com.metamatrix.query.sql.symbol
Class Constant

java.lang.Object
  com.metamatrix.query.sql.symbol.Constant

All Implemented Interfaces:

LanguageObject, Expression, java.io.Serializable, java.lang.Cloneable, java.lang.Comparable

public class Constant
extends java.lang.Object
implements Expression, java.lang.Comparable

This class represents a literal value in a SQL string. The Constant object has a value and a type for that value. In many cases, the type can be derived from the type of the value, but that is not true if the value is null. In that case, the type is unknown and is set to the null type until the type is resolved at a later point.

See Also:

Serialized Form

Constructor Summary

Constant(java.lang.Object value)
Construct a constant with a value, which may be null.

Constant(java.lang.Object value, java.lang.Class type)
Construct a typed constant.

Method Summary

void	acceptVisitor(LanguageVisitor visitor) Method for accepting a visitor.
java.lang.Object	clone() Return a shallow copy of this object - value is NOT cloned!
int	compareTo(java.lang.Object o)
boolean	equals(java.lang.Object obj) Compare this constant to another constant for equality.
java.lang.Class	getType() Get type of constant, if known
java.lang.Object	getValue() Get value of constant
int	hashCode() Define hash code to be that of the underlying object to make it stable.
boolean	isNull() Return true if the constant is null.
boolean	isResolved() Return true if expression has been fully resolved.
java.lang.String	toString() Return a String representation of this object using SQLStringVisitor.

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

Constant

public Constant(java.lang.Object value,
                java.lang.Class type)

Construct a typed constant. The specified value is not verified to be a value of the specified type. If this is not true, stuff probably won't work later on.

Parameters:

value - Constant value, may be null

type - Type for the constant, should never be null

Constant

public Constant(java.lang.Object value)

Construct a constant with a value, which may be null. The data type is determined automatically from the type of the value.

Parameters:

value - Constant value, may be null

Method Detail

getType

public java.lang.Class getType()

Get type of constant, if known

Specified by:

getType in interface Expression

Returns:

Java class name of type

getValue

public java.lang.Object getValue()

Get value of constant

Returns:

Constant value

isNull

public boolean isNull()

Return true if the constant is null.

Returns:

True if value is null

isResolved

public boolean isResolved()

Return true if expression has been fully resolved. Typically the QueryResolver component will handle resolution of an expression.

Specified by:

isResolved in interface Expression

Returns:

True if resolved

acceptVisitor

public void acceptVisitor(LanguageVisitor visitor)

Description copied from interface: LanguageObject

Method for accepting a visitor. It is the responsibility of the language object to call back on the visitor.

Specified by:

acceptVisitor in interface LanguageObject

Parameters:

visitor - Visitor being used

equals

public boolean equals(java.lang.Object obj)

Compare this constant to another constant for equality.

Overrides:

equals in class java.lang.Object

Parameters:

obj - Other object

Returns:

True if constants are equal

hashCode

public int hashCode()

Define hash code to be that of the underlying object to make it stable.

Overrides:

hashCode in class java.lang.Object

Returns:

Hash code, based on value

clone

public java.lang.Object clone()

Return a shallow copy of this object - value is NOT cloned!

Specified by:

clone in interface LanguageObject

Overrides:

clone in class java.lang.Object

Returns:

Shallow copy of object

toString

public java.lang.String toString()

Return a String representation of this object using SQLStringVisitor.

Overrides:

toString in class java.lang.Object

Returns:

String representation using SQLStringVisitor

compareTo

public int compareTo(java.lang.Object o)
              throws java.lang.ClassCastException

Specified by:

compareTo in interface java.lang.Comparable

Throws:

java.lang.ClassCastException

Since:

4.2

See Also:

Comparable.compareTo(java.lang.Object)