為什么我的程序會出現異常
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() {
//創建一個課程對象,并通過調用add方法,添加到備選課程List中
Course cr1=new Course("1","數據結構 ");
coursesToSelect.add(cr1);
Course temp=(Course) coursesToSelect.get(0);
//System.out.println("添加了一個課程:"+temp.id+":"+temp.name);
Course cr2=new Course("2","C語音");
coursesToSelect.add(0, cr2);
Course temp2=(Course)coursesToSelect.get(0);
//System.out.println("添加了一個課程:"+temp2.id+":"+temp2.name);
/*courseToSelect.add(cr1);
Course temp0=(Course) courseToSelect.get(2);
System.out.println("添加了一個課程:"+temp.id+":"+temp.name);*/
//以下方法會拋出數組下標越界異常
//Course cr3=new Course("3","xxx");
//courseToselect.add(4, cr3);
Course[] course= {new Course("3","離散數學"),new Course("4","匯編語音")};
coursesToSelect.addAll(Arrays.asList(course));
Course temp3=(Course)coursesToSelect.get(3);
coursesToSelect.get(4);
Course[] course2= {new Course("5","高等數學"),new Course("6","大學英語")};
coursesToSelect.addAll(2,Arrays.asList(course2));
Course temp5=(Course)coursesToSelect.get(2);
Course temp6=(Course)coursesToSelect.get(3);
//System.out.println("添加了倆個課程:"+temp5.id+":"+temp5.name+";"+temp6.id+":"+temp6.name);
}
/**
* 通過for each 方法訪問集合元素
* @param args
*/
public void testForEach(){
System.out.println("有如下課程可選(通過for each方法訪問):");
for(Object obj:coursesToSelect) {
Course cr=(Course) obj;
System.out.println("課程:"+cr.id+":"+cr.name);
}
}
public static void main(String[] args) {
// TODO Auto-generated method stub
SetTest st=new SetTest();
st.testAdd();
st.testForEach();
//創建一個新的學生對象
Student student=new Student("1","小明");
System.out.println("歡迎學生:"+student.name+"選課!");
//創建一個Scanner對象,用來接收從鍵盤輸入的課程ID
@SuppressWarnings("resource")
Scanner console=new Scanner(System.in);
for(int i=0;i<3;i++) {
System.out.println("輸入課程ID");
String courseId=console.next();
for(Course cr:st.coursesToSelect) {
if(cr.id.equals(courseId)) {
student.courses.add(cr);
student.courses.add(cr);
}
}
}
st.testForEachForSet(student);
}
? ? public void testForEachForSet(Student student) {
? ? //打印輸出 學生所選的課程
? ? for(Course cr:student.courses) {
? ? System.out.println("您選擇了課程:"+cr.id+":"+cr.name);
? ? }
? ? }
}
? ??
2019-02-03
問題:數組下標越界
應該改成