Package com.inductiveautomation.ignition.common.expressions

Interface Expression

All Known Implementing Classes:
AbstractAlertExpressionContext.AlertVariableExpression, AbstractExpression, AlarmEventPropertyExpression, ArithmeticExpression, BitwiseExpression, BitwiseNot, BoundPropertyExpression, BoundPropertyExpression, BoundTagExpression, BoundVariableExpression, ComparisonExpression, ConstantExpression, EqualityExpression, FormattedExpression, FunctionExpression, LikeExpression, LocaleAwareMessageParseContext.LocaleStringExpression, LogicalExpression, NonLocalizedToStringExpression, NotExpression, PropertyBasedExpressionParseContext.PropertyReferenceExpression, SubscriptExpression, TagPathReadExpression, TagReferenceBinder.SubscribedTagExpression, TagReferenceBinder.TagReadExpression, ToStringExpression, UMinusExpression
public interface Expression
An expression is something that can be executed to compute a result. Each instance of expression is typically some node in what amounts to a parse tree. Many expressions such as operators and function calls have child expressions.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    connect(CommonContext context, InteractionListener updateListener)
    Gives the expression a chance to connect itself to things, if necessary.
    void
    disconnect()
    Tells the expression to disconnect from anything it was connected to.
    @NonNull QualifiedValue
    execute()
    Compute and return the value of this expression.
    Expression[]
    getChildren()
    The children (if any) that this expression is dependent on for its execution.
    String
    getOpName()
    Return a human-readable name for the operation that this expression performs.
    default Class<?>
    getType()
    Return the type that this expression will return.
    void
    shutdown()
    Tells the expression to shutdown any polling operations.
    void
    startup()
    Tells the expression to startup any polling operations.

  • Method Details

    • execute

      @NonNull QualifiedValue execute() throws ExpressionException
      Compute and return the value of this expression.
      Returns:
      the result of the expression evaluation as a QualifiedValue
      Throws:
      ExpressionException - if an error occurs during execution

    • getType

      default Class<?> getType()
      Return the type that this expression will return.
      Returns:
      the Class of the value returned by execute()

    • getOpName

      String getOpName()
      Return a human-readable name for the operation that this expression performs.
      Returns:
      the operation name

    • getChildren

      Expression[] getChildren()
      The children (if any) that this expression is dependent on for its execution.
      Returns:
      an array of child Expressions, or an empty array if no children exist

    • connect

      void connect(CommonContext context, InteractionListener updateListener)
      Gives the expression a chance to connect itself to things, if necessary. Most expressions do not have any connections. An expression should notify the updateListener if they change.
      Parameters:
      context - the CommonContext used to look up external resources
      updateListener - the InteractionListener to notify when the expression value changes

    • disconnect

      void disconnect()
      Tells the expression to disconnect from anything it was connected to.

    • startup

      void startup()
      Tells the expression to startup any polling operations. Expressions that use this can remember the updateListener from connect() to feed update notification to.

    • shutdown

      void shutdown()
      Tells the expression to shutdown any polling operations.