Exception in thread "main" java.lang.IndexOutOfBoundsException: Index 4 out-of-bounds for length 4	
at java.base/jdk.internal.util.Preconditions.outOfBounds(Unknown Source)	
at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Unknown Source)	
at java.base/jdk.internal.util.Preconditions.checkIndex(Unknown Source)	
at java.base/java.util.Objects.checkIndex(Unknown Source)	
at java.base/java.util.ArrayList.get(Unknown Source)	
at imooc_collection_map_demo/com.imooc.collection.SetTest.testAdd(SetTest.java:34)	
at imooc_collection_map_demo/com.imooc.collection.SetTest.main(SetTest.java:58)

//源代码在下面

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() {

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(0);

//System.out.println("添加了课程："+temp2 .id+":"+temp2.name);

//coursesToSelect.add(cr1);

//Course temp0 = (Course) coursesToSelect.get(2);

//System.out.println("添加了课程："+temp.id+":"+temp.name);

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("添加了课程："+temp3.id+":"+temp3.name);

//System.out.println("添加了课程："+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("有如下课程待选(通过for each访问)：");

for(Object obj :  coursesToSelect) {

Course cr = (Course) obj;

System.out.println("课程：" + cr.id + ":" + cr.name);

}

}

public static void main(String[] args) {

// TODO 自动生成的方法存根

SetTest st = new SetTest();

st.testAdd();

st.testForEach();

Student student = new Student("1","小明");

System.out.println("欢迎学生：" + student.name + "选课！");

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) {

for(Course cr : student.courses) {

System.out.println("选择了课程：" + cr.id + ":" + cr.name);

}

}

}