如何使用每种类型的循环迭代通用列表

Question

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.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".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);
        }
    }       
}   

有人可以帮我理解为什么当集合应该是可迭代的时候GList不被认为是java.lang.iterable的一个实例？

谢谢.

Answer 1

它不被视为实例,java.lang.Iterable因为它没有实现接口java.lang.Iterable.就如此容易.将其声明更改为

public class GList<T> implements Iterable<T>

你会很乐意使用它的foreach循环.但是因为list是一个实例GList<InnerList>,并且由于GList<InnerList>包含实例InnerList(至少,我猜是这样),循环应该是:

for (InnerList innerList : list) {
    ...
}