org.apache.hadoop.hive.ql.lib.RuleExactMatch Maven / Gradle / Ivy
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* to you under the Apache License, Version 2.0 (the
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*
* http://www.apache.org/licenses/LICENSE-2.0
*
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*/
package org.apache.hadoop.hive.ql.lib;
import java.util.Stack;
import org.apache.hadoop.hive.ql.parse.SemanticException;
/**
* Implementation of the Rule interface for Nodes Used in Node dispatching to dispatch
* process/visitor functions for Nodes. The cost method returns 1 if there is an exact
* match between the expression and the stack, otherwise -1.
*/
public class RuleExactMatch implements SemanticRule {
private final String ruleName;
private final String[] pattern;
/**
* The rule specified as operator names separated by % symbols, the left side represents the
* bottom of the stack.
*
* E.g. TS%FIL%RS -> means
* TableScan Node followed by Filter followed by ReduceSink in the tree, or, in terms of the
* stack, ReduceSink on top followed by Filter followed by TableScan
*
* @param ruleName
* name of the rule
* @param pattern
* string specification of the rule
**/
public RuleExactMatch(String ruleName, String[] pattern) {
this.ruleName = ruleName;
this.pattern = pattern;
}
/**
* This function returns the cost of the rule for the specified stack. Returns 1 if there is
* an exact match with the entire stack, otherwise -1
*
* If any proper substack of the stack matches it will return -1. It only returns 1 if the
* entire stack matches the rule exactly.
*
* @param stack
* Node stack encountered so far
* @return cost of the function
* @throws SemanticException
*/
@Override
public int cost(Stack stack) throws SemanticException {
int numElems = (stack != null ? stack.size() : 0);
if (numElems != pattern.length) {
return -1;
}
for (int pos = numElems - 1; pos >= 0; pos--) {
if(!stack.get(pos).getName().equals(pattern[pos])) {
return -1;
}
}
return numElems;
}
/**
* @return the name of the Node
**/
@Override
public String getName() {
return ruleName;
}
}