異常

前言. 開發時候遇到內部類的問題.

• 異常

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).

• 代碼如下

// 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;}}// 繼承方法的形式進行運行.// 特別注意 局部類 No enclosing instance of type XXX is accessible. Must qualify 異常.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;}

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解決措施

• 方法1
  將局部類設置為靜態的. 類名前添加<static>關鍵字即可.

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

• 方法2
  通過類名.局部類名訪問即可. 即如下的new ParentClassName().new GetLength().

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

• 方法3
  不使用局部類即可. 作為非public類型類寫在一個文件即可.

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Reference

[1] JAVA在編寫內部類時No enclosing instance of type XXX is accessible. Must qualify原因及解決.
[2] No enclosing instance of type 類名 is accessible. Must qualify the allocation with.

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