為什么我每次輸入2 1 4，輸出的結果都是1 2 4，不會出現其他的順序

//學生類中定義的Set集合
public?class?Student?{
????public?String?ip;
????public?String?name;
????public?Set<Course>?courses;//Set類型?存放選課信息
????public?Student(String?ip,String?name){
????	this.ip?=?ip;
????	this.name?=?name;
????	this.courses?=?new?HashSet<Course>();//初始化courses
????}
}
//遍歷輸出Set集合中的元素
public?void?setForEach(Student?student){
		System.out.println("共選擇了"+student.courses.size()+"門課程:");
		for(Course?set1:student.courses){
			System.out.println("課程："+set1.id+":"+set1.name);
		}
		
	}