How to use collections correctly in Java?

Properly using collections in Java involves many aspects, including choosing the appropriate collection type, understanding its performance characteristics, and following best practices. Here are some guidelines on how to use Java collections correctly:

1. Choose the right collection type

Learn about the properties of different collections :
- List(e.g. ArrayListand LinkedList): An ordered collection that can contain repeated elements. Suitable for accessing elements through indexes.
- Set(e.g. HashSetand TreeSet): A collection that does not contain duplicate elements. HashSetUsually faster, but ordering is not guaranteed; TreeSetsort by natural order or a custom comparator.
- Map(such as HashMapand TreeMap): stores key-value pairs. HashMapIt is a general-purpose Map, TreeMapsorted by key.
Choose a collection based on your needs :
- Consider using if you need to find elements frequently HashSet.
- If you need to keep the order of elements, use ArrayListor LinkedHashSet.
- If key-value mapping is required and the keys are unique, use Mapthe implementation.

2. Use generics

Use generics to ensure type safety of elements in a collection and avoid runtime errors.
```
List<String> list = new ArrayList<>();
```

3. Optimize performance

Consider the capacity of the collection when initializing, especially for ArrayListand HashMap. This reduces the number of reallocations and copies of data.
```
List<String> list = new ArrayList<>(initialCapacity);
```

4. Use interfaces as type references

Use interface types (such as List, Set, Map) to reference collections whenever possible, which improves the flexibility of the code.
```
List<String> list = new ArrayList<>();
```

5. Traverse the collection

Use a for-each loop or iterator to iterate over the collection.

for (String element : list) {
      
      
    // 处理 element
}

6. Avoid concurrent modification exceptions

When traversing a collection, do not directly modify the collection (add, delete elements). If you need to modify, you can use the iterator's removemethod, or collect the items you want to change during the traversal, and then modify them after the traversal ends.

7. Use collection tool classes

Use Collectionsthe methods provided by the class, such as sorting, reversing, thread-safe wrapping, etc.
```
Collections.sort(list);
```

8. Consider thread safety

If using collections in a multi-threaded environment, consider thread-safe collections such as ConcurrentHashMap, or Collections.synchronizedListwrap ordinary collections using methods such as .
```
List<String> syncList = Collections.synchronizedList(new ArrayList<>());
```

Following these principles can help you use Java collections more effectively and avoid common pitfalls. Remember, which collection type you choose depends on your specific needs and application scenario.