1.定義一個Student類，包括學號，姓名，成績三個字段，生成get,set和toString方法,實現Comparable接口，重寫toCompare方法，方法里就是本題的邏輯，先按成績比較，再按學好比較，使用TreeSet不實現這個接口會報錯。

package Collection;

public class Student implements Comparable<Student> {
private long sno;
private String name;
private int score;

public long getSno() {
return sno;
}

public void setSno(long sno) {
this.sno = sno;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getScore() {
return score;
}

public void setScore(int score) {
this.score = score;
}

@Override
public int compareTo(Student o) {
// TODO Auto-generated method stub
if (this.score < o.score) {
return 1;
} else if (this.score > o.score) {
return -1;
} else {
if(this.sno<o.sno) {
return 1;
}else {
return -1;
}

}
}
@Override
public String toString() {
return "Student [sno=" + sno + ", name=" + name + ", score=" + score + "]";
}
}

2.然后寫測試類，生成十個學生，然后插入treeset，直接遍歷輸出就是排序好的結果。

package Collection;

import java.util.Random;
import java.util.TreeSet;

public class TreeSetTest {
public static void main(String[] args) {
TreeSet<Student> ts=new TreeSet<Student>();
for(int i=0;i<10;i++) {
Student stu=new Student();
stu.setName("student"+i);
stu.setSno(170201+i);
stu.setScore(90+new Random().nextInt(10));
ts.add(stu);
}

for(Student stu:ts) {
System.out.println(stu);
}
}
}

最后貼一個運行結果

實現如下：

public static void main(String[] args) {
    //使用TreeSet集合自帶排序，排序規則由Comparator中的compare方法確定
    TreeSet<Student> set = new TreeSet<>(new Comparator<Student>() {
        @Override
        public int compare(Student o1, Student o2) {
            if (o1.getScore() == o2.getScore()){
                //分數一樣，學號小的在前
                return o1.getStudentNo() - o2.getStudentNo();
            }
            //分數不一樣，分數大的在前
            return o2.getScore() - o1.getScore();
        }
    });
    Student s1 = new Student(170201, "s1", 78);
    Student s2 = new Student(170203, "s1", 58);
    Student s3 = new Student(170202, "s1", 78);
     set.add(s1);
     set.add(s2);
     set.add(s3);
     System.out.println(set);
}

//學生類
class Student{
    private int studentNo;
    private String name;
    private int score;

    public Student(int studentNo, String name, int score) {
        this.studentNo = studentNo;
        this.name = name;
        this.score = score;
    }

    public int getScore(){
        return score;
    }

    public int getStudentNo() {
        return studentNo;
    }

    @Override
    public String toString() {
        return "姓名：" + name + ",學號：" + studentNo + ",分數：" + score;
    }
}

public class main
{
public static void main(String[] args)
{
Person p = new Person("Parker","Male",17);
Teacher t = new Teacher("John","Male",46,"Professor","Maths");
Student s = new Student("Mary","Female",18,"12345","2010/9/1","Physics");
System.out.println(p);
System.out.println(t);
System.out.println(s);
}
}
class Person
{
public Person(String n, String s, int a)
{
name = n;
sex = s;
age = a;
}
public String toString()
{
String temp;
temp = "name: ".concat(name);
temp = temp.concat(", sex: ".concat(sex));
temp = temp.concat(", age: ".concat(Integer.toString(age)));
return temp;
}
public String name;
public String sex;
public int age;
}

class Teacher extends Person
{
public Teacher(String n, String s, int a, String p, String d)
{
super(n,s,a);
position = p;
department = d;
}
public String position;
public String department;
public String toString()
{
String temp = super.toString();
temp = temp.concat(", position: ".concat(position));
temp = temp.concat(", department: ".concat(department));
return temp;
}
}

class Student extends Person
{
public Student(String n, String s, int a, String i, String e, String m)
{
super(n,s,a);
id = i;
entranceDate = e;
major = m;
}
public String toString()
{
String temp = super.toString();
temp = temp.concat(", id: ".concat(id));
temp = temp.concat(", entranceDate: ".concat(entranceDate));
temp = temp.concat(", major: ".concat(major));
return temp;
}
public String id;
public String entranceDate;
public String major;
}

第一題：
public class C {

public int x = 100;

public void disp(){
System.out.println(x);
}

public static void main(String args[]){
new C().disp();
new D().dispC();
new D().dispD();
}
}

class D extends C{
private int x = 99;

public void dispD(){
System.out.println(this.x);
}

public void dispC(){
System.out.println(super.x);
}
}

第二題：
接口：
public interface Draw {

/**
* 計算周長
* side 邊長
*/
public void calGirth(int side);

/**
* 計算面積
* side 邊長
*/
public void calSize(int side);
}
實現：
public class DrawImpl implements Draw{

public void calGirth(int side) {
System.out.println("周長為：" + 4*side);
}

public void calSize(int side) {
System.out.println("面積為：" + side*side);
}

public static void main(String args[]){
new DrawImpl().calGirth(5);
new DrawImpl().calSize(5);
}

}

你好，我的第3題代碼出來了，可以直接運行

public class Test1 {
public static void main(String[] args) {
M3 m = new M3();
m.pa();
m.pb();

M3 m3 = new M3(3);
m3.pa();
}
}

class M3 {
int n = 5;
int m = 10;

public M3() {
n = 100;
m = 200;
}

public M3(int n) {
this.n = n;
}

public void pa() {
for (int i = 0; i < n; i++) {
System.out.print("*");
}
System.out.println();
}

public void pb() {
for (int i = 0; i < m; i++) {
System.out.print("*");
}
System.out.println();
}
}

運行結果：

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oh my god!