java中调用scala

案例

说明：主要参照spark源码

编写scala类及半生对象

package org.apache.spark.sql.types

import org.apache.spark.annotation.Stable

/**
 * The data type representing `NULL` values. Please use the singleton `DataTypes.NullType`.
 *
 * @since 1.3.0
 */
@Stable
class NullType private() extends DataType {
  // The companion object and this class is separated so the companion object also subclasses
  // this type. Otherwise, the companion object would be of type "NullType$" in byte code.
  // Defined with a private constructor so the companion object is the only possible instantiation.
  override def defaultSize: Int = 1

  private[spark] override def asNullable: NullType = this
}

/**
 * @since 1.3.0
 */
@Stable
case object NullType extends NullType

在java中调用scala

package org.apache.spark.sql.types;

import java.util.*;

import org.apache.spark.annotation.Stable;

/**
 * To get/create specific data type, users should use singleton objects and factory methods
 * provided by this class.
 *
 * @since 1.3.0
 */
@Stable
public class DataTypes {
  /**
   * Gets the NullType object.
   */
  public static final DataType NullType = NullType$.MODULE$;