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 class ListTest{ ?/* ? ?用于存放備選課程的List ?*/ ?public List coursesToSelect; ?public ListTest(){ ? ?this.coursesToSelect=new ArrayList(); ?} ?/* ?用于往coursesToSelect中添加備選課程 ?*/ ?public void testAdd(){ ? ?//創(chuàng)建一個課程對象，并通過調(diào)用add方法，添加到備選課程List中 ? ?Course cr1=new Course("1","數(shù)據(jù)結(jié)構(gòu)"); ? ?coursesToSelect.add(cr1); ? ?Course temp=(Course)coursesToSelect.get(0); ? ?//System.out.println("添加了課程:"+temp.id+":"+temp.name); ? ?Course cr2=new Course("2","c語言"); ? ?coursesToSelect.add(0,cr2); ? ?Course temp2=(Course)coursesToSelect.get(0); ? ?//System.out.println("添加了課程:"+temp2.id+":"+temp2.name); ? ? ? ?//coursesToSelect.add(cr1); ? ?//Course temp0=(Course)coursesToSelect.get(2); ? ?//System.out.println("添加了課程:"+temp0.id+":"+temp0.name); ? ?Course[] course={new Course("3","離散數(shù)學"),new Course("4","匯編語文" )}; ? ?coursesToSelect.addAll(Arrays.asList(course)); ? ?Course temp3=(Course)coursesToSelect.get(3); ? ?Course temp4=(Course)coursesToSelect.get(4); ? ?//System.out.println("添加了兩門課程:"+temp3.id+":"+temp3.name+";"+temp4.id+":"+temp4.name); ? ? ? ?Course[] course2={new Course("5","高等數(shù)學"),new Course("6","大學英語")}; ? ?coursesToSelect.addAll(2,Arrays.asList(course)); ? ?Course temp5=(Course)coursesToSelect.get(2); ? ?Course temp6=(Course)coursesToSelect.get(3); ? ?//System.out.println("添加了兩門課程:"+temp5.id+":"+temp5.name+";"+temp6.id+":"+temp6.name); ?} ?} ? ?/* ?通過for each方法訪問集合元素 ?*/ ?public void testForEach(){ ? ?System.out.println("有如下課程待選(通過for each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){ ? ?SetTest st=new SetTest(); ? ?st.testAdd(); ? ?st.testForEach();? ? ?//創(chuàng)建一個學生對象 ? ?Student student=new Student("1","小明"); ? ?System.out.println("歡迎學生："+student.name+"選課！"); ? ?//創(chuàng)建一個Scanner對象，用來接收從鍵盤輸入的課程ID ? ?Scanner console=new Scanner(System.in); ? ?for(int i=0;i<3;i++){ ? ? ?System.out.println("請輸入課程ID"); ? ? ?String courseId=console.next(); ? ? ?for(Course cr:st.coursesToSelect){ ? ? ? ?if(cr.id.equals(courseId)){ ? ? ? ? ?student.courses.add(cr); ? ? ? ?} ? ? ?} ? ?} ? st.testForEachForSet(student); ?} ? ? ?private void testAdd() { // TODO Auto-generated method stub } public void testForEachForSet(Student student){ ? ?//打印輸出，學生所選的課程 System.out.println("共選擇了："+student.courses.size()+"門課程"); ? ?for(Course cr:student.courses){ ? ? ?System.out.println("選擇了課程："+cr.id+":"+cr.name); ? ?} ?} }??這是我的代碼，運行完后是這個樣子的，不知道什么情況有如下課程待選(通過for each訪問)：歡迎學生：小明選課！請輸入課程ID4請輸入課程ID1請輸入課程ID4共選擇了：0門課程