有个小问题希望得到帮助

Question

package collection_map;import java.util.ArrayList;import java.util.Arrays;import java.util.Iterator;import java.util.List;public class TestNow { public List coursesToSelect; public TestNow(){ this.coursesToSelect=new ArrayList(); } public void testAdd(){ Course cr1=new Course("1","数据结构"); coursesToSelect.add(cr1); Course temp=(Course)coursesToSelect.get(0);//0是因为，List与数组一样，起始位置也是0 //又因为对象存入集合都会变成object类型，取出时需要类型转换，这里的(Course)就是强制类型转换 System.out.println("添加了课程:"+temp.id+":"+temp.name); Course cr2=new Course("2","JAVA基础"); coursesToSelect.add(1,cr2); Course temp2=(Course)coursesToSelect.get(0); System.out.println("在后边添加了课程:"+cr2.id+":"+cr2.name); Course cr3[]={new Course("3","线性代数"),new Course("4","高中化学")}; coursesToSelect.addAll(2,Arrays.asList(cr3)); Course temp3=(Course)coursesToSelect.get(2); Course temp4=(Course)coursesToSelect.get(3); System.out.println("用数组添加了两门课程："+temp3.id+":"+temp3.name+"以及" +temp4.id+":"+temp4.name ); } public void testGet(){ int size=coursesToSelect.size(); for(int i=0;i<size;i++) { Course tempt=(Course)coursesToSelect.get(i); System.out.println(tempt.id+":"+tempt.name); } } public void testIterator(){ Iterator ir=coursesToSelect.iterator(); System.out.println("通过迭代器访问："); while(ir.hasNext()) { Course cs=(Course)ir.next(); System.out.println(cs.id+":"+cs.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 cs=(Course) obj; System.out.println("课程："+cs.id+":"+cs.name); } } public void testModify(){ coursesToSelect.set(0, new Course("1","被换啦哈哈哈"));//就是这里 } public static void main(String[] args) { TestNow tn=new TestNow(); tn.testAdd(); tn.testGet(); tn.testIterator(); tn.testForEach(); tn.testModify(); }在标注的地方那行代码不知道为什么起作用，1还是数据结构}

Answer 1

你最好还是把这些代码在袁问中用java代码语言打印出来