Github user mgaido91 commented on a diff in the pull request:

    https://github.com/apache/spark/pull/21026#discussion_r180749769
  
    --- Diff: 
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/javaCode.scala
 ---
    @@ -0,0 +1,166 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one or more
    + * contributor license agreements.  See the NOTICE file distributed with
    + * this work for additional information regarding copyright ownership.
    + * The ASF licenses this file to You under the Apache License, Version 2.0
    + * (the "License"); you may not use this file except in compliance with
    + * the License.  You may obtain a copy of the License at
    + *
    + *    http://www.apache.org/licenses/LICENSE-2.0
    + *
    + * Unless required by applicable law or agreed to in writing, software
    + * distributed under the License is distributed on an "AS IS" BASIS,
    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    + * See the License for the specific language governing permissions and
    + * limitations under the License.
    + */
    +
    +package org.apache.spark.sql.catalyst.expressions.codegen
    +
    +import java.lang.{Boolean => JBool}
    +
    +import scala.language.{existentials, implicitConversions}
    +
    +import org.apache.spark.sql.types.{BooleanType, DataType}
    +
    +/**
    + * Trait representing an opaque fragments of java code.
    + */
    +trait JavaCode {
    +  def code: String
    +  override def toString: String = code
    +}
    +
    +/**
    + * Utility functions for creating [[JavaCode]] fragments.
    + */
    +object JavaCode {
    +  /**
    +   * Create a java literal.
    +   */
    +  def literal(v: String, dataType: DataType): LiteralValue = dataType 
match {
    +    case BooleanType if v == "true" => TrueLiteral
    +    case BooleanType if v == "false" => FalseLiteral
    +    case _ => new LiteralValue(v, CodeGenerator.javaClass(dataType))
    +  }
    +
    +  /**
    +   * Create a default literal. This is null for reference types, false for 
boolean types and
    +   * -1 for other primitive types.
    +   */
    +  def defaultLiteral(dataType: DataType): LiteralValue = {
    +    new LiteralValue(
    +      CodeGenerator.defaultValue(dataType, typedNull = true),
    +      CodeGenerator.javaClass(dataType))
    +  }
    +
    +  /**
    +   * Create a local java variable.
    +   */
    +  def variable(name: String, dataType: DataType): VariableValue = {
    +    variable(name, CodeGenerator.javaClass(dataType))
    +  }
    +
    +  /**
    +   * Create a local java variable.
    +   */
    +  def variable(name: String, javaClass: Class[_]): VariableValue = {
    +    VariableValue(name, javaClass)
    +  }
    +
    +  /**
    +   * Create a local isNull variable.
    +   */
    +  def isNullVariable(name: String): VariableValue = variable(name, 
BooleanType)
    --- End diff --
    
    yes, I see the goal of this, but I can't understand why it is useful. The 
isNull variable is a boolean as all the other boolean variables... It is the 
more frequent case, but I can't see any differentiation between them and other 
booleans. Do you have in mind a case for which this differentiation can be 
useful?


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