Java解決No enclosing instance of type PrintListFromTailToHead is accessible問題，enclosinginstance

Java解決No enclosing instance of type PrintListFromTailToHead is accessible問題，enclosinginstance

今天在編譯Java程式時遇到如下問題：

No enclosing instance of type PrintListFromTailToHead is accessible. Must qualify the allocation with an enclosing instance
of type PrintListFromTailToHead (e.g. x.new A() where x is an instance of PrintListFromTailToHead).

原始碼為：

 

 1 public class PrintListFromTailToHead { 2  3     public static void main(String[] args) { 4         ListNode one = new ListNode(1); 5         ListNode two = new ListNode(2); 6         ListNode three = new ListNode(3); 7         one.next = two; 8         two.next = three; 9         10         ArrayList<Integer> result = printListFromTailToHead(one);11 12         System.out.println("結果是：" + result);13     }14     15      class ListNode {16 17         public int val;18         public ListNode next;19 20         public ListNode() {21 22         }23 24         public ListNode(int val) {25             this.val = val;26         }27     }28 29     public static ArrayList<Integer> printListFromTailToHead(ListNode listNode) {30 31         Stack<Integer> stack = new Stack<Integer>();32         while (listNode != null) {33             stack.push(listNode.val);34             listNode = listNode.next;35         }36 37         ArrayList<Integer> arrayList = new ArrayList<Integer>();38         while (!stack.isEmpty()) {39             arrayList.add(stack.pop());40         }41         return arrayList;42     }   45 }

 

問題解釋：

代碼中，我的ListNode類是定義在PrintListFromTailToHead類中的內部類。ListNode內部類是動態內部類，而我的main方法是static靜態。

就好比靜態方法不能調用動態方法一樣。

有兩種解決辦法：

第一種：

將內部類ListNode定義成靜態static的類。

第二種：

將內部類ListNode在PrintListFromTailToHead類外邊定義。

 

兩種解決方案：

第一種：

 1 public class PrintListFromTailToHead { 2  3     public static void main(String[] args) { 4         ListNode one = new ListNode(1); 5         ListNode two = new ListNode(2); 6         ListNode three = new ListNode(3); 7         one.next = two; 8         two.next = three; 9         10         ArrayList<Integer> result = printListFromTailToHead(one);11 12         System.out.println("結果是：" + result);13     }14     15     static class ListNode {16 17         public int val;18         public ListNode next;19 20         public ListNode() {21 22         }23 24         public ListNode(int val) {25             this.val = val;26         }27     }

第二種：

 1 public class PrintListFromTailToHead { 2  3     public static void main(String[] args) { 4         ListNode one = new ListNode(1); 5         ListNode two = new ListNode(2); 6         ListNode three = new ListNode(3); 7         one.next = two; 8         two.next = three; 9     }10 11         public static ArrayList<Integer> printListFromTailToHead(ListNode listNode) {12 13         Stack<Integer> stack = new Stack<Integer>();14         while (listNode != null) {15             stack.push(listNode.val);16             listNode = listNode.next;17         }18 19         ArrayList<Integer> arrayList = new ArrayList<Integer>();20         while (!stack.isEmpty()) {21             arrayList.add(stack.pop());22         }23         return arrayList;24     }25 }26 27 class ListNode {28 29     public int val;30     public ListNode next;31 32     public ListNode() {33 34     }35 36     public ListNode(int val) {37         this.val = val;38     }39 }