Java实现单链表

package list;

/**
 * 节点
 * 
 * @author DeepSleeping
 *
 */
public class ListNode {

    Object data;
    ListNode next;

    public ListNode(Object data) {
        super();
        this.data = data;
    }
}

package list;

/**
 * 单链表
 * 
 * @author DeepSleeping
 *
 */
public class SingleList implements MyList {

    private ListNode first;
    private ListNode last;
    private int size;
    
    @Override
    public void add(Object element) {
        if (first == null) {
            first = new ListNode(element);
            last = first;
        }else{
            last.next = new ListNode(element);
            last = last.next;
        }
        size++;
    }

    @Override
    public void delete(Object element) {
        ListNode p = first;
        ListNode pre = null;
        while(p != null){
            if (p.data.equals(element)) {
                //如果删除的是第一个元素
                if (p == first) {
                    first = first.next;
                }else{
                    pre.next = p.next;
                }
                break; //注意，删除了第一个相同的元素之后应该跳出循环
            }
            pre = p;
            p = p.next;
        }
        size--;
    }

    @Override
    public void delete(int index) {
        if (index < 0 || index >= size) {
            return;
        }
        int i = 0;//指针指向的节点的索引
        ListNode p = first;
        ListNode pre = null;
        while(p != null){
            if (i == index) {
                if (p == first) {
                    first = first.next;
                }
                else{
                    pre.next = p.next;
                }
                break;
            }
            pre = p;
            p = p.next;
            i++;
        }
        size--;
    }

    @Override
    public void update(int index, Object newElement) {
        int i = 0;//指针指向的节点的索引
        ListNode p = first;
        while(p != null){
            if (i == index) {
                p.data = newElement;
            }
            p = p.next;
            i++;
        }
    }

    @Override
    public boolean contains(Object target) {
        ListNode p = first;
        while(p != null){
            if (p.data.equals(target)) {
                return true;
            }
            p = p.next;
        }
        return false;
    }

    @Override
    public Object at(int index) {
        if (index < 0 || index >= size) {
            return null;
        }
        int i = 0;//指针指向的节点的索引
        ListNode p = first;
        while(p != null){
            if (i == index) {
                return p.data;
            }
            p = p.next;
            i++;
        }
        return null;
    }

    @Override
    public int indexOf(Object element) {
        int i = 0;
        ListNode p = first;
        
        while(p != null){
            if (p.data.equals(element)) {
                return i;
            }
            p = p.next;
            i++;
        }
        return -1;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder("[");
        ListNode p = first;
        while(p != null){
            sb.append(p.data);
            if (p.next != null) {
                sb.append(",");
            }
            
            p = p.next;    
        }
        sb.append("]");
        return sb.toString();
    }
}