List多个字段排序、去重

1、List多个字段排序

    List集合排序是通过java.util.Collections中的sort方法实现的，我们现在的业务场景是：根据List集合中实体bean里面的多个属性字段排序

    首先写一个sort方法的比较器MyComparator

public class MyComparator  implements Comparator<Object> {

@Override
public int compare(Object o1, Object o2) {
CompanyData com1 = (CompanyData) o1;
CompanyData com2 = (CompanyData) o2;
if (com1.getMemlevel().compareTo(com2.getMemlevel()) != 0){ //如果会员等级不一样
        return com1.getMemlevel().compareTo(com2.getMemlevel());
} else if (com1.getCreditLevel().compareTo(com2.getCreditLevel())!=0) {//如果信用等级不一样
     return com1.getCreditLevel().compareTo(com2.getCreditLevel());
} else {//按积分
return com1.getIntegral().compareTo(com2.getIntegral());
}
}

}

    然后调用排序

//按会员等级、信用等级、积分排序
Collections.sort( list, new MyComparator());

2、list集合去重

//去掉重复
public List<CompanyData> removeRepeat(List<CompanyData> all,List<CompanyData> sub){
if (all.size()==0 && sub.size()!=0) {
return sub;
}
for (CompanyData companyData : sub) {
all.add(companyData);
}
Set<Integer> set = new HashSet<Integer>();  
List<CompanyData> newList = new ArrayList<CompanyData>();  
for (Iterator<CompanyData> iter = all.iterator(); iter.hasNext();) {  
CompanyData element = (CompanyData) iter.next();  
       if (set.add(element.getBelong()))  
           newList.add(element);  
    }  
    return newList;  
}

因为set集合只能添加不重复的元素，根据这个特点可以排除掉list集合中的重复元素