Java 使用 HashMap 遍历 ArrayList

Java iterate over ArrayList with HashMap in it

提问by Bham

I have a Hashmap with four answers. And I have for ex 2 questions. This is how i do it

我有一个带有四个答案的 Hashmap。我有前 2 个问题。这就是我的做法

    // Awnsers question 1
    antwoorden1.put("Hypertext Preprocessor", true);
    antwoorden1.put("Hypertext PHPprocessor", false);        
    antwoorden1.put("Hypertext processor", false);
    antwoorden1.put("Preprocessor PHP", false);
    // Awnsers question 2
    antwoorden2.put("Model view config", false);
    antwoorden2.put("Model view connect", false);        
    antwoorden2.put("Model view controllers", false);
    antwoorden2.put("Model view controller", true);  

Now I need to get access to all this information, so what I do is add the two HashMaps to one ArrayList

现在我需要访问所有这些信息，所以我要做的是将两个 HashMap 添加到一个 ArrayList

    // Add the Hashmaps to the arrayList
    alleAntwoorden.add(antwoorden1);
    alleAntwoorden.add(antwoorden2);

But how can I loop through the ArrayList to get the key and value from the HashMap? This is what I already tried.

但是如何遍历 ArrayList 以从 HashMap 中获取键和值？这是我已经尝试过的。

    for(int i = 0; i < alleAntwoorden.size(); i++)
    {
        for (Map.Entry<String, Boolean> entry : alleAntwoorden.get(i).entrySet())
        {
            String key = entry.getKey();
            Object value = entry.getValue();
            // ...
        }  
    }

But I always get the following msg: incompatible types

但我总是收到以下消息：不兼容的类型

Antwoorden1, antwoorden2 and alleAntwoorden are defined as:

Antwoorden1、antwoorden2 和 alleAntwoorden 定义为：

private ArrayList<HashMap> alleAntwoorden; 
private HashMap<String, Boolean> antwoorden1, antwoorden2;

采纳答案by ThisClark

On the following interfaces:

在以下接口上：

Map<String, Boolean> map1 = new HashMap<>();
Map<String, Boolean> map2 = new HashMap<>();
List<Map<String, Boolean>> list = new ArrayList<>();

We may iterate with foreach loops:

我们可以使用 foreach 循环进行迭代：

for (Map<String, Boolean> entry : list) {
    for (String key : entry.keySet()) {
        Boolean value = entry.get(key);
        System.out.println("key = " + key);
        System.out.println("value = " + value);
    }
}

回答by Marcin Szymczak

If you are using Eclipse you can just write entry.getValue(). Put cursor on top of it and use keyboard shortcut Ctrl+2, l, which automatically resolves correct type.

如果您使用的是 Eclipse，则只需编写entry.getValue(). 将光标放在它上面并使用键盘快捷键 Ctrl+2, l，它会自动解析正确的类型。

For IntelliJ it works almost the same, but with Ctrl+Alt+v

对于 IntelliJ，它的工作原理几乎相同，但使用 Ctrl+Alt+v

回答by Tom

From the comment:

从评论：

private ArrayList<HashMap> alleAntwoorden;

This is the problem. You're using a raw type map, but you're trying to assign a single entry to the variable Map.Entry<String, Boolean>. This cannot work, because your current map is of type HashMap<Object, Object>. Change the variable alleAntwoordento:

这就是问题。您正在使用原始类型映射，但您试图将单个条目分配给变量Map.Entry<String, Boolean>。这行不通，因为您当前的地图类型为HashMap<Object, Object>。将变量更改alleAntwoorden为：

private List<Map<String, Boolean>> alleAntwoorden;

Mind, that I've also changed the types to their Interface type: Should you always Code To Interfaces In Java.

请注意，我还将这些类型更改为它们的接口类型：您是否应该始终在 Java 中编写接口代码。

回答by razcor

As stated by other users, there are better ways to do this kind of task, but if you want to use your approach, this a functioning code snippet:

正如其他用户所说，有更好的方法来完成这种任务，但如果你想使用你的方法，这是一个功能性的代码片段：

    HashMap antwoorden1 = new HashMap();
    HashMap antwoorden2 = new HashMap();

       // Awnsers question 1
    antwoorden1.put("Hypertext Preprocessor", true);
    antwoorden1.put("Hypertext PHPprocessor", false);        
    antwoorden1.put("Hypertext processor", false);
    antwoorden1.put("Preprocessor PHP", false);
    // Awnsers question 2
    antwoorden2.put("Model view config", false);
    antwoorden2.put("Model view connect", false);        
    antwoorden2.put("Model view controllers", false);
    antwoorden2.put("Model view controller", true);  

    ArrayList<HashMap> alleAntwoorden =  new ArrayList<HashMap>();

    // Add the Hashmaps to the arrayList
    alleAntwoorden.add(antwoorden1);
    alleAntwoorden.add(antwoorden2);

    for(int i = 0; i < alleAntwoorden.size(); i++)
    {

         Iterator it = (Iterator)alleAntwoorden.get(i).entrySet().iterator();

         while (it.hasNext()) {
            Map.Entry pairs = (Map.Entry)it.next();
            System.out.println(pairs.getKey() + " = " + pairs.getValue());
            it.remove(); // avoids a ConcurrentModificationException
        }

    }

回答by David Soroko

Everything should work with the following definitions:

一切都应符合以下定义：

Map<String, Boolean> antwoorden1 = new HashMap<>();
Map<String, Boolean> antwoorden2 = new HashMap<>();
List <Map<String, Boolean>> alleAntwoorden = new ArrayList<>();