1 结构:List-》AbstractList-》ArrayList,LinkedList
package 链表;
public interface List<E> {
//默认公共
static final int ELEMENT_NOT_FOUND = -1;
/**
* 清除所有元素
*/
void clear();
/**
* 元素的数量
*/
int size();
/**
* 是否为空
*/
boolean isEmpty();
/**
* 是否包含某个元素
*/
boolean contains(E element);
/**
* 添加元素到尾部
* @param element
*/
void add(E element);
/**
* 获取index位置的元素
*/
E get(int index);
/**
* 设置index位置的元素
*/
E set(int index, E element);
/**
* 在index位置插入一个元素
*/
void add(int index, E element);
/**
* 删除index位置的元素
*/
E remove(int index);
/**
* 查看元素的索引
*/
int indexOf(E element);
}
package 链表;
public abstract class AbstractList<E> implements List<E>{
/**
* 元素的数量
*/
protected int size;
/**
* 元素的数量
*/
public int size() {
return size;
}
/**
* 是否为空
*/
public boolean isEmpty() {
return size == 0;
}
//封装报错
protected void outOfBounds(int index) {
throw new IndexOutOfBoundsException("Index"+index+",Size:"+size);
}
protected void rangeCheck(int index) {
if(index<0||index>=size) {
outOfBounds(index);
}
}
protected void rangeCheckForAdd(int index) {
if(index<0||index>size) {
outOfBounds(index);
}
}
/**
* 是否包含某个元素
*/
public boolean contains(E element) {
return indexOf(element)!=ELEMENT_NOT_FOUND;
}
/**
* 添加元素到尾部
*/
public void add(E element) {
add(size,element);
}
}
package 链表;
public class LinkedList<E> extends AbstractList<E>{
// 因为继承自AbstractList,所以不需要:private int size;否则会报越界异常
//头结点
private Node<E> first;
private static class Node<E> {
E element;
Node<E> next;
public Node(E element,Node<E> next) {
this.element = element;
this.next = next;
}
}
public void clear() {
size = 0;
first = null;
}
public int size() {
return size;
}
public boolean isEmpty() {
return size == 0;
}
public boolean contains(E element) {
return indexOf(element)!=ELEMENT_NOT_FOUND;
}
public E get(int index) {
return node(index).element;
}
public E set(int index, E element) {
Node<E> node = node(index);
E oldE = node.element;
node.element = element;
return oldE;
}
public void add(int index, E element) {
if(index == 0) {
System.out.println("已进入");
first = new Node<>(element, first);
}else {
Node<E> preNode = node(index-1);
//将结点2插入结点1和结点3中间:先让结点2指向结点3,然后让结点1指向结点2!!!
preNode.next = new Node<>(element, preNode.next);
}
size++;
}
public E remove(int index) {
rangeCheck(index);
Node<E> node = first;
if (index == 0) {
first = first.next;
}else {
Node<E> preNode = node(index-1);
node = preNode.next;
preNode.next = node.next;
}
size--;
return node.element;
}
public int indexOf(E element) {
if(element==null) {
Node<E> node = first;
for (int i = 0; i < size; i++) {
if (node.element == null) {return i;}
node = node.next;
}
}else {
Node<E> node = first;
for(int i=0;i<size;i++) {
if(element.equals(node.element)) return i;
node = node.next;
}
}
return ELEMENT_NOT_FOUND;
}
/**
* @Description:获取index位置对应结点对象
*/
private Node<E> node(int index) {
rangeCheck(index);
Node<E> node = first;
for (int i = 0; i < index; i++) {
node = node.next;
}
return node;
}
public String toString() {
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append("size=").append(size).append(",[");
Node<E> node = first;
for (int i = 0; i < size; i++) {
if(i!=0) {
stringBuilder.append(",");
}
stringBuilder.append(node.element);
node = node.next;
}
stringBuilder.append("]");
// Node<E> node1 = first;
// while(node1!=null) {
// node1 = node1.next;
// }
return stringBuilder.toString();
}
}
package 链表;
//消除警告
@SuppressWarnings("unchecked")
public class ArrayList<E> extends AbstractList<E>{
/**
* 所有的元素
*/
private E[] elements;
private static final int DEFAULT_CAPACITY = 10;
//初始化数组
public ArrayList(int capaticy) {
capaticy = (capaticy<DEFAULT_CAPACITY)?DEFAULT_CAPACITY:capaticy;
//因为所有类都继承自object,所以先new Object数组,再强转
elements = (E[])new Object[capaticy];
}
//无参数则默认大小为10
public ArrayList() {
//调用有参的构造函数!!!
this(DEFAULT_CAPACITY);
}
/**
* 清除所有元素
*/
public void clear() {
for (int i = 0; i < size; i++) {
elements[i] = null;
}
//不能用:elements = null; 因为会断掉数组(栈)指向堆的空间,堆内部东西会销毁,每次都需要重新开辟空间。
size = 0;
}
/**
* 获取index位置的元素
*/
public E get(int index) {
rangeCheck(index);
return elements[index];
}
/**
* 设置index位置的元素
* @return 历史的元素
*/
public E set(int index,E element) {
rangeCheck(index);
E old = elements[index];
elements[index] = element;
return old;
}
/**
* 在index位置插入一个元素
*/
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++;
}
/**
* 删除index位置的元素
*/
public E remove(int index) {
rangeCheck(index);
E old = elements[index];
for (int i = index+1; i < size; i++) {
elements[i-1] = elements[i];
}
elements[--size]=null;
return old;
}
/**
* 查看元素的位置
*/
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(elements[i].equals(element)) return i;
}
}
return ELEMENT_NOT_FOUND;
}
/**
* 数组转换成字符串
*/
@Override
public String toString() {
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append("size=").append(size).append(",[");
for (int i = 0; i < size; i++) {
if(i!=0) {
stringBuilder.append(",");
}
stringBuilder.append(elements[i]);
// if(i!=size-1) {
// stringBuilder.append(",");
// }
}
stringBuilder.append("]");
return stringBuilder.toString();
}
/**
* @Description:保证容量至少有capacity
*/
private void ensureCapacity(int capacity) {
int oldCapacity = elements.length;
if(oldCapacity>=capacity) return;
//新容量为旧容量的1.5倍
int newCapacity = oldCapacity+(oldCapacity>>1);
E[] newElements = (E[])new Object[newCapacity];
//将原数组的元素填入新数组
for (int i = 0; i < size; i++) {
newElements[i] = elements[i];
}
//原数组指向新数组
elements = newElements;
System.out.println("扩容:"+oldCapacity+"至"+newCapacity);
}
}
2 虚拟头结点:减少头结点与其他结点操作差异
package 链表;
/**
* 增加虚拟头结点
*/
public class LinkedList2<E> extends AbstractList<E>{
private Node<E> first;
//虚拟头结点
public LinkedList2() {
first = new Node<>(null, null);
}
...
public void add(int index, E element) {
rangeCheckForAdd(index);
Node<E> preNode = index == 0?first:node(index-1);
preNode.next = new Node<>(element, preNode.next);
size++;
}
public E remove(int index) {
rangeCheck(index);
Node<E> preNode = index == 0?first:node(index-1);
Node<E> node = preNode.next;
preNode.next = node.next;
size--;
return node.element;
}
...
}