如何将String对象存入ArrayList并改造ArrayList<HashMap<String,String>>元素结构？

Hey there! Let's tackle your two Java collection questions one by one.

First off, let's clarify what you're aiming for here—you either want to replace the HashMap elements in your original list with Strings, or create a new ArrayList for Strings while clearing out the original HashMap list. Let's cover both scenarios:

Scenario 1: Create a new String list and clear the original HashMap list #

This is the cleaner approach since mixing HashMap and String types in the same list isn't ideal (it breaks type safety). Here's how to do it:

// Your original HashMap list
ArrayList<HashMap<String, String>> statusList = new ArrayList<>();
// Assume this list is already populated with your HashMap entries

// New list to hold your Strings
ArrayList<String> stringList = new ArrayList<>();

// Extract the String value you need from each HashMap (e.g., status_name)
for (HashMap<String, String> map : statusList) {
    // Customize this to get the String you want—here we're using the status_name value
    String targetString = "status_name=" + map.get("status_name");
    stringList.add(targetString);
}

// Remove all HashMap elements from the original list
statusList.clear();

Scenario 2: Replace elements in the original list (not recommended for type safety) #

If you really need to modify the original list directly, note that you'll lose generic type safety (the list will become ArrayList<Object>). Example:

ArrayList<HashMap<String, String>> originalList = new ArrayList<>();
// Populate the list first

for (int i = 0; i < originalList.size(); ) {
    // Remove the HashMap at index i
    HashMap<String, String> map = originalList.remove(i);
    // Get your target String
    String value = map.get("status_name");
    // Add the String back at the same index
    originalList.add(i, value);
    i++;
}

Your input list is [{status_id=1, status_name=iceCream}, {status_id=2, status_name=cake (chocolate)}], and you want an output like [status_name=iceCream, status_name=cake(chocolate)]. It looks like you want a list of Strings in that key-value format—here's how to make it happen:

// Initialize your input list
ArrayList<HashMap<String, String>> statusList = new ArrayList<>();

HashMap<String, String> firstMap = new HashMap<>();
firstMap.put("status_id", "1");
firstMap.put("status_name", "iceCream");

HashMap<String, String> secondMap = new HashMap<>();
secondMap.put("status_id", "2");
secondMap.put("status_name", "cake (chocolate)");

statusList.add(firstMap);
statusList.add(secondMap);

// Create the result list
ArrayList<String> resultList = new ArrayList<>();

for (HashMap<String, String> map : statusList) {
    // Remove the status_id entry from the original map (if you need to modify it)
    map.remove("status_id");
    
    // Build the string in your desired format—remove spaces if needed
    String statusEntry = "status_name=" + map.get("status_name").replace(" ", "");
    resultList.add(statusEntry);
}

// Print the result—this will match your expected output
System.out.println(resultList);
// Output: [status_name=iceCream, status_name=cake(chocolate)]

If instead you wanted a list of HashMaps that only contain the status_name key (instead of Strings), you can adjust the code like this:

ArrayList<HashMap<String, String>> resultList = new ArrayList<>();

for (HashMap<String, String> map : statusList) {
    HashMap<String, String> trimmedMap = new HashMap<>();
    trimmedMap.put("status_name", map.get("status_name").replace(" ", ""));
    resultList.add(trimmedMap);
}

// Output will be: [{status_name=iceCream}, {status_name=cake(chocolate)}]

内容的提问来源于stack exchange，提问作者Ashley