动态数组
2018-07-16 本文已影响15人
GeekAmI
- 手动实现版本
public class Array<E> {
private E[] data;
private int size;
public Array(int capacity) {
data = (E[]) new Object[capacity];
size = 0;
}
public Array() {
this(10);
}
public void add(int index, E e) {
if (index < 0 || index > size) {
throw new RuntimeException("Illegal index, index should in[0, size]!");
}
//动态扩容
if (size >= data.length) {
resize(2 * data.length);
}
for (int i = size - 1; i >= index; i--) {
data[i + 1] = data[i];
}
data[index] = e;
size++;
}
public void addFirst(E e) {
add(0, e);
}
public void addLast(E e) {
add(size, e);
}
public int find(E e) {
for (int i = 0; i < size; i++) {
if (data[i].equals(e)) {
return i;
}
}
return -1;
}
public boolean contains(E e) {
for (int i = 0; i < size; i++) {
if (data[i].equals(e)) {
return true;
}
}
return false;
}
public E get(int index) {
if (index < 0 || index >= size) {
throw new RuntimeException("Illegal index, index should in[0, size)!");
}
return data[index];
}
public E getFirst() {
return data[0];
}
public E getLast() {
return data[size - 1];
}
public void set(int index, E e) {
if (index < 0 || index >= size) {
throw new RuntimeException("Illegal index, index should in[0, size)!");
}
data[index] = e;
}
public E remove(int index) {
if (index < 0 || index >= size) {
throw new RuntimeException("Illegal index, index should in[0, size)!");
}
E ret = data[index];
for (int i = index + 1; i < size; i++) {
data[i - 1] = data[i];
}
size--;
// azy缩容
if (size == data.length / 4 && data.length / 2 != 0) {
resize(data.length / 2);
}
return ret;
}
public E removeFirst() {
return remove(0);
}
public E removeLast() {
return remove(size - 1);
}
public void remove(E e) {
int index = find(e);
if (index != -1) {
remove(index);
}
}
public int getCapacity() {
return data.length;
}
public boolean isEmpty() {
return size == 0;
}
public int getSize() {
return size;
}
private void resize(int newCapacity) {
if (newCapacity < size) {
throw new RuntimeException("Illegal newCapacity, newCapacity should >= size");
}
E[] newData = (E[]) new Object[newCapacity];
for (int i = 0; i < size; i++) {
newData[i] = data[i];
}
data = newData;
}
@Override
public String toString() {
StringBuilder res = new StringBuilder();
res.append("Array size:" + size + ", capacity:" + data.length + "\n");
res.append("data[");
for (int i = 0; i < size; i++) {
res.append(data[i] + " ");
}
res.append("]");
return res.toString();
}
}
- JDK版本分析
2.1 需要扩容时,变为原来的1.5倍
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);
}
2.2 通过垃圾回收,动态缩容
public E remove(int index) {
rangeCheck(index);
modCount++;
E oldValue = elementData(index);
int numMoved = size - index - 1;
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
elementData[--size] = null; // clear to let GC do its work
return oldValue;
}
总结:还是JDK写的漂亮啊🤣