static
<T extends Comparable <? super T>>
void
sort ( List <T>?list)
 Sorts the specified list into ascending order,
according to the natural ordering of its elements.
static
<T> void
sort ( List <T>?list, Comparator <? super T>?c)
 Sorts the specified list according to the order
?induced by the specified comparator.

API如上

具體使用方法:

第一種方法:容器內要排序的類必須時下Comparable接口,Comparable接口來自java.lang包
必須實現下面這個方法:
intcompareTo(T?o)
Compares this object with the specified object for order.

例子:
import java.util.*;
public class Main{
??? public static void main(String args[]){
??????? ArrayList<Student> al=new ArrayList<Student>();
??????? 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;
???????
??? }
}

第二種方法:使用靜態內部類實現Comparator接口,Comparator接口位于java.util包下
?intcompare(T?o1, T?o2)
Compares its two arguments for order.
?booleanequals(Object?obj)
Indicates whether some other object is "equal to" this Comparator.


只需實現compare方法就行,equals方法在obeject類就會有,而實體類繼承自object類,就必然會有equals方法,所以不需實現

例子
import java.util.*;
public class Main{
??? public static void main(String args[]){
??????? ArrayList<Student> al=new ArrayList<Student>();
??????? 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 Student.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;
???????
??? }
??? static 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;
??????? }
??? }
}