1、一个类在设计之初就要实现对该类对象的排序功能，那么这个类要实现Comparable接口，实现public int compareTo(T t)方法。如代码中的Student类。
对于实现Comparable接口的类，
调用java.util.Arrays.sort(Object[] a)对包含对象实例的数组进行排序，
调用java.util.Collections.sort(List<T> list)对包含对象实例的list进行排序。
2、若一个类在设计之初并没有对排序功能的需求，而是在后续的使用中想要对这个类添加排序的功能，如Teacher类。这时的办法是实现一个比较器类，
如TeacherComparator类，实现public int compare(T t1, T t2)让该类实现Comparator接口。
调用java.util.Arrays.sort(T[] a, Comparator<? super T> c) 对包含对象实例的数组进行排序，
调用java.util.Collections.sort(List<T> list, Comparator<? super T> c) 对包含对象实例的list进行排序。
3、a.compareTo(b)方法和compare(a,b)方法，在方法中判断两个对象的某个或某些属性的大小关系，若a的某个属性比b的属性小，返回负整数，若相等，返回0，否则返回正整数。
if a.attr < b.attr
return -1
else
return 1
上面即为按照某属性从小到大排序。
if a.attr < b.attr
return 1
else
return -1
上面为按照某属性从大到小排序。
以下代码按照Score从高到底排序，若Score相同，则按照age从小到大排序。
public class Student implements Comparable<Student>{
private String name;
private int id;
private int score;
private int age;
public Student(String name, int id, int score, int age) {
super();
this.name = name;
this.id = id;
this.score = score;
this.age = age;
}
@Override
public int compareTo(Student s) {
if (this.score < s.getScore()) {
return 1;
} else if (this.score > s.getScore()) {
return -1;
} else {
if (this.age < s.getAge()) {
return -1;
} else {
return 1;
}
}
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public static void main(String[] args) {
System.out.println("use Interface Comparable");
System.out.println();
System.out.println("Array ");
System.out.println();
Student[] stu = {new Student("a", 1, 88, 18),
new Student("b", 2, 78, 16),
new Student("c", 3, 88, 17),
new Student("d", 4, 78, 16),
new Student("e", 5, 100, 18)};
Arrays.sort(stu);
for (Student s : stu) {
System.out.println(s.getScore() + " " + s.getAge());
}
System.out.println("***");
System.out.println("List");
System.out.println();
List<Student> list = new ArrayList<Student>();
list.add(new Student("a", 1, 88, 18));
list.add(new Student("b", 2, 78, 16));
list.add(new Student("c", 3, 88, 17));
list.add(new Student("d", 4, 78, 16));
list.add(new Student("e", 5, 100, 18));
Collections.sort(list);
for (Student s : list) {
System.out.println(s.getScore() + " " + s.getAge());
}
System.out.println();
System.out.println("use Interface Comparator");
System.out.println();
System.out.println("Array");
System.out.println();
Teacher[] teach = {
new Teacher("a", 1, 88, 18),
new Teacher("b", 2, 78, 16),
new Teacher("c", 3, 88, 17),
new Teacher("d", 4, 78, 16),
new Teacher("e", 5, 100, 18)};
Arrays.sort(teach, new TeacherComparator());
for (Teacher t : teach) {
System.out.println(t.getScore() + " " + t.getAge());
}
System.out.println();
System.out.println("List");
System.out.println();
List<Teacher> tList = new ArrayList<Teacher>();
tList.add(new Teacher("a", 1, 88, 18));
tList.add(new Teacher("b", 2, 78, 16));
tList.add(new Teacher("c", 3, 88, 17));
tList.add(new Teacher("d", 4, 78, 16));
tList.add(new Teacher("e", 5, 100, 18));
Collections.sort(tList, new TeacherComparator());
for (Teacher t : tList) {
System.out.println(t.getScore() + " " + t.getAge());
}
}
}
class Teacher {
private String name;
private int id;
private int score;
private int age;
public Teacher(String name, int id, int score, int age) {
super();
this.name = name;
this.id = id;
this.score = score;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
class TeacherComparator implements Comparator<Teacher> {
@Override
public int compare(Teacher t1, Teacher t2) {
if (t1.getScore() < t2.getScore()) {
return 1;
} else if (t1.getScore() > t2.getScore()) {
return -1;
} else {
if (t1.getAge() < t2.getAge()) {
return -1;
} else {
return 1;
}
}
}
}