How to use different types of keys in one map in Java?
Apr 19, 2025 pm 05:45 PM
How to use different types of keys in Java?
In Java programs, Map is a common data structure that stores key-value pairs. But sometimes different types of keys are needed in a Map, such as integers and strings. Using different types as keys directly will throw a type mismatch error. This article will explore how to store different types of keys in Java Map and solve related problems.
Let’s first look at an example and try to add different types of key-value pairs to a custom dictionary class MyDictionary :
public class MyDictionary<k v> implements DictionaryInterface<k v> {
private map<k v> map;
public MyDictionary() {
map = new HashMap();
}
public void add(K key, V value) {
map.put(key, value);
}
public V get(K key) {
return map.get(key);
}
}
public class Main {
public static void main(String[] args) {
MyDictionary<integer string> dictionary = new MyDictionary();
dictionary.add(1, "100");
dictionary.add("1", "full score"); // Compile error}
}</integer></k></k></k>
In the above code, the type parameter of MyDictionary is defined as<k v></k> , supports any type of keys and values. But when trying to add a string type key to MyDictionary<integer string></integer> When , the compiler will report an error because the key type does not match the definition.
The solution is to define the type of key and value as Object :
public static void main(String[] args) {
MyDictionary<object object> dictionary = new MyDictionary();
dictionary.add(1, 100);
dictionary.add("1", "full score"); // Compile passed}</object>
By modifying the type parameter of MyDictionary to<object object></object> , you can freely add different types of keys. But this method requires type conversion when used, because Object type may cause a runtime type error.
In short, using Object as the type of key and value can store different types of keys in Java Map, but type conversions need to be handled with caution to avoid runtime errors. A better approach is to choose the right key type according to actual needs, or consider using more advanced data structures, such as custom classes as keys to encapsulate different types of data.
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