Java HashMap键值的存储和检索
Java HashMap键值的存储和检索
提问于 2012-06-15 18:17:43
我想存储值并从Java HashMap中检索它们。
这就是我到目前为止所知道的：
public void processHashMap()
{
HashMap hm = new HashMap();
hm.put(1,"godric gryfindor");
hm.put(2,"helga hufflepuff");
hm.put(3,"rowena ravenclaw");
hm.put(4,"salazaar slytherin");
}我想以Java Collection或实用程序集(例如LinkedList)的形式从HashMap中检索所有键和值。
我知道如果我知道密钥，我可以得到值，如下所示：
hm.get(1);有没有办法以列表的形式检索键值？
回答 6
Stack Overflow用户
发布于 2012-06-15 18:29:37
我使用这三种方法来迭代映射。所有方法(keySet、values、entrySet)都返回一个集合。
// Given the following map
Map<KeyClass, ValueClass> myMap;
// Iterate all keys
for (KeyClass key : myMap.keySet())
System.out.println(key);
// Iterate all values
for (ValueClass value : myMap.values())
System.out.println(value);
// Iterate all key/value pairs
for (Entry<KeyClass, ValueClass> entry : myMap.entrySet())
System.out.println(entry.getKey() + " - " + entry.getValue());从Java8开始，我经常在lambda expressions中使用Streams。
// Iterate all keys
myMap.keySet().stream().forEach(key -> System.out.println(key));
// Iterate all values
myMap.values().parallelStream().forEach(value -> System.out.println(value));
// Iterate all key/value pairs
myMap.entrySet().stream().forEach(entry -> System.out.println(entry.getKey() + " - " + entry.getValue()));Stack Overflow用户
发布于 2012-06-15 18:19:54
map.keySet()会给你所有的钥匙
Stack Overflow用户
发布于 2014-02-22 06:27:19
//import statements
import java.util.HashMap;
import java.util.Iterator;
import java.util.TreeMap;
// hashmap test class
public class HashMapTest {
public static void main(String args[]) {
HashMap<Integer,String> hashMap = new HashMap<Integer,String>();
hashMap.put(91, "India");
hashMap.put(34, "Spain");
hashMap.put(63, "Philippines");
hashMap.put(41, "Switzerland");
// sorting elements
System.out.println("Unsorted HashMap: " + hashMap);
TreeMap<Integer,String> sortedHashMap = new TreeMap<Integer,String>(hashMap);
System.out.println("Sorted HashMap: " + sortedHashMap);
// hashmap empty check
boolean isHashMapEmpty = hashMap.isEmpty();
System.out.println("HashMap Empty: " + isHashMapEmpty);
// hashmap size
System.out.println("HashMap Size: " + hashMap.size());
// hashmap iteration and printing
Iterator<Integer> keyIterator = hashMap.keySet().iterator();
while(keyIterator.hasNext()) {
Integer key = keyIterator.next();
System.out.println("Code=" + key + " Country=" + hashMap.get(key));
}
// searching element by key and value
System.out.println("Does HashMap contains 91 as key: " + hashMap.containsKey(91));
System.out.println("Does HashMap contains India as value: " + hashMap.containsValue("India"));
// deleting element by key
Integer key = 91;
Object value = hashMap.remove(key);
System.out.println("Following item is removed from HashMap: " + value);
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/11048783
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