Java 容器源码分析之 ArrayList（6）
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- UID
- 1066743
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Java 容器源码分析之 ArrayList（6）
上面从ArrayList中移除元素的所有方法中都没有对移除元素后的数组大小进行调整，这种情况下可能会在移除大量元素后造成空间的浪费。这时候可以通过trimToSize方法将数组大小调整为实际的大小。
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| /**
* Trims the capacity of this ArrayList instance to be the
* list's current size. An application can use this operation to minimize
* the storage of an ArrayList instance.
*/
public void trimToSize() {
modCount++;
if (size < elementData.length) {
elementData = (size == 0)
? EMPTY_ELEMENTDATA
: Arrays.copyOf(elementData, size);
}
}
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更新及查找1
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public boolean contains(Object o) {
return indexOf(o) >= 0;
}
/**
* Returns the index of the first occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the lowest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*/
public int indexOf(Object o) {
if (o == null) {
for (int i = 0; i < size; i++)
if (elementData==null)
return i;
} else {
for (int i = 0; i < size; i++)
if (o.equals(elementData))
return i;
}
return -1;
}
/**
* Returns the index of the last occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the highest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*/
public int lastIndexOf(Object o) {
if (o == null) {
for (int i = size-1; i >= 0; i--)
if (elementData==null)
return i;
} else {
for (int i = size-1; i >= 0; i--)
if (o.equals(elementData))
return i;
}
return -1;
}
/**
* Returns the element at the specified position in this list.
*/
public E get(int index) {
rangeCheck(index);
return elementData(index);
}
/**
* Replaces the element at the specified position in this list with
* the specified element.
*/
public E set(int index, E element) {
rangeCheck(index);
E oldValue = elementData(index);
elementData[index] = element;
return oldValue;
}
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基于数组的实现使得更新元素及查找元素变得比较简单。在set方法中不会修改modCount的值。 |
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