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。
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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).
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代码如下:
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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);
}
}
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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:
-
class Node
是非静态内部类 -
而
public static void outputThreeFormat(String[] in)
是静态方法 - 静态方法是不能直接访问非静态类的。
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。
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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);
}
}
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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
。
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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);
}
}
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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:
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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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原文链接:https://juejin.cn/post/7012086906921943048