如何遍历java中的Map？
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How to iterate through a Map in java?
提问by NoIdea
I need to iterate through a BucketMapand get all keysbut how do I get to something like buckets[i].next.next.next.keyfor instance without doing it manually as I tried here:
我需要遍历 aBucketMap并获取所有内容，keys但如何在buckets[i].next.next.next.key不手动执行的情况下获得类似的内容，就像我在这里尝试的那样：
public String[] getAllKeys() {
int j = 0; //index of string array "allkeys"
String allkeys[] = new String[8];
for(int i = 0; i < buckets.length; i++) { //iterates through the bucketmap
if(buckets[i] != null) { //checks wether bucket has a key and value
allkeys[j] = buckets[i].key; //adds key to allkeys
j++; // counts up the allkeys index after adding key
if(buckets[i].next != null) { //checks wether next has a key and value
allkeys[j] = buckets[i].next.key; //adds key to allkeys
j++;
}
}
}
return allkeys;
}
Also how can I initialize the String[] allkeysusing the version of jwe get after the iteration is done as the index?
另外，如何String[] allkeys使用j迭代完成后获得的版本作为索引来初始化？
采纳答案by azro
For basic utilisation, the HashMap is the best, I've put how to iterate over it, easier than using an iterator :
对于基本使用，HashMap 是最好的，我已经介绍了如何迭代它，比使用迭代器更容易：
public static void main (String[] args) {
//a map with key type : String, value type : String
Map<String,String> mp = new HashMap<String,String>();
mp.put("John","Math"); mp.put("Hyman","Math"); map.put("Jeff","History");
//3 differents ways to iterate over the map
for (String key : mp.keySet()){
//iterate over keys
System.out.println(key+" "+mp.get(key));
}
for (String value : mp.values()){
//iterate over values
System.out.println(value);
}
for (Entry<String,String> pair : mp.entrySet()){
//iterate over the pairs
System.out.println(pair.getKey()+" "+pair.getValue());
}
}
A quick explanation :
快速解释：
for (String name : mp.keySet()){
//Do Something
}
means : "For all string from the keys of the map, we'll do something, and at each iteration we will call the key 'name' (it can be whatever you want, it's a variable)
意思是：“对于来自地图键的所有字符串，我们会做一些事情，并且在每次迭代时我们将调用键'name'（它可以是任何你想要的，它是一个变量）
Here we go :
开始了 ：
public String[] getAllKeys(){
int i = 0;
String allkeys[] = new String[buckets.length];
KeyValue val = buckets[i];
//Look at the first one
if(val != null) {
allkeys[i] = val.key;
i++;
}
//Iterate until there is no next
while(val.next != null){
allkeys[i] = val.next.key;
val = val.next;
i++;
}
return allkeys;
}
回答by DNAj
See if this helps,
看看这是否有帮助，
HashMap< String, String> map = new HashMap<>();
Set<String> keySet = map.keySet();
Iterator<String> iterator = keySet.iterator();
while(iterator.hasNext())
{
//iterate over keys
}
//or iterate over entryset
Iterator<Entry<String, String>> iterator2 = map.entrySet().iterator();
while(iterator2.hasNext())
{
Entry<String, String> next = iterator2.next();
//get key
next.getKey();
//get value
next.getValue();
}
回答by Johnny
With Java 8, I would suggest you to use Stream API.
对于 Java 8，我建议您使用 Stream API。
It will allow you to iterate through the Map in a much more convenient approach:
它将允许您以更方便的方法遍历 Map：
public void iterateUsingStreamAPI(Map<String, Integer> map) {
map.entrySet().stream()
// ...
.forEach(e -> System.out.println(e.getKey() + ":" + e.getValue()));
}
Check out for more examples about iteration through maps in Java.
查看有关Java 中映射迭代的更多示例。
