Java 枚举类型(enum)的一个不常见用法

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/** Specifies whether and how a field should be indexed. */ public static enum Index { /** Do not index the field value. This field can thus not be searched, * but one can still access its contents provided it is * {@link Field.Store stored}. */ NO { @Override public boolean isIndexed() { return false; } @Override public boolean isAnalyzed() { return false; } @Override public boolean omitNorms() { return true; } }, /** Index the tokens produced by running the field's * value through an Analyzer. This is useful for * common text. */ ANALYZED { @Override public boolean isIndexed() { return true; } @Override public boolean isAnalyzed() { return true; } @Override public boolean omitNorms() { return false; } }, /** Index the field's value without using an Analyzer, so it can be searched. * As no analyzer is used the value will be stored as a single term. This is * useful for unique Ids like product numbers. */ NOT_ANALYZED { @Override public boolean isIndexed() { return true; } @Override public boolean isAnalyzed() { return false; } @Override public boolean omitNorms() { return false; } }, public abstract boolean isIndexed(); public abstract boolean isAnalyzed(); public abstract boolean omitNorms(); }