Java集合類-ArrayList分析
阿新 • • 發佈：2017-10-11
empty java 如果 all ansi code ati class des
ArrayList的特點
可以動態擴容 非線程安全 支持序列化 線程安全的List Collections.synchronizedList、CopyOnWriteArrayList成員變量
private static final int DEFAULT_CAPACITY = 10; // 初始大小 transient Object[] elementData; // 存儲元素的數組 private int size; //容器大小基本方法
增 add
public boolean add(E e) { ensureCapacityInternal(size + 1); //Increments modCount!! elementData[size++] = e; return true; }
private void ensureCapacityInternal(int minCapacity) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);
}
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// overflow-conscious code
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
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);
}
刪 remove
改 set
查 get
ArrayList擴容原理
如果新加入元素後數組容量不夠需要進行擴容，執行grow方法
默認擴容為之前的1.5倍，如果容量不夠則直接擴充為加入當前元素後的大小
然後利用Arrays.copyOf進行數組的復制
相關類和方法
Arrays.copyOf()
System.arraycopy()
public static native void arraycopy(
Object src,
int srcPos,
Object dest,
int destPos,
int length
);
Java集合類-ArrayList分析