对其中某元素进行排序

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class test {

    /**
     * @param args
     * @return
     */

    public static void main(String[] args) {

        TuanInfo tuan1 = new TuanInfo();
        tuan1.setAaa(2);
        tuan1.setBuyer(2);
        TuanInfo tuan2 = new TuanInfo();
        tuan2.setAaa(1);
        tuan2.setBuyer(1);
        TuanInfo tuan3 = new TuanInfo();
        tuan3.setAaa(3);
        tuan3.setBuyer(3);
        List<TuanInfo> list = new ArrayList<TuanInfo>();
        list.add(tuan3);
        list.add(tuan2);
        list.add(tuan1);
        for (TuanInfo t : list) {
            System.out.println(t.getBuyer() + " " + t.getAaa());
        }
        Collections.sort(list, new BuyerCompare());
        for (TuanInfo t : list) {
            System.out.println(t.getBuyer() + " " + t.getAaa());
        }

    }
}

class TuanInfo {
    int buyer;
    int aaa;

    public int getBuyer() {
        return buyer;
    }

    public void setBuyer(int buyer) {
        this.buyer = buyer;
    }

    public int getAaa() {
        return aaa;
    }

    public void setAaa(int aaa) {
        this.aaa = aaa;
    }

}

class BuyerCompare implements Comparator<TuanInfo> {
    public int compare(TuanInfo o1, TuanInfo o2) {
        if (o1.getBuyer() > o2.getBuyer())
            return -1;
        else
            return 1;
    }
}