Package org.qdl_lang.variables

Class QDLNull

java.lang.Object

org.qdl_lang.expressions.ExpressionImpl

org.qdl_lang.expressions.ConstantNode

org.qdl_lang.variables.QDLNull

All Implemented Interfaces:

Serializable, ExpressionNode, ExpressionInterface, HasResultInterface, Statement

public class QDLNull
extends ConstantNode

This represents when the user explicitly sets a variable to null. This just exists. It does nothing. Note that this is a static class -- there is exactly one null object in QDL.

Created by Jeff Gaynor
on 4/9/20 at 9:08 AM

See Also:

Serialized Form

Field Summary

Fields inherited from class org.qdl_lang.expressions.ExpressionImpl

arguments, result, valence

Fields inherited from interface org.qdl_lang.statements.ExpressionInterface

ALL_INDICES_NODE, ALT_IF_NODE, ASSIGNMENT_NODE, AXIS_RESTRICTION_NODE, CLOSED_SLICE_NODE, COMPARISON_DYAD_NODE, CONSTANT_NODE, DYAD_NODE, DYADIC_FUNCTION_REFERENCE_NODE, EXPRESSION_STEM_NODE, EXPRESSION_STEM2_NODE, FUNCTION_REFERENCE_NODE, LAMBDA_DEFINITION_NODE, LIST_NODE, MODULE_NODE, MONAD_NODE, NILAD_NODE, OPEN_SLICE_NODE, PARENTHESIZED_NODE, PARSE_EXPRESSION_BLOCK_NODE, PARSE_STATEMENT_BLOCK_NODE, POLYAD_NODE, QDL_NULL_NODE, SELECT_NODE, SET_NODE, STEM_ENTRY_NODE, STEM_EXTRACTION_NODE, STEM_NODE, UNKNOWN_NODE, VARIABLE_NODE

Method Summary

Modifier and Type	Method	Description
static QDLNull	getInstance()
int	getNodeType()	QDL is not strongly typed but Java is, so each node type should have a unique integer and conditionals should use that, not the instanceof operator.
QDLValue	getResult()
String	toString()

Methods inherited from class org.qdl_lang.expressions.ConstantNode

evaluate, makeCopy

Methods inherited from class org.qdl_lang.expressions.ExpressionImpl

addArgument, evalArg, evalLastArg, evaluatedArgs, getAlias, getArgAt, getArgCount, getArguments, getEvaluatedArgs, getLastArg, getOperatorType, getResultType, getSourceCode, getTokenPosition, hasAlias, hasEvaluatedArgs, hasTokenPosition, isEvaluated, isSizeQuery, setAlias, setArguments, setEvaluated, setEvaluatedArgs, setOperatorType, setResult, setResult, setSizeQuery, setSourceCode, setTokenPosition

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Method Detail

getInstance

public static QDLNull getInstance()

getResult

public QDLValue getResult()

Specified by:

getResult in interface HasResultInterface

Overrides:

getResult in class ExpressionImpl

toString

public String toString()

Overrides:

toString in class ExpressionImpl

getNodeType

public int getNodeType()

Description copied from interface: ExpressionInterface

QDL is not strongly typed but Java is, so each node type should have a unique integer and conditionals should use that, not the instanceof operator. This allows for efficient programming with switch statements rather than a bevy of conditionals (potentially each of which gets done even if the correct case has been handled).

Specified by:

getNodeType in interface ExpressionInterface

Overrides:

getNodeType in class ConstantNode

Returns: