运行异常为什么啊
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(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:"+temp0.id+":"+temp0.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("添加了两门课程:"+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);
}
/**
* 通过 for each 方法访问集合元素
* @param args
*/
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);
}
}
/**
* @param args
*/
public static void main(String[] args) {
SetTest st=new SetTest();
st.testAdd();
st.testForEach();
//创建一个学生对象
Student student=new Student("1","小明");
System.out.println("欢迎学生"+student.name+"选课");
//创建一个Scannner对象,用来接收从键盘输入的课程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,学生所选的课程!
for(Course cr:student.courses){
System.out.println("选择了课程:"+cr.id+":"+cr.name);
}
}
}
运行结果
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 4, Size: 4
at java.util.ArrayList.rangeCheck(ArrayList.java:604)
at java.util.ArrayList.get(ArrayList.java:382)
at com.imooc.collection.SetTest.testAdd(SetTest.java:34)
at com.imooc.collection.SetTest.main(SetTest.java:62)