已采纳回答 / ziom
要把 Math.random()*10用圆括号裹起来，不然会先将Math.random()生成的小于1的随机数转换成int再与10相乘，所以你这样写的话 (int) Math.random()的结果必然是0，在乘以10，结果也自然会是0求采纳！
2017-02-20
右键--》Source -->Generate hashcode() and equals(),弹出框中选中name，确定。
2017-02-20
SetStudent ss = new SetStudent();
ss.testAdd();
ss.testForeach();
Student student = new Student();
student.id="1";
student.name="小名";
System.out.println("请学生："+student.name+"同学选课");
ss.testAdd();
ss.testForeach();
Student student = new Student();
student.id="1";
student.name="小名";
System.out.println("请学生："+student.name+"同学选课");
2017-02-18
Scanner sc = new Scanner(System.in);
for(int i = 0;i < 3; i++){
System.out.println("请输入课程ID");
String courseId = sc.next();
for (Course cr : ss.courseToSelect) {
if(cr.id.equals(courseId)){
student.course.add(cr);
}
}
}
ss.testForeach();
for(int i = 0;i < 3; i++){
System.out.println("请输入课程ID");
String courseId = sc.next();
for (Course cr : ss.courseToSelect) {
if(cr.id.equals(courseId)){
student.course.add(cr);
}
}
}
ss.testForeach();
2017-02-18
Exception in thread "main" java.lang.NullPointerException
at com.imooc_collection_one.SetStudent.main(SetStudent.java:58)
空指针是为什么！
at com.imooc_collection_one.SetStudent.main(SetStudent.java:58)
空指针是为什么！
2017-02-18
