Collections.sort

第一种方法:容器内要排序的类必须时下Comparable接口:  sort ( List list)

例子:
import java.util.*;
public class Main{
public static void main(String args[]){
ArrayList al=new ArrayList();
al.add(new Student(2,"aa"));
al.add(new Student(1,"bb"));
al.add(new Student(3,"dd"));
al.add(new Student(3,"cc"));
Collections.sort(al);
Iterator it=al.iterator();
while(it.hasNext()){
System.out.println(it.next());
}
}
}
class Student implements Comparable{
int id;
String name;
Student(int id,String name){
this.id=id;
this.name=name;
}
public int compareTo(Object o){
Student s=(Student)o;
int result=(id>s.id)?1:((id==s.id)?0:-1);
if(0==result){
result=name.compareTo(s.name);
}
return result;
}
public String toString(){
return "id="+this.id+",name="+this.name;

}
}

 

 

第二种方法:使用静态内部类实现Comparator接口:sort ( List list, Comparator c)

 

只需实现compare方法就行,equals方法在obeject类就会有,而实体类继承自object类,就必然会有equals方法,所以不需实现

例子
import java.util.*;
public class Main{
public static void main(String args[]){
ArrayList al=new ArrayList();
al.add(new Student(2,"aa"));
al.add(new Student(1,"bb"));
al.add(new Student(3,"dd"));
al.add(new Student(3,"cc"));
Collections.sort(al,new StudentComparator());
Iterator it=al.iterator();
while(it.hasNext()){
System.out.println(it.next());
}
}
}
class Student {
int id;
String name;
Student(int id,String name){
this.id=id;
this.name=name;
}
public String toString(){
return "id="+this.id+",name="+this.name;

}
}

class StudentComparator implements Comparator{
public int compare(Object o1,Object o2){
Student s1=(Student)o1;
Student s2=(Student)o2;
int result=(s1.id>s2.id)?1:((s1.id==s2.id)?0:-1);
if(0==result){
result=s1.name.compareTo(s2.name);

}
return result;
}
}