List中按照对象的某个字段进行排序

 //按照是否有效对list进行排序
        Collections.sort(retRights, new Comparator<EstateBaseInfo>() {
            @Override
            public int compare(EstateBaseInfo o1, EstateBaseInfo o2) {
                if(o1.getVaildState()>o2.getVaildState()){
                    return 1;
                }
                if(o1.getVaildState()==o2.getVaildState()){
                    return 0;
                }
                return -1;
            }
        });

其中o1代表前一个对象，o2代表后一个对象
如果返回值大于0就将他们互换位置，所以我这里是按照升序排列
反之改为o1.getVaildState()<o2.getVaildState()将可以按照降序排列了

源码：

public static <T> void sort(List<T> list, Comparator<? super T> c) {
    Object[] a = list.toArray();
    Arrays.sort(a, (Comparator)c);
    ListIterator i = list.listIterator();
    for (int j=0; j<a.length; j++) {
        i.next();
        i.set(a[j]);
    }
    }

可以看出程序首先将List转为了Array

public static <T> void sort(T[] a, Comparator<? super T> c) {
    T[] aux = (T[])a.clone();
        if (c==null)
            mergeSort(aux, a, 0, a.length, 0);
        else
            mergeSort(aux, a, 0, a.length, 0, c);
    }

这里判断是否有自定义的Comparator
我们需要自定义比较方式

   private static void mergeSort(Object[] src,
                  Object[] dest,
                  int low, int high, int off,
                  Comparator c) {
    int length = high - low;

    // Insertion sort on smallest arrays
    if (length < INSERTIONSORT_THRESHOLD) {
        for (int i=low; i<high; i++)
        for (int j=i; j>low && c.compare(dest[j-1], dest[j])>0; j--)
            swap(dest, j, j-1);
        return;
    }

        // Recursively sort halves of dest into src
        int destLow  = low;
        int destHigh = high;
        low  += off;
        high += off;
        int mid = (low + high) >>> 1;
        mergeSort(dest, src, low, mid, -off, c);
        mergeSort(dest, src, mid, high, -off, c);

        // If list is already sorted, just copy from src to dest.  This is an
        // optimization that results in faster sorts for nearly ordered lists.
        if (c.compare(src[mid-1], src[mid]) <= 0) {
           System.arraycopy(src, low, dest, destLow, length);
           return;
        }

        // Merge sorted halves (now in src) into dest
        for(int i = destLow, p = low, q = mid; i < destHigh; i++) {
            if (q >= high || p < mid && c.compare(src[p], src[q]) <= 0)
                dest[i] = src[p++];
            else
                dest[i] = src[q++];
        }
    }

private static void swap(Object[] x, int a, int b) {
    Object t = x[a];
    x[a] = x[b];
    x[b] = t;
    }

这里是进行排序的主要方法了
可以看出来对于size()<7的数组直接进行比较运算private static final int INSERTIONSORT_THRESHOLD = 7;
如果前一个指定的值大于后一个的话则直接交换位置