org.apache.lucene.search

## Class Query

- java.lang.Object
- - org.apache.lucene.search.Query

- Direct Known Subclasses:
    BlendedTermQuery, BooleanQuery, BoostQuery, ConstantScoreQuery, DisjunctionMaxQuery, DocValuesFieldExistsQuery, IndexOrDocValuesQuery, MatchAllDocsQuery, MatchNoDocsQuery, MultiPhraseQuery, MultiTermQuery, NGramPhraseQuery, NormsFieldExistsQuery, PhraseQuery, PointInSetQuery, PointRangeQuery, SpanQuery, SynonymQuery, TermInSetQuery, TermQuery

      public abstract class Query
      extends Object

  The abstract base class for queries.

  Instantiable subclasses are:

  - `TermQuery`
  - `BooleanQuery`
  - `WildcardQuery`
  - `PhraseQuery`
  - `PrefixQuery`
  - `MultiPhraseQuery`
  - `FuzzyQuery`
  - `RegexpQuery`
  - `TermRangeQuery`
  - `PointRangeQuery`
  - `ConstantScoreQuery`
  - `DisjunctionMaxQuery`
  - `MatchAllDocsQuery`

  See also the family of `Span Queries` and additional queries available in the Queries module

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `Query()`

  - ### Method Summary

    All Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected int` | `classHash()` Provides a constant integer for a given class, derived from the name of the class.
    `Weight` | `createWeight(IndexSearcher searcher, boolean needsScores, float boost)` Expert: Constructs an appropriate Weight implementation for this query.
    `abstract boolean` | `equals(Object obj)` Override and implement query instance equivalence properly in a subclass.
    `abstract int` | `hashCode()` Override and implement query hash code properly in a subclass.
    `Query` | `rewrite(IndexReader reader)` Expert: called to re-write queries into primitive queries.
    `protected boolean` | `sameClassAs(Object other)` Utility method to check whether `other` is not null and is exactly of the same class as this object's class.
    `String` | `toString()` Prints a query to a string.
    `abstract String` | `toString(String field)` Prints a query to a string, with `field` assumed to be the default field and omitted.

    - ### Methods inherited from class java.lang.Object

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### Query

          public Query()

  - ### Method Detail

    - #### toString

          public abstract String toString(String field)

      Prints a query to a string, with `field` assumed to be the default field and omitted.

    - #### toString

          public final String toString()

      Prints a query to a string.
      Overrides:
        `toString` in class `Object`

    - #### createWeight

          public Weight createWeight(IndexSearcher searcher,
                                     boolean needsScores,
                                     float boost)
                              throws IOException

      Expert: Constructs an appropriate Weight implementation for this query.

      Only implemented by primitive queries, which re-write to themselves.

      Parameters:
        `needsScores` - True if document scores (`Scorer.score()`) are needed.
        `boost` - The boost that is propagated by the parent queries.
      Throws:
        `IOException`

    - #### rewrite

          public Query rewrite(IndexReader reader)
                        throws IOException

      Expert: called to re-write queries into primitive queries. For example, a PrefixQuery will be rewritten into a BooleanQuery that consists of TermQuerys.
      Throws:
        `IOException`

    - #### equals

          public abstract boolean equals(Object obj)

      Override and implement query instance equivalence properly in a subclass. This is required so that `QueryCache` works properly. Typically a query will be equal to another only if it's an instance of the same class and its document-filtering properties are identical that other instance. Utility methods are provided for certain repetitive code.
      Overrides:
        `equals` in class `Object`
      See Also:
        `sameClassAs(Object)`, `classHash()`

    - #### hashCode

          public abstract int hashCode()

      Override and implement query hash code properly in a subclass. This is required so that `QueryCache` works properly.
      Overrides:
        `hashCode` in class `Object`
      See Also:
        `equals(Object)`

    - #### sameClassAs

          protected final boolean sameClassAs(Object other)

      Utility method to check whether `other` is not null and is exactly of the same class as this object's class. When this method is used in an implementation of `equals(Object)`, consider using `classHash()` in the implementation of `hashCode()` to differentiate different class

    - #### classHash

          protected final int classHash()

      Provides a constant integer for a given class, derived from the name of the class. The rationale for not using just `Object.hashCode()` is that classes may be assigned different hash codes for each execution and we want hashes to be possibly consistent to facilitate debugging.

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