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[Java教程]Java解决No enclosing instance of type PrintListFromTailToHead is accessible问题


今天在编译Java程序时遇到如下问题:

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).

源代码为:

 

 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("结果是:" + 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 }

 

问题解释:

代码中,我的ListNode类是定义在PrintListFromTailToHead类中的内部类。ListNode内部类是动态的内部类,而我的main方法是static静态的。

就好比静态的方法不能调用动态的方法一样。

有两种解决办法:

第一种:

将内部类ListNode定义成静态static的类。

第二种:

将内部类ListNode在PrintListFromTailToHead类外边定义。

 

两种解决方法:

第一种:

 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("结果是:" + 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   }

第二种:

 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 }