一道Java集合框架题 多种解题思路

import java.util.ArrayList; 
import java.util.Collections; 
import java.util.Comparator; 
import java.util.Iterator; 
import java.util.LinkedList; 
import java.util.TreeMap; 
public class Test2{ 
  public static void main(String[] args){ 
    /* 此处用ArrayList实现 
     * 
     * ArrayList<Student>al=new ArrayList<Student>(); 
    for(int i=20070301,j=10;i<=20070330;i++,j++) 
    { 
      al.add(new Student(i,(int) (40*Math.random()+60), "同学"+j)); 
    } 
    //ArrayList排序借助Collections中的sort()方法实现。 
    Collections.sort(al, new Sortbygrade()); 
    for(Student sd:al) 
    System.out.println(sd); 
    */ 
    LinkedList<Student> lt=new LinkedList<Student>(); 
    for(int i=20070301,j=10;i<=20070330;i++,j++) 
    { 
      lt.add(new Student(i,(int) (40*Math.random()+60), "同学"+j)); 
    } 
    //对链表排序 
    Collections.sort(lt, new Sortbygrade()); 
    //输出链表 
    for(Student sd:lt) 
      System.out.println(sd); 
  } 
} 
//学生类 
class Student{ 
  int num,grade; 
  String name; 
  //构造函数 
  public Student(int num,int grade,String name){ 
    this.num=num; 
    this.name=name; 
    this.grade=grade; 
  } 
  //此处必须覆写 
  public String toString(){ 
//   System.out.println("hi"); 
    return "学号："+this.num+"\t"+"姓名:"+this.name+"  "+"成绩:"+this.grade; 
  } 
} 
//创建一个比较器类 
class Sortbygrade implements Comparator<Student>{ 
  @Override 
  public int compare(Student s1, Student s2) { 
    if(s1.grade>s2.grade) 
      return 1; 
    if(s1.grade<s2.grade) 
      return -1; 
    if(s1.grade==s2.grade) 
      return s1.name.compareTo(s2.name); 
    return 0;     
  } 
} 

for(int i=0;i<lt.size();i++) 
{ 
  Student s=lt.get(i); 
  System.out.println("学号："+s.num+"  姓名："+s.name+"  成绩："+s.grade); 
} 

package com.package1; 
import java.util.*; 
public class StuScore { 
public static void main(String[] args) { 
  TreeSet<Student> ts=new TreeSet<Student>(new Com()); 
  //添加元素进去 
  for(int i=20070301,j=1;i<=20070330;i++,j++) 
  { 
    ts.add(new Student(i,"同学"+j,(int) (40*Math.random()+60))); 
  } 
  //迭代循环取出 
  Iterator<Student> it=ts.iterator(); 
  while(it.hasNext()) 
  { 
    Student o1=it.next(); 
    System.out.println("学号："+o1.num+" "+"姓名："+o1.name+" "+" "+"成绩："+o1.grade); 
  } 
} 
} 
//学生类 
class Student  
{ 
int num; 
int grade; 
String name; 
public Student(int num, String name,int grade) 
{ 
  this.num=num; 
  this.name=name; 
  this.grade=grade; 
} 
} 
class Com implements Comparator 
{ 
@Override 
public int compare(Object o1, Object o2) { 
  Student s1=(Student) o1; 
  Student s2=(Student) o2; 
  if(s1.grade>s2.grade) 
    return 1; 
  if(s1.grade<s2.grade) 
    return -1; 
  if(s1.grade==s2.grade) 
  { 
    return new Integer(s1.num).compareTo(new Integer(s2.num)); 
  } 
  return 0; 
} 
} 

package com.package1; 
import java.util.*; 
public class StuScore { 
  public static void main(String[] args) { 
    HashSet<Student> hs=new HashSet<Student>(); 
    //添加元素进去 
    for(int i=20070301,j=1;i<=20070330;i++,j++) 
    { 
      hs.add(new Student(i,"同学"+j,(int)  
(40*Math.random()+60))); 
    } 
    ArrayList<Student>li=new ArrayList(hs); 
    Collections.sort(li, new Sortbygrade()); 
    for(Student ss:li) 
      System.out.println(ss); 
  } 
} 
//学生类 
class Student  
{ 
  int num; 
  int grade; 
  String name; 
  public Student(int num, String name, int grade) 
  { 
    this.num=num; 
    this.name=name; 
    this.grade=grade; 
  } 
  public String toString(){ 
    //System.out.println("hi"); 
    return "学号："+this.num+"\t"+"姓名:"+this.name 
+"  "+"成绩:"+this.grade; 
  } 
} 
class Sortbygrade implements Comparator{ 
  @Override 
  public int compare(Object o1, Object o2) { 
    Student s1=(Student) o1; 
    Student s2=(Student) o2; 
    if(s1.grade>s2.grade) 
      return 1; 
    if(s1.grade<s2.grade) 
      return -1; 
//   if(s1.grade==s2.grade) 
    return 0; 
  } 
} 

package com.package1;  
import java.util.Comparator; 
import java.util.Iterator; 
import java.util.Set; 
import java.util.TreeMap; 
public class TestTreeMap { 
  public static void main(String[] args) { 
    //1.创建集合 
    TreeMap<Student,Integer> tm=new TreeMap<Student,Integer>(); 
    for(int i=20070301,j=10;i<=20070330;i++,j++) 
    { 
      int grade=(int) (40*Math.random()+60); 
       //2、往集合对象中添加元素 
       tm.put(new Student(grade,"同学"+j),i); 
    } 
    //3.遍历集合 ，排序完成  
    Set<Student> k=tm.keySet(); 
    Iterator<Student> it=k.iterator(); 
    while(it.hasNext()){ 
      Student key=it.next(); 
      Integer num=tm.get(key); 
      System.out.println("学号："+num+"  "+"姓名："+key.name+"  "+"成绩:"+key.grade); 
    } 
  } 
} 
class Student implements Comparable<Student>{ 
  int grade; 
  String name; 
  public Student(int grade,String name){ 
    this.grade =grade; 
    this.name=name; 
  } 
  @Override 
  public int compareTo(Student o) { 
    if(this.grade>o.grade)  
      return 1;  
      if(this.grade==o.grade)  
      { //当成绩相同时，按照姓名排序 
       return this.name.compareTo(o.name);  
      }  
      return -1;  
  } 
}