为何会越界异常
package com.imooc.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() {
/*
* 创建一个课程对象,并通过调用add方法,添加到备选课程List中
*/
Course cr1 = new Course("1","数据结构");
coursesToSelect.add(cr1);
Course temp = (Course) coursesToSelect.get(0);
// System.out.println("添加了课程:" + temp.id + temp.name);
Course cr2 = new Course("2","C语言");
coursesToSelect.add(0, cr2);
Course temp2 = (Course)coursesToSelect.get(1);
// System.out.println("添加了课程:" + temp2.id + ":" +temp2.name);
// coursesToSelect.add(cr1);
// Course temp0 = (Course) coursesToSelect.get(0);
// System.out.println("添加了课程:" + temp.id + temp.name);
//以下方法会抛出数组下标越界异常
// Course cr3 = new Course("3","test");
// coursesToSelect.add(4, cr3);
Course course[] = {new Course("3","离散数学"), new Course("4","汇编语言")};
coursesToSelect.addAll(Arrays.asList(course));
Course temp3 = (Course) coursesToSelect.get(3);
Course temp4 = (Course) coursesToSelect.get(4);
// System.out.println("添加了2门课程" + temp3.id + ":" +
// temp3.name + ";" + temp4.id + ":" + temp4.name);
Course course2[]= {new Course("5","高等数学"), new Course("6","大学英语")};
coursesToSelect.addAll(2, Arrays.asList(course2));
Course temp5 = (Course) coursesToSelect.get(2);
Course temp6 = (Course) coursesToSelect.get(3);
// System.out.println("添加了两门课程"+ temp5.id + ":" +temp5.name +
// temp6.id + ":" + temp6.name);
}
public void testForEach() {
System.out.println("有以下课程待选(通过for each返回):");
for(Object obj:coursesToSelect) {
Course cr = (Course) obj;
System.out.println("课程:" + cr.id + ":" + cr.name);
}
}
public static void main(String[] args) {
// TODO Auto-generated method stub
SetTest st = new SetTest();
st.testAdd();
st.testForEach();
//创建一个新的学生对象
Student student = new Student("1","小明");
System.out.println("欢迎学生:" + student.name + "选课");
//创建一个scanner对象,用来接收用键盘输入的课程ID
Scanner console = new Scanner(System.in);
for(int i = 0; i < 3; i++) {
System.out.println("请输入课程ID:");
String courseId = console.next();
for (Course cr : st.coursesToSelect) {
if(cr.id.equals(courseId)) {
student.courses.add(cr);
}
}
}
st.testForEachForSet(student);
}
public void testForEachForSet(Student student) {
//打印输出学生所选课程
for(Course cr : student.courses) {
System.out.println("选择了课程" + cr.id + cr.name);
}
}
}