資訊專欄INFORMATION COLUMN
摘要：對(duì)于一維數(shù)組來說，這種復(fù)制屬性值傳遞，修改副本不會(huì)影響原來的值。主要先生成一個(gè)等類型的數(shù)組，然后調(diào)用
版本jdk1.7
常用方法
增
public boolean add(E e) {
ensureCapacityInternal(size + 1); // Increments modCount!!
elementData[size++] = e;
return true;
}
public void add(int index, E element) {
rangeCheckForAdd(index);
ensureCapacityInternal(size + 1); // Increments modCount!!
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
elementData[index] = element;
size++;
}
public boolean addAll(Collection c) {
Object[] a = c.toArray();
int numNew = a.length;
ensureCapacityInternal(size + numNew); // Increments modCount
System.arraycopy(a, 0, elementData, size, numNew);
size += numNew;
return numNew != 0;
}
public boolean addAll(int index, Collection c) {
rangeCheckForAdd(index);
Object[] a = c.toArray();
int numNew = a.length;
ensureCapacityInternal(size + numNew); // Increments modCount
int numMoved = size - index;
if (numMoved > 0)
System.arraycopy(elementData, index, elementData, index + numNew,
numMoved);
System.arraycopy(a, 0, elementData, index, numNew);
size += numNew;
return numNew != 0;
}
擴(kuò)容算法
現(xiàn)將容量擴(kuò)充到原來的1.5倍，如果大于需求容量，則新容量為1.5倍的原容量，否則為需求容量
private void ensureCapacityInternal(int minCapacity) {
// 如果容器為空，則比較初始化容量和需要的容量，取大值
if (elementData == EMPTY_ELEMENTDATA) {
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);
}
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// overflow-conscious code
// 如果需要的容量大于當(dāng)前容量，擴(kuò)容
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
// 新容量為原容量的1.5倍
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);
}
再說一下這兩個(gè)函數(shù)Arrays.copy()和System.arraycopy()
System中提供了一個(gè)native靜態(tài)方法arraycopy(),可以使用這個(gè)方法來實(shí)現(xiàn)數(shù)組之間的復(fù)制。對(duì)于一維數(shù)組來說，這種復(fù)制屬性值傳遞，修改副本不會(huì)影響原來的值。對(duì)于二維或者一維數(shù)組中存放的是對(duì)象時(shí)，復(fù)制結(jié)果是一維的引用變量傳遞給副本的一維數(shù)組，修改副本時(shí)，會(huì)影響原來的數(shù)組。
