map.Entry<String, String> pair : copy.entrySet()) { if (pair.getValue().equals(value)) map.remove(pair.getKey()); } } public static void main(String[] args) { } }

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Guadalupe Gagnon

级别 37 ，Tampa，United States

23 三月 2021, 14:00

The best thing to do is test that the code does exactly as intended. In this task you have 2 sub tasks to complete: #1 Create a HashMap<String, String> that contains 10 items #2 Take a HashMap<String, String> and remove from it all entries where the value is the same value as any of the other entries with the addition that you have to use the removeFirstNameDuplicates() method to do the actual removal of items. I don't know how you tested it prior, but I would recommend testing each method:

public static void main(String[] args) {
   // step1: use the createMap() method to create a  HashMap<String, String>
   HashMap<String, String> test = createMap();
   // step2: output the result. Count the elements to ensure that there are 10
   System.out.println(test);

   // step3: pass the created map to the removeFirstNameDuplicates() for testing
   removeFirstNameDuplicates(test);
   // step4: output the result to ensure all required elements are removed
   System.out.println(test);
}

I can tell you right now that step 3 above will fail because it is an illegal operation to remove items from a collection that you are iterating over without using the Iterator.remove() method. This will result in a .ConcurrentModificationException being thrown and the program crashing. You have mentioned one solution to this problem: by creating a copy first to iterate over you can safely remove items from the original collection without breaking the rule. This is one acceptable method to solve this task, but not the only one. When you finally get this code working ensure to test the removeFirstNameDuplicates() to ensure that it works correctly with any Map<String, String> that you pass to it, not just the one from your createMap() method. The task does not say that it has to only work that way and it will be tested by the validator with multiple maps of varying lengths and entries.