1. ArrayList annotation translation
Resizable-array implementation of the List interface. Implements all optional list operations, and permits all elements, including null. In addition to implementing the List interface, this class provides methods to manipulate the size of the array that is used internally to store the list. (This class Is roughly equivalent to Vector, except that it is unsynchronized.) ArrayList is a mutable array implementation of the List interface. ArrayList implements all optional list operations and allows all elements, including NULL. In addition to implementing the List interface, ArrayList provides methods to manipulate the size of arrays that are used internally to store lists. (ArrayList is roughly the same as Vector, except that ArrayList is thread-safe.)
The size, isEmpty, get, set, iterator, and listIterator operations run in constant time. The add operation runs in amortized constant time, that is, adding n elements requires O(n) time. All of the other operations run in linear time (roughly speaking). The constant factor is low compared to that for the LinkedList implementation. The size, isEmpty, get, set, iterator, and listIterator operations require constant time. The add operation requires constant amortized time, that is, the time required to add n elements is O(n). All other operations take linear time (roughly speaking). This constant factor is low compared to LinkedList.
Each ArrayList instance has a capacity. The capacity is the size of the array used to store the elements in the list. It is always at least as large as the list size. As elements are added to an ArrayList, its capacity grows automatically. The details of the growth policy are not specified beyond the fact that adding an element has constant amortized time cost. Each ArrayList instance has one capacity. This capacity is the size of the array used to store the elements of the list. This capacity is at least as large as the size of the list. The ArrayList automatically expands when elements are added to it. The details of the growth policy are not specified except for the constant time after adding an element to spend amortized.
An application can increase the capacity of an ArrayList instance before adding a large number of elements using the ensureCapacity operation. This may reduce the amount of incremental reallocation. An application can use the ensureCapacity operation to increase the capacity of an ArrayList instance before adding a large number of elements. This reduces the number of incremental reallocations.
Note that this implementation is not synchronized. If multiple threads access an ArrayList instance concurrently, and at least one of the threads modifies the list structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more elements, or explicitly resizes the backing array; merely setting the value of an element is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the list. If no such object exists, the list should be “wrapped” using the Collections.synchronizedList method. This is best done at creation time, To prevent accidental unsynchronized access to the list: Note: This implementation is thread-safe. If multiple threads access an ArrayList instance at the same time, and at least one thread modifies the list structurally, it must be synchronized externally. (Structural changes are any additions or deletions of one or more elements, resizing internal arrays; Simply setting the value of an element is not a structural change. This is usually done by synchronizing an object to naturally encapsulate the list. If there are no such objects exist, this list should be in the Collections. SynchronizedList approach to packaging. In order to prevent accidental asynchronous access this list, this is best done at creation time: list the list = Collections. SynchronizedList (new ArrayList (…). );
The iterators returned by this class’s iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator’s own remove or add methods, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future. The iterator method of this class and the iterator returned by the listIterator method are fail-fast: If after the iterator is to create this list has been changed in the structure, unless it is through the iterator method of remove or add the iterator will throw ConcurrentModificationException. Therefore, in the face of concurrent modification, the iterator fails quickly and simply, rather than risk arbitrary and uncertain behavior at some indeterminate time in the future.
Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs. Note: The fact that the fail-fast behavior of an iterator cannot be guaranteed is, in general, impossible to make any strict guarantees when asynchronous concurrent modifications occur. Fail – fast iterator throw ConcurrentModificationException as best as you can. Therefore, it would be wrong to write a program based on the correctness of this exception: the fail-fast behavior should only be used to locate the problem.
2. ElementData is not serialized
transient Object[] elementData;
Copy the codeIn the case of variable declarations, the data stored by elementData is not saved if an ArrayList instance is serialized. In practice, objects returned by apis exposed at the back end often contain ArrayList. How is this data passed? The specific situation needs to be verified.
3. Expand the internal array elementData
private static final int DEFAULT_CAPACITY = 10;
Copy the codeThe default capacity is 10.
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
// minCapacity is usually close to size, so this is a win:
elementData = Arrays.copyOf(elementData, newCapacity);
}
Copy the codeAfter automatic expansion, the capacity is 1.5 times the original capacity.
The system also checks whether automatic capacity expansion is sufficient. If not, the system expands the specified capacity.
The Enrecapacity method mentioned in the class comment also ends up calling this grow method. Of course, the need for expansion will be judged first.
public void ensureCapacity(int minCapacity);
Copy the code4. The subList method
Calling the subList method returns an instance of the private inner class subList, indexing only part of the original ArrayList instance. Add, remove and other operations to modify the internal array structure are not provided. Use with caution.
For details, see juejin.cn/post/696606…