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package oracle.toplink.essentials.internal.expressions;
import java.util.*;
import oracle.toplink.essentials.expressions.*;
/**
* Used to itterate an expression tree, through inner subclasses.
*/
public abstract class ExpressionIterator {
/** Allow the iteration to build a result. */
protected Object result;
/** Some iterations require a statement. */
protected SQLSelectStatement statement;
/** Some iterations require a more general parameter. */
protected Object parameter;
/**
* Block constructor comment.
*/
public ExpressionIterator() {
super();
}
public Object getResult() {
return result;
}
public SQLSelectStatement getStatement() {
return statement;
}
/**
* Answers if this expression has already been visited.
* For a faster iteration override to insure expressions are only
* visited/processed once.
*/
public boolean hasAlreadyVisited(Expression expression) {
return false;
}
/**
* INTERNAL:
* This method must be defined by subclasses to implement the logic of the iteratation.
*/
public abstract void iterate(Expression expression);
/**
* INTERNAL:
*/
public void iterateOn(Vector expressions) {
for (Enumeration expressionEnum = expressions.elements(); expressionEnum.hasMoreElements();) {
iterate((Expression)expressionEnum.nextElement());
}
}
/**
* INTERNAL:
* Return the call.
*/
public void iterateOn(Expression expression) {
expression.iterateOn(this);
}
public void setResult(Object result) {
this.result = result;
}
public void setStatement(SQLSelectStatement statement) {
this.statement = statement;
}
/**
* Normally an Iterator will not go into the where clause of
* an SQLSubSelectExpression. I.e. when aliasing the parent statement
* is aliased before the subselects may even be normalized. An iterator to
* alias the SubSelect must be run later.
*/
public boolean shouldIterateOverSubSelects() {
return false;
}
}