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/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package parser;
import java.util.ArrayList;
import java.util.Objects;
/**
* An LR(1) item.
*
*/
public class Item implements Comparable {
private Rule rule;
/**
* Position of the stack top in the production's RHS.
*/
private int dot;
/**
* The lookahead symbol
*/
private String a;
/**
* Creates a set of items given the rule and lookahead, one item per potential
* stack position placement. The number of item is the number of symbols on
* the rhs of the rule plus one.
*
* @param rule
* @param a
* @return
*/
static ArrayList<Item> create(Rule rule, String a) {
ArrayList<Item> ret = new ArrayList<>();
final ArrayList<String> rhs = rule.getRhs();
for (int i = 0; i < rhs.size(); ++i) {
ret.add(new Item(rule, i, a));
}
ret.add(new Item(rule, rhs.size(), a));
return ret;
}
public Item(Rule rule, int dot, String a) {
this.rule = rule;
this.dot = dot;
this.a = a;
}
public Rule getRule() {
return rule;
}
public int getDot() {
return dot;
}
/**
* @return the lookahead symbol
*/
public String getA() {
return a;
}
public String getLookahead() {
return getA();
}
/**
* Returns the symbol following the stack pointer. Returns null if the pointer
* is at the end of the rhs list.
*
* @return
*/
public String getNextSymbol() {
if (dot < rule.getRhs().size()) {
return rule.getRhs().get(dot);
}
return null;
}
public String getNextNextSymbol() {
if (dot < rule.getRhs().size() - 1) {
return rule.getRhs().get(dot + 1);
}
return null;
}
public Item advance() {
return new Item(rule, dot + 1, a);
}
@Override
public int hashCode() {
int hash = 7;
hash = 37 * hash + Objects.hashCode(this.rule);
hash = 37 * hash + this.dot;
hash = 37 * hash + Objects.hashCode(this.a);
return hash;
}
@Override
public boolean equals(Object obj) {
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final Item other = (Item) obj;
if (!Objects.equals(this.rule, other.rule)) {
return false;
}
if (this.dot != other.dot) {
return false;
}
if (!Objects.equals(this.a, other.a)) {
return false;
}
return true;
}
@Override
public String toString() {
String ret = "[" + rule.getLhs() + " -> ";
final ArrayList<String> rhs = rule.getRhs();
for (int i = 0; i < dot; ++i) {
ret += rhs.get(i) + " ";
}
ret += Character.toString((char) 0x25CF);
if (dot < rhs.size()) {
ret += " ";
}
for (int i = dot; i < rhs.size(); ++i) {
ret += rhs.get(i);
if (i < rhs.size() - 1) {
ret += " ";
}
}
ret += ", " + a + "]";
return ret;
}
@Override
public int compareTo(Object o) {
return toString().compareTo(o.toString());
}
}
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