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解决Java错误No enclosing instance of type XXX is accessible 解决Java变异出现错误No enclosing instance of type XX

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一、错误代码和错误现象

先记录下问题现象,写java代码时遇到下面的编译错误。

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

代码如下:

import java.util.Arrays;
import java.util.LinkedHashMap;

public class FileTree {
 class Node {
  String name;

  public Node(String name) {
   super();
   this.name = name;
  }

  LinkedHashMap<String, Node> map = new LinkedHashMap<String, Node>();
 }

 public static void outputThreeFormat(String[] in) {
  Arrays.sort(in);
  Node root = new Node("/");

 }

 public static void main(String[] args) {
  String[] in = { "usr/local/lib64", "GAMES",
    "usr/DRIVERS", "home", "var/log/" };
  outputThreeFormat(in);

 }

}

错误截图如下:

二、如何解决这些错误

错误的含义是,没有可以访问的外部实例enclosing instance。必须分配一个合适的外部类FileTree的实例(如x.new A(),x必须是FileTree的实例。)

结合出错的代码,很容易知道根源是什么:

1、可以不使用内部类

可以把class Node作为外部类定义,这样在FileTree类中不管是静态还是非静态方法都可以直接new Node初始化个节点。

import java.util.Arrays;
import java.util.LinkedHashMap;

class Node {
 String name;

 public Node(String name) {
  super();
  this.name = name;
 }

 LinkedHashMap<String, Node> map = new LinkedHashMap<String, Node>();
}

public class FileTree {

 public static void outputThreeFormat(String[] in) {
  Arrays.sort(in);
  Node root = new Node("/");

 }

 public static void main(String[] args) {
  String[] in = { "usr/local/lib64", "GAMES", "usr/DRIVERS", "home", "var/log/" };
  outputThreeFormat(in);

 }

}

2、可以使用静态内部类

可以把class Node作为静态内部类定义,即static class Node

import java.util.Arrays;
import java.util.LinkedHashMap;

public class FileTree {
 static class Node {
  String name;

  public Node(String name) {
   super();
   this.name = name;
  }

  LinkedHashMap<String, Node> map = new LinkedHashMap<String, Node>();
 }

 public static void outputThreeFormat(String[] in) {
  Arrays.sort(in);
  Node root = new Node("/");

 }

 public static void main(String[] args) {
  String[] in = { "usr/local/lib64", "GAMES",
    "usr/DRIVERS", "home", "var/log/" };
  outputThreeFormat(in);

 }

}

3、使用非静态内部类时,使用外部类的实例进行调用

如下所示:

import java.util.Arrays;
import java.util.LinkedHashMap;

public class FileTree {
 class Node {
  String name;

  public Node(String name) {
   super();
   this.name = name;
  }

  LinkedHashMap<String, Node> map = new LinkedHashMap<String, Node>();
 }

 public static void outputThreeFormat(String[] in) {
  Arrays.sort(in);
  FileTree ft=new FileTree();
  Node root = ft.new Node("/");

 }

 public static void main(String[] args) {
  String[] in = { "usr/local/lib64", "GAMES",
    "usr/DRIVERS", "home", "var/log/" };
  outputThreeFormat(in);

 }

}

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