如何在Java中通过Map进行迭代? [英] How to iterate through a Map in java?

问题描述

我需要遍历BucketMap并获取所有keys，但是例如如何在不尝试手动操作的情况下到达buckets[i].next.next.next.key之类的东西，就像我在这里尝试的那样:

I need to iterate through a BucketMap and get all keys but how do I get to something like buckets[i].next.next.next.key for instance without doing it manually as I tried here:

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;
}

我还如何使用迭代完成后得到的j版本初始化String[] allkeys作为索引?

Also how can I initialize the String[] allkeys using the version of j we get after the iteration is done as the index?

推荐答案

对于基本的使用，HashMap是最好的，我已经介绍了如何对其进行迭代，比使用迭代器更容易:

For basic utilisation, the HashMap is the best, I've put how to iterate over it, easier than using an iterator :

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("Jack","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());
    }
}

快速说明:

for (String name : mp.keySet()){
        //Do Something
}

意思是:对于映射键中的所有字符串，我们都会做一些事情，并且在每次迭代时，我们都会将键称为名称"(它可以是您想要的任何东西，它是一个变量)

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)

我们在这里:

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;
}

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