list排序,该怎么处理

import java.util.Comparator;public class CoComparator implements Comparator {    @Override    public int compare(Object a0, Object a1) {    Student s1 =(Student) a0;    Student s2 = (Student) a1;         if (s1.getSum()<s2.getSum()){             return 1;         }else{             return 0;         }    }    }

]import java.util.ArrayList;import java.util.Iterator;import java.util.Collections;public class Test {    public static void main(String[] args) {        Student s1 = new Student("haha",1,12,13);        Student s2 = new Student("xixi",2,11,15);        Student s3 = new Student("wowo",3,10,14);                ArrayList a = new ArrayList();        a.add(s1);        a.add(s2);        a.add(s3);                CoComparator co = new CoComparator();        Collections.sort(a,co);                        Iterator it = a.iterator();        Student ss;                while(it.hasNext()){        ss=(Student)it.next();        System.out.println(ss.name+"   "+ss.id+"    "+ss.getSum());        }                    }[/code[code=Java]public class Student {    String name;    int id;    double math;    double english;    double sum;        public Student(String name, int id, double math, double english) {        this.name = name;        this.id = id;        this.math = math;        this.english = english;    }    public double getSum() {        return sum=math+english;    }}

    /**     * Compares two <code>Integer</code> objects numerically.     *     * @param   anotherInteger   the <code>Integer</code> to be compared.     * @return    the value <code>0</code> if this <code>Integer</code> is     *         equal to the argument <code>Integer</code>; a value less than     *         <code>0</code> if this <code>Integer</code> is numerically less     *         than the argument <code>Integer</code>; and a value greater      *         than <code>0</code> if this <code>Integer</code> is numerically     *          greater than the argument <code>Integer</code> (signed     *          comparison).     * @since   1.2     */    public int compareTo(Integer anotherInteger) {    int thisVal = this.value;    int anotherVal = anotherInteger.value;    return (thisVal<anotherVal ? -1 : (thisVal==anotherVal ? 0 : 1));    }