java 中对象比较大小

java 中对象比较大小  

java 中对象比较大小有两种方法 
1：实现Comparable 接口 的 public int compareTo(T o) 方法； 

2：实现Comparator 接口 的   int compare(T o1, T o2)方法； 

代码如下： 

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

 public class Test {
     public static void main(String[] args) {
         List list =new ArrayList();
         list.add(new Dept("2","研发部",23));
         list.add(new Dept("2","总公司",575));
         list.add(new Dept("2","总公司",565));
 //      Collections.sort(list);
         Collections.sort(list, new Comparator(){

             public int compare(Object arg0, Object arg1) {
                 // TODO Auto-generated method stub
                 Dept dept1=(Dept)arg0;
                 Dept dept2=(Dept)arg1;
                 return dept1.compareTo(dept2);
             }

         });

         for (int i=0;i
             System.out.println((Dept)list.get(i));
         }


         Dept dept1=new Dept("2","研发部",23);
         Dept dept2=new Dept("2","kk",44);
         Set set=new TreeSet(new Comparator(){

             public int compare(Object arg0, Object arg1) {
                 // TODO Auto-generated method stub
                 return 0;
             }

         });
         set.add(dept1);
         set.add(dept2);


     }
 }

 class Dept implements Comparable{
     private String id;
     private String name;
     private long num;
     public Dept(String id,String name,long num){
         this.id=id;
         this.name=name;
         this.num=num;
     }
     public String getId() {
         return id;
     }

     public void setId(String id) {
         this.id = id;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public long getNum() {
         return num;
     }

     public void setNum(long num) {
         this.num = num;
     }

     public int compareTo(Object arg0) {
         Dept dept=(Dept) arg0;
         int i=0;
         i=this.id.compareTo(dept.id);
         if(i!=0){//部门id不相等
             return i;
         }else{//部门id相等
             i=this.name.compareTo(dept.name);
             if(i!=0){//部门名称不相等
                 return i;
             }else{//部门名称不相等
                 if(this.num>dept.num)return 1;
                 else if(this.numreturn -1;
                 else return 0;
             }
         }

     }
     public String toString() {
         // TODO Auto-generated method stub
         return this.id+"-->"+this.name+"-->"+this.num;
     }

 }