How do you use a hashmap?

2 years ago
Liam
1 minute

HashMap is a data structure in Java that is used to store mapping relationships between keys and values. Here are some common operations when using HashMap:

  1. Create a HashMap object:
HashMap<String, Integer> hashMap = new HashMap<>();
  1. Add key-value pair:
hashMap.put("key1", 1);
hashMap.put("key2", 2);
  1. Get value:
int value = hashMap.get("key1"); // 获取键"key1"对应的值
  1. Check if the key exists:
boolean containsKey = hashMap.containsKey("key1"); // 判断是否包含键"key1"
  1. Check if the value exists.
boolean containsValue = hashMap.containsValue(1); // 判断是否包含值1
  1. Remove key-value pair.
hashMap.remove("key2"); // 移除键"key2"对应的键值对
  1. Iterate through key-value pairs:
for (Map.Entry<String, Integer> entry : hashMap.entrySet()) {
    String key = entry.getKey();
    int value = entry.getValue();
    System.out.println(key + ": " + value);
}

Note: The keys in a HashMap are unique, if a key that is already existing is added, the new value will replace the old value.

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