[英]How Do I Iterate Generic List Using For Each Type For Loop
I have been given an assignment to create a list of lists where I should be able to iterate through the lists using the 'for each' type of 'for' loop, versus building a constructor for Iterator. 我已经获得了一个创建列表的列表,我可以使用'for each'类型的'for'循环遍历列表,而不是为Iterator构建一个构造函数。 The problem is that when I the code below, I get the error msg "Can only iterate over an array or an instance of java.lang.Iterable". 问题是当我下面的代码时,我得到错误消息“只能迭代数组或java.lang.Iterable的实例”。 Here is the code: 这是代码:
public static void main(String[] args) {
GList<InnerList> list = new GList<InnerList>();
GList<InnerList> numList = new GList<InnerList>();
InnerList lst = new InnerList ();
Scanner sc = new Scanner(System.in);
String answer;
while (true){
System.out.println ("Do you want to create a list (y/n)? ");
answer = sc.next();
if (answer.equals("y")){
System.out.println("Enter the name of the list: ");
answer = sc.next();
lst.setName(answer);
if (list.isEmpty()== true){
list.insertFirstItem(lst);
}
else {
list.insertNext(lst);
}
}
while (true){
System.out.println("Do you want to enter a number (y/n)?");
answer = sc.next();
if (answer.equals("y")){
System.out.println("Enter Number: ");
answer = sc.next();
try {
int num1 = Integer.parseInt(answer);
lst.setInner(num1);
if (list.isEmpty() == true){
list.insertFirstItem(lst);
}
else {
list.insertNext(lst);
}
}
catch (NumberFormatException e){
System.out.println("You must enter an number! " + e);
sc.close();
}
}
return;
}
}
for (GList<InnerList> ilName : list){ //here are my error msgs. I also tried replacing GList<InnerList> with 'InnerList' and String.
for(GList<InnerList> ilInts : list){
System.out.println(ilName);
System.out.println(ilInts);
}
}
}
Can someone help me understand why GList is not considered an instance of java.lang.iterable when collections should be iterable? 有人可以帮我理解为什么集合应该可迭代时,为什么GList不被视为java.lang.iterable的实例吗?
Thank you. 谢谢。
It's not considered as an instance of java.lang.Iterable
because it does not implement the interface java.lang.Iterable
. 它不被视为java.lang.Iterable
的实例,因为它没有实现接口java.lang.Iterable
。 As simple as that. 就如此容易。 Change its declaration to 将其声明更改为
public class GList<T> implements Iterable<T>
and you'll be ale to use the foreach loop with it. 你会很乐意使用它的foreach循环。 But since list
is an instance of GList<InnerList>
, and since a GList<InnerList>
contains instances of InnerList
(at least, I guess so), the loop should be: 但是因为list
是GList<InnerList>
一个实例,并且因为GList<InnerList>
包含InnerList
实例(至少,我猜是这样),所以循环应该是:
for (InnerList innerList : list) {
...
}
It is a syntax error and the coorect syntax would be , 这是语法错误,coorect语法是,
for(InnerList ilName : GList) {
for(InnerList ilInts : GList) {
System.out.println(ilName);
System.out.println(ilInts);
}
}
Hope this helps 希望这可以帮助
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