Java 如何将 HashMap 添加到 ArrayList
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How to add HashMap to ArrayList
提问by AhabLives
Can someone please tell me why the code below overwrites every element in the ArrayList with the most recent entry into the ArrayList? Or how to correctly add new elements of hashmaps to my ArrayList?
有人能告诉我为什么下面的代码会用最近进入 ArrayList 的条目覆盖 ArrayList 中的每个元素吗？或者如何将哈希图的新元素正确添加到我的 ArrayList 中？
ArrayList<HashMap<String, String>> prodArrayList = new ArrayList<HashMap<String, String>>();
HashMap<String, String> prodHashMap = new HashMap<String, String>();
public void addProd(View ap)
{
// test arraylist of hashmaps
prodHashMap.put("prod", tvProd.getText().toString());
prodArrayList.add(prodHashMap);
tvProd.setText("");
// check data ///
Log.e("myLog","Data prodArrayList in ADD Method Size = "+prodArrayList.size());
for(int i=0; i< prodArrayList.size();i++)
{
Log.e("myLog","Data prodArrayList in ADD Method = "+prodArrayList.get(i).toString());
}
}
采纳答案by Rod_Algonquin
problem:
问题：
prodHashMap.put("prod", tvProd.getText().toString());
You are using the same key each time you are adding an element to the the arraylist with the same reference to the HashMapthus changing its values.
每次将元素添加到 arraylist 时，您都使用相同的键，并HashMap对其值具有相同的引用。
Solution:
解决方案：
create a new instance of HashMapeach time you want to add it to the ArrayListto avoid changing its values upon calling addProd
HashMap每次要将其添加到 时创建一个新实例，ArrayList以避免在调用时更改其值addProd
public void addProd(View ap)
{
// test arraylist of hashmaps
HashMap<String, String> prodHashMap = new HashMap<String, String>();
prodHashMap.put("prod", tvProd.getText().toString());
prodArrayList.add(prodHashMap);
tvProd.setText("");
// check data ///
Log.e("myLog","Data prodArrayList in ADD Method Size = "+prodArrayList.size());
for(int i=0; i< prodArrayList.size();i++)
{
Log.e("myLog","Data prodArrayList in ADD Method = "+prodArrayList.get(i).toString());
}
}
回答by umamaheshwar g
This is for adding multiple maps to List
这是用于将多个地图添加到列表
Map<String,Object> map1=new HashMap<>();
map1. // add required items
Map<String,Object> map2=new HashMap<>();
map2. // add required items
Map<String,Object> map3=new HashMap<>();
map3. // add required items
List<String,Object> list=new ArrayList<>();
list.add(map1);
list.add(map2);
list.add(map3);
