How to convert all values ​​in Java Map to String type

You can use the Map.replaceAll() method in Java 8 to convert all values ​​​​to the String type:

Map<String, Object> map = new HashMap<>();
// 添加一些键值对
map.put("key1", 123);
map.put("key2", true);
map.put("key3", new Date());
// 将所有的值转为 String 类型
map.replaceAll((k, v) -> String.valueOf(v));

The above code will map All values ​​are converted to String type.

HashMap is one of the most widely used collection classes in Java. It is a very fast key-value pair storage method that can be used to store and access large amounts of data. Here are some common methods of HashMap:

• put(key, value): Add a key-value pair to HashMap.

HashMap<String, Integer> map = new HashMap<>();
   map.put("apple", 1);
   map.put("banana", 2);

• get(key): Get the corresponding value based on the key.

Integer value = map.get("apple");

• containsKey(key): Determine whether the HashMap contains the specified key.

if (map.containsKey("apple")) {
       // ...
   }

• containsValue(value): Determine whether the HashMap contains the specified value.

if (map.containsValue(1)) {
       // ...
   }

• remove(key): Delete a key-value pair in the HashMap based on the key.

map.remove("apple");

• keySet(): Returns the set of all keys in the HashMap.

Set<String> keys = map.keySet();

• values(): Returns the collection of all values ​​in the HashMap.

Collection<Integer> values = map.values();

• entrySet(): Returns the set of all key-value pairs in the HashMap.

Set<Map.Entry<String, Integer>> entries = map.entrySet();

The above are the commonly used HashMap methods. There are other methods. You can check the relevant documents for more information.

HashMap mainly uses Hash algorithm and array for storage. In HashMap, each key-value pair corresponds to an element in an array, which is called a "bucket" or "slot".

The index value of the array is calculated through the Hash algorithm. Each bucket stores a linked list that stores key-value pairs. If the index values ​​calculated by different key-value pairs are the same, these key-value pairs will be placed in the same bucket and stored in the bucket in the form of a linked list. This is HashMap's conflict resolution method.

The stored procedure of HashMap is as follows:

• When using the put method to add a key-value pair to a HashMap, the key will first be hashCode value calculates the array index position. The specific method is to perform some operations on the hashCode value to obtain an array index value. This index value is the position of the key-value pair in the array.

• If the position in the array is empty, you can directly store the key-value pair in this position to complete the addition operation.

• If there is already a key-value pair at the location, then you need to compare the equals method of the key to determine whether to update the value of the key-value pair or Add a new key-value pair.

• When the length of the linked list is long, the performance of HashMap may be affected because the entire linked list may need to be traversed when searching.

To this end, Java 8 introduced the "Red-Black Tree" data structure, which can convert a linked list into a tree to improve performance. If used in a multi-threaded environment, it should be noted that the non-thread safety of HashMap may lead to exceptions. If you need to use HashMap in a multi-threaded environment, you can use the ConcurrentHashMap or Collections.synchronizedMap method to achieve thread safety.

The above is the detailed content of How to convert all values ​​in Java Map to String type. For more information, please follow other related articles on the PHP Chinese website!