动态数组（java）

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);}@Overridepublic int size() {return size;}@Overridepublic boolean isEmpty() {return size == 0;}@Overridepublic boolean contains(E element) {return indexOf(element) != ELEMENT_NOT_FOUND;}@Overridepublic void add(E element) {add(size,element);}@Overridepublic E get(int index) {rangeCheck(index);return elements[index];}@Overridepublic E set(int index, E element) {rangeCheck(index);E old = elements[index];elements[index] = element;return old;}@Overridepublic 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 ++;}@Overridepublic 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;}@Overridepublic 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;}@Overridepublic 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);}@Overridepublic 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 {@Testpublic 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：