java中对ArrayList进行排序

ava如何对ArrayList中对象按照该对象某属性排序
（从小到大）
两种方法：


[tr=none]

方法一：<br data-filtered="filtered">Comparator<KNNNode> comparator = new Comparator<KNNNode>() {         @Override        public int compare(KNNNode o1, KNNNode o2) {            System.out.println("进入 compare function");            // TODO Auto-generated method stub            if (o1.getDistance() <= o2.getDistance()) {//o1属性小于等于o2属性时，返回1                return 1;            } else {                return -1;            }        }     };

调用方法：


[tr=none] List<KNNNode> nodelist = new ArrayList<KNNNode>();//此处需要填充nodelist.add();Collections.sort(nodelist, comparator);// 调用





[tr=none] 方法二：<br>class SortBy implements Comparator {        public int compare(Object obj1, Object obj2) {            KNNNode point1 = (KNNNode) obj1;            KNNNode point2 = (KNNNode) obj2;            if (point1.getDistance() <= point2.getDistance()) {                return 1;            } else {                return 0;            }        }    }

调用方法：


[tr=none] Collections.sort(nodelist, new SortBy());
KNNNode结点内的属性：


[tr=none] package newKNN; /** * KNN结点类，用来存储最近邻的k个元组相关的信息 */public class KNNNode {    private int index; // 元组标号    private double distance; // 与测试元组的距离    private String seq;//滑动窗口motif序列片段         public KNNNode(int index, double distance, String seq) {        super();        this.index = index;        this.distance = distance;        this.seq = seq;             }    public int getIndex() {        return index;    }    public void setIndex(int index) {        this.index = index;    }    public double getDistance() {        return distance;    }    public void setDistance(double distance) {        this.distance = distance;    }    public String getSeq() {        return seq;    }    public void setSeq(String seq) {        this.seq = seq;    }     }
我想要按照KNNNode的distance属性排序。


若要按照从大到小的顺序排序，如果只是将
>=返回值改为-1
<返回值改为1 会出现异常。
Comparison method violates its general contract!
原因是是实现接口Comparator 的类有问题 ， 在compare中没有处理好两个比较的对象相等的情况
public int compare(KNNNode o1, KNNNode o2）;即 o1.getDistance() == o2.getDistance() 时，返回值不是0
我最终的实现代码是：（从大到小排序）


[tr=none] Comparator<KNNNode> comparator = new Comparator<KNNNode>() {         @Override        public int compare(KNNNode o1, KNNNode o2) {            // TODO Auto-generated method stub            if (o1.getDistance() < o2.getDistance()) {                return 1;            } else if(o1.getDistance() > o2.getDistance()){                return -1;            }else{                return 0;            }        }     };