QDLNull (QDL root module 1.5.6 API)

java.lang.Object
- edu.uiuc.ncsa.qdl.expressions.ExpressionImpl
- - edu.uiuc.ncsa.qdl.expressions.ConstantNode
  - - edu.uiuc.ncsa.qdl.variables.QDLNull

All Implemented Interfaces:

ExpressionNode, ExpressionInterface, HasResultInterface, Statement, Serializable
```
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 edu.uiuc.ncsa.qdl.expressions.ExpressionImpl
  arguments, result, valence
- Fields inherited from interface edu.uiuc.ncsa.qdl.statements.ExpressionInterface
  ALL_INDICES_NODE, ALT_IF_NODE, ASSIGNMENT_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

All Methods Static Methods Instance Methods Concrete Methods
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.
`String`	`toString()`

Methods inherited from class edu.uiuc.ncsa.qdl.expressions.ConstantNode
evaluate, makeCopy

Methods inherited from class edu.uiuc.ncsa.qdl.expressions.ExpressionImpl
evalArg, evalLastArg, evaluatedArgs, getAlias, getArgAt, getArgCount, getArguments, getEvaluatedArgs, getLastArg, getOperatorType, getResult, getResultType, getSourceCode, getTokenPosition, hasAlias, hasEvaluatedArgs, hasTokenPosition, isEvaluated, isSizeQuery, setAlias, setArguments, setEvaluated, setEvaluatedArgs, setOperatorType, setResult, setResultType, 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()
```
  - 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: