异常: No enclosing instance of type xx is accessible. Must qualify (Java 内部类)

深藏阁楼爱情的钟 2023-02-22 12:08 2阅读 0赞

### 异常 ###

前言. 开发时候遇到内部类的问题.

*  异常

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

*  代码如下

// 注意 
    	static class GetLength implements Function<String, Integer> {
    		public Integer call(String s) {
    			return s.length();
    		}
    	}
    
    	class Sum implements Function2<Integer, Integer, Integer> {
    		public Integer call(Integer a, Integer b) {
    			return a + b;
    		}
    	}
    
    	// 继承方法的形式进行运行.
    	// 特别注意 局部类 No enclosing instance of type XXX is accessible. Must qualify 异常.
    	static int getTotalLengthByExtendsFunction(JavaSparkContext context) {
    
    		int totalLength = 0;
    		if (null != context) {
    
    			JavaRDD<String> distFile = context.textFile("data/wordcount/spark-overview.txt");
    			JavaRDD<Integer> linesRDD = distFile.map(new GetLength());
    			totalLength = linesRDD.reduce(new Sum());
    		}
    		return totalLength;
    
    	}

--------------------

### 解决措施 ###

*  方法1  
    将局部类设置为静态的. 类名前添加`<static>`关键字即可.

static class Sum implements Function2<Integer, Integer, Integer> {
    		public Integer call(Integer a, Integer b) {
    			return a + b;
    		}
    	}

*  方法2  
    通过`类名.局部类名`访问即可. 即如下的`new ParentClassName().new GetLength()`.

JavaRDD<Integer> linesRDD = distFile.map(new ParentClassName().new GetLength());

*  方法3  
    不使用局部类即可. 作为非`public`类型类写在一个文件即可.

--------------------

### Reference ###

\[1\] [JAVA在编写内部类时No enclosing instance of type XXX is accessible. Must qualify原因及解决.][JAVA_No enclosing instance of type XXX is accessible. Must qualify_.]  
\[2\] [No enclosing instance of type 类名 is accessible. Must qualify the allocation with.][No enclosing instance of type _ is accessible. Must qualify the allocation with.]

[JAVA_No enclosing instance of type XXX is accessible. Must qualify_.]: https://blog.csdn.net/wh445306/article/details/101020066
[No enclosing instance of type _ is accessible. Must qualify the allocation with.]: https://blog.csdn.net/qq_41885010/article/details/80516284