链表List

当要创建一个链表的时候，首先要创建一个节点类，在Java里面叫条目（entry表示），这个类是一个嵌套类，里面包含三个要素，element， next， previous。

public class Link<E> {

private static class Entry<E> {
private E element;

private Entry<E> next;

private Entry<E> previous;


public Entry(E e, Entry<E> next , Entry<E> previous) {
this.element = e;
this.next = next;
this.previous = previous;
}
}
}

创建一个头结点和初始头结点，另外增加一个size用来统计节点数

public class Link<E> {

private transient Entry<E> header = new Entry<E>(null, null, null);
private transient int size = 0;

/**
* Constructs an empty list.
*/
public Link() {
header.next = header.previous = header;
}

private static class Entry<E> {
private E element;

private Entry<E> next;

private Entry<E> previous;


public Entry(E e, Entry<E> next , Entry<E> previous) {
this.element = e;
this.next = next;
this.previous = previous;
}
}
}

添加和获取、删除节点

package com.hyd.link;

import java.util.NoSuchElementException;

public class Link<E> {

private transient Entry<E> header = new Entry<E>(null, null, null);
private transient int size = 0;

/**
* Constructs an empty list.
*/
public Link() {
header.next = header.previous = header;
}

public int size() {
return this.size;
}

public boolean add(E e) {
addBefore(e, header);
return true;
}

public E get(int index) {
return entry(index).element;
}

public E remove(int index) {
return remove(entry(index));
}

private Entry<E> addBefore(E e, Entry<E> entry) {
Entry<E> newEntry = new Entry<E>(e, entry, entry.previous);
newEntry.previous.next = newEntry;
newEntry.next.previous = newEntry;
size ++;
return newEntry;
}

/**
* Returns the indexed entry.
*/
private Entry<E> entry(int index) {
if (index < 0 || index > size) {
throw new IndexOutOfBoundsException("Index: " + index +
", Size: " + size);
}

Entry<E> e = header;
if (index < (size >> 1)) {
for (int i = 0; i <= index; i++)
e = e.next;
} else {
for (int i = size; i > index; i--)
e = e.previous;
}


return e;
}

private E remove(Entry<E> e) {
if (e == header)
throw new NoSuchElementException();

E result = e.element;
e.previous.next = e.next;
e.next.previous = e.previous;
e.next = e.previous = null;
e.element = null;
size--;
return result;
}

private static class Entry<E> {
private E element;

private Entry<E> next;

private Entry<E> previous;


public Entry(E e, Entry<E> next , Entry<E> previous) {
this.element = e;
this.next = next;
this.previous = previous;
}
}
}