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<list.size();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.num<dept.num)return -1;
                else return 0;
            }
        }  

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

}

原文地址： http://blog.****.net/aerchi/article/details/7921481