java集合问题

Question

Student类代码如下：import java.util.Arrays;import java.util.HashSet;import java.util.Set;public class Student { private String id; private String name; public Set<Course> courses; public Student(String id,String name){ this.id=id; this.name=name; this.courses = new HashSet<Course>();  //等价于HashSet courses = new HashSet();  } public Student(){ this.courses = new HashSet<Course>(); } public String getId() { return id; } public void setId(String id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; }}Test类代码import java.util.Arrays;import java.util.Iterator;public class Test { public void TestAdd2() { Student stu = new Student(); Course[] course = { new Course("1", "大学数学"), new Course("2", "大学英语"), new Course("3", "大学语文"), new Course("4", "汇编语言") , new Course("5", "大学数学"), new Course("6", "大学英语"), new Course("7", "大学语文"), new Course("8", "汇编语言")}; stu.courses.addAll(Arrays.asList(course)); System.out.println(stu.courses.size()); } public void TestForEach2() { Student stu = new Student(); for (Course c : stu.courses) { System.out.println("课程：" + c.getId() + ":" + c.getName()); } } public void testIterator(){ Student stu = new Student(); Iterator it = stu.courses.iterator(); System.out.println("有待选课程如下：(通过迭代器访问)"); while(it.hasNext()){ Course c = (Course)it.next(); System.out.println(c.getId()+":"+c.getName()); } } public void testRemove(){ Student stu = new Student(); Course[] course={new Course("1", "大学数学"), new Course("2", "大学英语")}; stu.courses.removeAll(Arrays.asList(course)); System.out.println("成功删除！"); } public static void main(String[] args) { TestSet ts = new TestSet(); ts.TestAdd2(); ts.TestForEach2(); ts.testIterator(); ts.testRemove(); }}为什么Student中的courses集合没有成功的添加数据，得出courses集合长度是1，为什么???????输出结果为：1有待选课程如下：(通过迭代器访问)成功删除！

Answer 1

你把Student stu = new Student();定义为Test类的成员变量

不然你每个方法中创建一个Student对象 ,操作的是不同的Student对象啊