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public class Array<E> {
private E[] data;
private int size;
public Array(int capacity){
data = (E[])new Object[capacity]; //不能直接new一个泛型数组,需要先new一个Object数组再强转为泛型数组。
}
public Array(){
this(10);
}
public int getSize(){
return size;
}
public int getCapacity(){
return data.length;
}
public boolean isEmpty(){
return size==0;
}
public void add(int index, E e){
if (index <0 || index>size){
throw new IllegalArgumentException("Add failed! Require index>=0 and index<=size.");
}
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 E get(int index){
if (index<0 || index>=size){
throw new IllegalArgumentException("Get failed! Index is illegal.");
}
return data[index];
}
public void set(int index, E e){
if(index<0 || index>=size){
throw new IllegalArgumentException("Set failed! Index is illegal.");
}
data[index]=e;
}
public boolean contains(E e){
for (int i=0; i<size; i++){
if (data[i].equals(e)){
return true;
}
}
return false;
}
public int find(E e) {
for (int i=0; i<size; i++){
if(data[i].equals(e)){
return i;
}
}
return -1;
}
//删除索引为index的元素,并返回被删除的元素
public E remove(int index){
if(index<0 || index>=size){
throw new IllegalArgumentException("Remove failed! Index is illegal.");
}
E ret=data[index];
for (int i=index+1; i<size; i++){
data[i-1]=data[i]; //尽量不要使用data[i]=data[i+1] i+1可能会发生数组越界
}
size--;
data[size]=null; //无用的游离状态元素
if(size==data.length/4 && data.length/2!=0){ //采用更lazy的方法,防止在size=capacity时来回加减元素时发生复杂度震荡的情况。
resize(data.length/2);
}
return ret;
}
public E removeFirst(){
return remove(0);
}
public E removeLast(){
return remove(size-1);
}
public void removeElement(E e){
int index=find(e);
if(index!=-1){
remove(index);
}
}
//实现动态数组
private void resize(int newCapacity){
E[] newData=(E[])new Object[newCapacity];
for(int i=0; i<size; i++){
newData[i]=data[i];
}
data=newData; //newData在函数退出后会被回收,data是全局变量,生存周期和类一样
}
@Override
public String toString(){
StringBuilder res = new StringBuilder();
res.append(String.format("Array: size: %d, capacity: %d\n",size, data.length));
res.append("[");
for (int i=0; i<size; i++){
res.append(data[i]);
if (i!=size-1){
res.append(", ");
}
}
res.append("]");
return res.toString();
}
}