对有序list分组

faulware

近来要对一个有序的list进行分组，由于我是初学者，以前没有编程经验，所以出了许多bug。下面分享一下。

    List里面放着author，author有属性id、name和writeCount三个属性，分别表示作者id、昵称和编辑文章数量。对于按照id排序的list，统计每个作者编辑了多少文章。
public class author
{
    private  int id;
    private String name;
    private int writeCount;
//set get 方法
}
   List的初始值是：original list
author id=1 author name=1ligang
author id=2 author name=2ligang
author id=2 author name=2ligang
author id=3 author name=3ligang
author id=3 author name=3ligang
author id=3 author name=3ligang
author id=4 author name=4ligang
author id=4 author name=4ligang
author id=4 author name=4ligang
author id=4 author name=4ligang
   开始我想都没有想打算用2个for循环遍历，可是后面就出现了bug。哈哈，死循环.....代码如下：
  public void groupList(List<author> list)
    {
if(list==null || list.size()==0)
{
    return;
}
List<author> resultList=new ArrayList<author>();
int tempWriteCount=1;
author tempAuthor=new author();
for(int i=0;i<list.size();i++)
{
    //tempAuthor=list.get(i);
    for(int j=1;j<list.size();j++)
    {
if(list.get(i).getId()==list.get(j).getId())
{
    tempWriteCount+=1;
}else {
    tempAuthor.setWriteCount(tempWriteCount);
    resultList.add(tempAuthor);
    tempWriteCount=1;
    i=j;
   
}
    }
}
tempAuthor.setWriteCount(tempWriteCount);
resultList.add(tempAuthor);

for(author temp:resultList)
{
    System.out.println("id="+temp.getId()+" name="+temp.getName()+" write "+temp.getWriteCount()+" book");
}
    }
结果出错，Exception in thread "main" java.lang.OutOfMemoryError: Java heap space。自己想想就算是i=j没执行，也只执行10*10次不至于没存耗尽。最后发现在i=j处出现了问题，让i永远都小于10，出错。囧
后来改了下：
public void groupList(List<author> list)
    {
if(list==null || list.size()==0)
{
    return;
}
List<author> resultList=new ArrayList<author>();
int tempWriteCount=1;
author tempAuthor=new author();
for(int i=0;i<list.size();i++)
{
    tempAuthor=list.get(i);
    for(int j=i+1;j<list.size();)
    {
if(tempAuthor.getId()==list.get(j).getId())
{
    tempWriteCount+=1;
    break;
}else {
    tempAuthor.setWriteCount(tempWriteCount);
    resultList.add(tempAuthor);
    tempWriteCount=1;
    i=j;
    break;
   
}
    }
}
tempAuthor.setWriteCount(tempWriteCount);
resultList.add(tempAuthor);

for(author temp:resultList)
{
    System.out.println("id="+temp.getId()+" name="+temp.getName()+" write "+temp.getWriteCount()+" book");
}
    }
运行结果
id=1 name=1ligang write 1 book
id=2 name=2ligang write 1 book
id=3 name=3ligang write 2 book
id=4 name=4ligang write 3 book
分组对了，计算结果不对。
    改进时候将i=j;改为i=j-1;。成功。
   再后来一想，只用遍历一遍list比较相邻的id是否相同即可。代码如下：
   public void groupList(List<author> list)
    {
if (list == null || list.size() == 0)
    return;
int tempWriterCount=1;
author tempAuthor = new author();
List<author> resultList = new ArrayList<author>();
for (int i = 0; i < list.size()-1; i++)
{
   
   
    tempAuthor = list.get(i);//get i
    if(tempAuthor.getId()==list.get(i+1).getId())
    {
tempWriterCount+=1;
    }else {
tempAuthor.setWriteCount(tempWriterCount);
resultList.add(tempAuthor);
tempAuthor=new author();
tempWriterCount=1;
    }
   }
tempAuthor.setWriteCount(tempWriterCount);
resultList.add(tempAuthor);//add the last one
System.out.println("after group:");
for (author temp : resultList)
{
    temp.setAuthorCount(resultList.size());
   
    System.out.println(temp.getId()+" "+temp.getName()+" "+temp.getWriteCount());
}

    }
  最后还可以用List<List<author>>来分组，代码如下：
   public void groupOrderedList(List<author> list)
    {
List<List<author>> tempList = new ArrayList<List<author>>();
List<author> group = new ArrayList<author>();

List<author> displayList=new ArrayList<author>();
author temp = list.get(0);
group.add(temp);
for(int i=1;i<list.size();i++)
{
    if(temp.getId()==list.get(i).getId())
    {
group.add(temp);
    }else {
tempList.add(group);
temp=list.get(i);
group=new ArrayList<author>();
group.add(temp);
    }
}


tempList.add(group);

for (List<author> tempDisplayList : tempList)
{
    author displayAuthor=new author();
    displayAuthor=tempDisplayList.get(0);
    displayAuthor.setWriteCount(tempDisplayList.size());
    displayList.add(displayAuthor);
}

System.out.println("grouped list:");
for(author tempAuthor:displayList)
{
    System.out.println(tempAuthor.getId()+" "+tempAuthor.getName()+" "+tempAuthor.getWriteCount());
}

System.out.println("total author is "+displayList.size());
    }