import java.util.*;  
//以下是學生類Student定義，有點類似C語言的結構體啊！^_^  
class Student {  
    public int s_no;  
    public String s_name;  
    public int s_class;  
}  
  
public class compareTest {  
    public static void main(String[] args) {  
        //存放學生類的動態陣列的初始化  
        ArrayList<Student> studentArr = new ArrayList<Student>();  
        Student s1 = new Student();  
        s1.s_no = 3;  
        s1.s_name = "a";  
        s1.s_class = 102;  
        studentArr.add(s1);  
        Student s2 = new Student();  
        s2.s_no = 2;  
        s2.s_name = "b";  
        s2.s_class = 101;  
        studentArr.add(s2);  
        Student s3 = new Student();  
        s3.s_no = 1;  
        s3.s_name = "c";  
        s3.s_class = 103;  
        studentArr.add(s3);  
        //初始化之後先列印以下這個動態陣列  
        System.out.println("排序前：");  
        for (int i = 0; i < studentArr.size(); i++) {  
            System.out  
                    .println("我是" + studentArr.get(i).s_class + "班的"  
                            + studentArr.get(i).s_name + "學號是"  
                            + studentArr.get(i).s_no);  
        }  
        //對於Comparator介面的重寫  
        //這個介面就一個抽象函式，給出的引數與返回值都是定死的。  
        Collections.sort(studentArr, new Comparator<Object>() {  
            public int compare(Object o1, Object o2) {  
                //你首先設定你要比較的東西  
                //具體是把引數中的Object強制轉換成你要比較的東西，這裡是兩個Student類  
                //這裡的s1,s2與上面的s1,s2一點關係都沒有，只是抽象的前者與後者的關係  
                Student s1 = (Student) o1;  
                Student s2 = (Student) o2;  
                //如果前者的學號大於後者的學號，就是前者大於後者，返回1系統就會識別是前者大於後者  
                if (s1.s_no > s2.s_no) {  
                    return 1;  
                }  
                //小於同理  
                if (s1.s_no < s2.s_no) {  
                    return -1;  
                }  
                //如果返回0則認為前者與後者相等  
                return 0;  
            }  
        });  
        //比較完畢再輸出以學號排序之後的結果  
        System.out.println("按學號排序後：");  
        for (int i = 0; i < studentArr.size(); i++) {  
            System.out  
                    .println("我是" + studentArr.get(i).s_class + "班的"  
                            + studentArr.get(i).s_name + "學號是"  
                            + studentArr.get(i).s_no);  
        }  
        //以下是以班級排序的過程  
        Collections.sort(studentArr, new Comparator<Object>() {  
            public int compare(Object o1, Object o2) {  
                Student s1 = (Student) o1;  
                Student s2 = (Student) o2;  
                if (s1.s_class > s2.s_class) {  
                    return 1;  
                }  
                if (s1.s_class < s2.s_class) {  
                    return -1;  
                }  
                return 0;  
            }  
        });  
        System.out.println("按班級排序後：");  
        for (int i = 0; i < studentArr.size(); i++) {  
            System.out  
                    .println("我是" + studentArr.get(i).s_class + "班的"  
                            + studentArr.get(i).s_name + "學號是"  
                            + studentArr.get(i).s_no);  
        }  
    }  
}