Java—集合框架Set

package com.test.collection;

/**
 * 课程类
 * @author Administrator
 *
 */
public class Course {
    public String id;
    public String name;
    public Course(String id, String name){
        this.id = id;
        this.name = name;
    }
}

package com.test.collection;

import java.util.HashSet;
import java.util.Set;
/**
 * 学生类
 * @author Administrator
 *
 */
public class Student {
    public String id;
    public String name;
    public Set<Course> courses;//所选课程
    public Student(String id, String name) {
        this.id = id;
        this.name = name;
        this.courses = new HashSet<Course>();//实例化sourses接口（Set是接口，接口不能被直接实例化）
    }
}

package com.test.collection;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class SetTest {
    public List<Course> coursesToSelect;
    public SetTest() {
        coursesToSelect = new ArrayList<Course>();
    }
    public void testAdd() {
        Course c1 = new Course("1", "数据结构");//创建课程对象的实例
        Course c2 = new Course("2", "C语言");
        Course c3 = new Course("3", "离散数学");
        Course c4 = new Course("4", "汇编语言");
        Course[] course = {c1, c2, c3, c4};
        coursesToSelect.addAll(Arrays.asList(course));
    }
    
    public void testForEach() {
        System.out.println("有以下课程可以选择：(通过For Each)");
        for (Object obj : coursesToSelect) {
            Course c = (Course) obj;
            System.out.println("课程：" + c.id + ":" + c.name);
        }
    }
    
    public void testForEachForSet(Student student) {
        System.out.println("共选择了" + student.courses.size() + "门课程！");
        for (Course c : student.courses) {
            System.out.println("选择了课程：" + c.id + ":" + c.name);
        }
    }
    
    public static void main(String[] args) {
        SetTest st = new SetTest();
        st.testAdd();
        st.testForEach();
        
        Student student = new Student("1", "李雷");
        Scanner console = new Scanner(System.in);
        
        for (int i = 0; i < 3; i++) {
            System.out.println("请输入课程编号：");
            String courseId = console.next();
            for(Course c : st.coursesToSelect ) {
                if (c.id.equals(courseId)) {
                    student.courses.add(c);
                    //student.courses.add(null);
                }
            }
        }
        
        st.testForEachForSet(student);
    }
}

有以下课程可以选择：(通过For Each)
课程：1:数据结构
课程：2:C语言
课程：3:离散数学
课程：4:汇编语言
请输入课程编号：
1
请输入课程编号：
3
请输入课程编号：
4
共选择了3门课程！
选择了课程：3:离散数学
选择了课程：1:数据结构
选择了课程：4:汇编语言