Package edu.caltech.nanodb.expressions

Class ColumnValue

  • All Implemented Interfaces:
    java.lang.Cloneable
    public class ColumnValue
extends Expression
    This expression class represents the value of a tuple column. The column name is stored in the expression object, and the actual value of the column is looked up during evaluation time.

    • Field Detail

      • columnName

        private ColumnName columnName
        The name of the column.

    • Constructor Detail

      • ColumnValue

        public ColumnValue​(ColumnName columnName)
        Initialize a new column-value expression object with the specified column-name.
        Parameters:
        columnName - the name of the column to retrieve the value for

    • Method Detail

      • getColumnName

        public ColumnName getColumnName()
        Returns the column name object
        Returns:
        the column name object

      • setColumnName

        public void setColumnName​(ColumnName columnName)
        Sets the column name object
        Parameters:
        columnName - the new column name object

      • getColumnInfo

        public ColumnInfo getColumnInfo​(Schema schema)
                         throws SchemaNameException
        Description copied from class: Expression
        Returns a ColumnInfo object describing the type (and possibly the name) of the expression's result.
        Specified by:
        getColumnInfo in class Expression
        Parameters:
        schema - a schema object that can be used to look up name and type details for symbols referenced by the expression.
        Returns:
        a column-information object describing the type (and possibly the name and table-name) of this expression's result
        Throws:
        SchemaNameException - if a symbol cannot be resolved, either because it doesn't appear in the schema, or because the name is ambiguous.

      • evaluate

        public java.lang.Object evaluate​(Environment env)
                          throws ExpressionException
        Description copied from class: Expression
        Evaluates this expression object in the context of the specified environment. The environment provides any external information necessary to evaluate the expression, such as the current tuples loaded from tables referenced within the expression.
        Specified by:
        evaluate in class Expression
        Parameters:
        env - the environment to look up symbol-values from, when evaluating the expression
        Returns:
        the result of the expression evaluation
        Throws:
        ExpressionException - if the expression cannot be evaluated for some reason.

      • traverse

        public Expression traverse​(ExpressionProcessor p)
        Description copied from class: Expression

        This method allows the entire expression tree to be traversed node by node, either for analysis or for transformation. The ExpressionProcessor instance receives notifications as each node in the expression is entered and left.

        The expression tree can also be manipulated by this traversal process, depending on what the ExpressionProcessor wants to do. If the expression node that traverse() is invoked on, needs to be replaced with a new expression node, the replacement is returned by the traverse() method. (The ExpressionProcessor specifies the replacement as the return-value from the ExpressionProcessor.leave(Expression) method.)

        Specified by:
        traverse in class Expression
        Parameters:
        p - the object that performs analysis or transformation of the expression tree
        Returns:
        an Expression node to replace this node, or null if no changes are to be made.

      • toString

        public java.lang.String toString()
        Overrides:
        toString in class java.lang.Object

      • simplify

        public Expression simplify()
        Column values cannot be simplified any further, so this method just returns the expression it's called on.
        Overrides:
        simplify in class Expression
        Returns:
        a reference to an expression, either a simplified version of this expression, or the original unmodified expression

      • equals

        public boolean equals​(java.lang.Object obj)
        Checks if the argument is an expression with the same structure, but not necessarily the same references.
        Specified by:
        equals in class Expression
        Parameters:
        obj - the object to which we are comparing

      • hashCode

        public int hashCode()
        Computes the hashcode of an Expression. This method is used to see if two expressions might be equal.
        Specified by:
        hashCode in class Expression

      • clone

        protected java.lang.Object clone()
                          throws java.lang.CloneNotSupportedException
        Creates a copy of expression.
        Overrides:
        clone in class Expression
        Throws:
        java.lang.CloneNotSupportedException