package arraList;
public interface AbstractArray<E> {
int size();//元素数量
boolean isEmpty();//是否为空
boolean contains(E element);//是否包含某个元素
void add(E element);//添加元素到最后面
E get(int index);//返回index位置对应的元素
E set(int index,E element);//设置index位置的元素
void add(int index,E element);//往index位置添加元素
E remove(int index);//删除index位置对应的元素
int indexOf(E element);//查看元素的位置
void clear();//清除所有元素
}
package arraList;
public class ArrayList<E> implements AbstractArray<E> {
private int size;
private E[] elements;
private static final int DEFAULT_CAPACITY = 10;
private static final int ELEMENT_NOT_FOUND = -1;
public ArrayList(int capacity){
capacity = (capacity < DEFAULT_CAPACITY) ? DEFAULT_CAPACITY :capacity;
elements =(E[]) new Object[capacity];
}
public ArrayList(){
this(DEFAULT_CAPACITY);
}
@Override
public int size() {
return size;
}
@Override
public boolean isEmpty() {
return size == 0;
}
@Override
public boolean contains(E element) {
return indexOf(element) != ELEMENT_NOT_FOUND;
}
@Override
public void add(E element) {
add(size,element);
}
@Override
public E get(int index) {
rangeCheck(index);
return elements[index];
}
@Override
public E set(int index, E element) {
rangeCheck(index);
E old = elements[index];
elements[index] = element;
return old;
}
@Override
public void add(int index, E element) {
rangeCheckForAdd(index);
ensureCapacity(size + 1);
for(int i = size - 1;i >= index;i --){
elements[i + 1] = elements[i];
}
elements[index] = element;
size ++;
}
@Override
public E remove(int index) {
E old = elements[index];
for (int i = index + 1; i <= size; i++) {
elements[i - 1] = elements[i];
}
elements[--size] = null;
return old;
}
@Override
public int indexOf(E element) {
if(element == null){
for (int i = 0; i < size; i++) {
if(elements[i] == null)return i;
}
}else{
for (int i = 0; i < size; i++) {
if(element.equals(elements[i])) return i;
}
}
return ELEMENT_NOT_FOUND;
}
@Override
public void clear() {
for (int i = 0; i < size; i++) {
elements[i] = null;
}
size = 0;
}
private void ensureCapacity(int capacity){
int oldCapacity = elements.length;
if(oldCapacity >= capacity) return;
int newCapacity = oldCapacity + (oldCapacity >> 1);
E[] newElements = (E[]) new Object[newCapacity];
for (int i = 0; i < size; i++) {
newElements[i] = elements[i];
}
elements = newElements;
}
private void rangeCheckForAdd(int index){
if(index < 0 || index > size) throw new IndexOutOfBoundsException("Index:"+ index +",Size"+size);
}
private void rangeCheck(int index){
if(index < 0 || index >= size) throw new IndexOutOfBoundsException("Index:"+ index +",Size" + size);
}
@Override
public String toString() {
StringBuilder string = new StringBuilder();
string.append("size=").append(size).append(", [");
for (int i = 0; i < size; i++) {
if(i != 0){
string.append(", ");
}
string.append(elements[i]);
}
string.append("]");
return string.toString();
}
}
测试
public class test {
@Test
public void test(){
ArrayList<Integer> lists = new ArrayList<>();
lists.add(1);
lists.add(2);
System.out.println(lists);
ArrayList<Person> persons = new ArrayList<>();
persons.add(new Person("jack",10));
persons.add(new Person("james",21));
persons.add(new Person("rose",18));
persons.add(null);
System.out.println(persons);
System.out.println(persons.indexOf(null));
}
}
重点:
- 动态数组的扩容机制
- 泛型
- indexOf() 方法判断是否相等,equals() 和 == 区别
- 添加、删除:移动元素