Java 神秘的零指针
我一直在做一个项目，在这个项目中，我用Backus–Naur格式的语法符号获取一个文件，并用它生成句子。这是我正在处理的BNF文件：Java 神秘的零指针,java,arrays,recursion,Java,Arrays,Recursion,我一直在做一个项目，在这个项目中，我用Backus–Naur格式的语法符号获取一个文件，并用它生成句子。这是我正在处理的BNF文件： <s>::=<np> <vp> <np>::=<dp> <adjp> <n>|<pn> <pn>::=John|Jane|Sally|Spot|Fred|Elmo <adjp>::=<adj>|<adj> <adjp
<s>::=<np> <vp>
<np>::=<dp> <adjp> <n>|<pn>
<pn>::=John|Jane|Sally|Spot|Fred|Elmo
<adjp>::=<adj>|<adj> <adjp>
<adj>::=big|fat|green|wonderful|faulty|subliminal|pretentious
<dp>::=the|a
<n>::=dog|cat|man|university|father|mother|child|television
<vp>::=<tv> <np>|<iv>
<tv>::=hit|honored|kissed|helped
<iv>::=died|collapsed|laughed|wept
：=
::= |
：：=John | Jane | Sally | Spot | Fred | Elmo
::=|
：：=大|胖|绿|棒|错|潜意识|自命不凡
：=a
：：=狗|猫|人|大学|父亲|母亲|孩子|电视
::= |
：：=击中|荣誉|亲吻|帮助
：：=死了|倒了|笑了|哭了
import java.util.*;
import java.util.regex.*;
class GrammarSolver {
//Create output variable for sentences
String output = "";
//Create a map for storing grammar
SortedMap<String, String[]> rules = new TreeMap<String, String[]>();
//Create a queue for managing sentences
Queue<String> queue = new LinkedList<String>();
/**
* Constructor for GrammarSolver
*
* Accepts a List<String> then processes it splitting
* BNF notation into a TreeMap so that "A ::= B" is
* loaded into the tree so the key is A and the data
* contained is B
*
* @param grammar List of Strings with a set of
* grammar rules in BNF form.
*/
public GrammarSolver(List<String> grammar){
//Convert list to string
String s = grammar.toString();
//Split and clean
String[] parts = s.split("::=|,");
for(int i = 0; i < parts.length; i++){
parts[i] = parts[i].trim();
parts[i] = parts[i].replaceAll("\\[|]", "");
//parts[i] = parts[i].replaceAll("[ \t]+", "");
}
//Load into TreeMap
for(int i = 0; i < parts.length - 1; i+=2){
String[] temp = parts[i+1].split("\\|");
rules.put(parts[i], temp);
}
//Debug
String[] test = generate("<s>", 2);
System.out.println(test[0]);
System.out.println(test[1]);
}
/**
* Method to check if a certain non-terminal (such as <adj>
* is present in the map.
*
* Accepts a String and returns true if said non-terminal is
* in the map, and therefore a valid grammar. Returns false
* otherwise.
*
* @param symbol The string that will be checked
* @return boolean True if present, false if otherwise
*/
public boolean grammarContains(String symbol){
if(rules.keySet().toString().contains(symbol)){
return true;
}else{
return false;
}
}
/**
* Method to generate sentences based on BNF notation and
* return them as strings.
*
* @param symbol The BNF symbol to be generated
* @param times The number of sentences to be generated
* @return String The generated sentence
*/
public String[] generate(String symbol, int times){
//Array for output
String[] output = new String[times];
for(int i = 0; i < times; i++){
//Clear array for run
output[i] = "";
//Grab rules, and store in an array
lString[] grammar = rules.get(symbol);
//Generate random number and assign to var
int rand = randomNumber(grammar.length);
//Take chosen grammar and split into array
String[] rules = grammar[rand].toString().split("\\s");
//Determine if the rule is terminal or not
if(grammarContains(rules[0])){
//System.out.println("grammar has more grammars");
//Find if there is one or more conditions
if(rules.length == 1){
String[] returnString = generate(rules[0], 1);
output[i] += returnString[0];
output[i] += " ";
}else if(rules.length > 1){
for(int j = 0; j < rules.length; j++){
String[] returnString = generate(rules[j], 1);
output[i] += returnString[0];
output[i] += " ";
}
}
}else{
String[] returnArr = new String[1];
returnArr[0] = grammar[rand];;
return returnArr;
}
output[i] = output[i].trim();
}
return output;
}
/**
* Method to list all valid non-terminals for the current grammar
*
* @return String A listing of all valid non-terminals
* contained in the current grammar that
* can be used to generate words or
* sentences.
*/
String getSymbols(){
return rules.keySet().toString();
}
public int randomNumber(int max){
Random rand = new Random();
int returnVal = rand.nextInt(max);
return returnVal;
}
}
import java.io.*;
import java.util.*;
public class GrammarTest {
public static void main(String[] args) throws FileNotFoundException {
Scanner console = new Scanner(System.in);
System.out.println();
// open grammar file
Scanner input = new Scanner(new File("sentence.txt"));
// read the grammar file and construct the grammar solver
List<String> grammar = new ArrayList<String>();
while (input.hasNextLine()) {
String next = input.nextLine().trim();
if (next.length() > 0)
grammar.add(next);
}
GrammarSolver solver =
new GrammarSolver(Collections.unmodifiableList(grammar));
}
}
import java.util.*；
导入java.util.regex.*；
类语法工具{
//为句子创建输出变量
字符串输出=”；
//创建用于存储语法的映射
SortedMap规则=新树映射（）；
//创建用于管理句子的队列
Queue Queue=new LinkedList（）；
/**
*GrammarSolver的构造函数
*
*接受一个列表，然后处理它
*将BNF符号转换成树形图，这样“a:：=B”是
*加载到树中，使键为
*包含的是B
*
*@param语法字符串列表，包含一组
*BNF形式的语法规则。
*/
公共语法Solver（列表语法）{
//将列表转换为字符串
字符串s=语法.toString（）；
//干干净净
字符串[]部分=s.split（“：：=|，”；
对于（int i=0；i1）{
对于（int j=0；j import java.util.*;
import java.util.regex.*;
class GrammarSolver {
//Create output variable for sentences
String output = "";
//Create a map for storing grammar
SortedMap<String, String[]> rules = new TreeMap<String, String[]>();
//Create a queue for managing sentences
Queue<String> queue = new LinkedList<String>();
/**
* Constructor for GrammarSolver
*
* Accepts a List<String> then processes it splitting
* BNF notation into a TreeMap so that "A ::= B" is
* loaded into the tree so the key is A and the data
* contained is B
*
* @param grammar List of Strings with a set of
* grammar rules in BNF form.
*/
public GrammarSolver(List<String> grammar){
//Convert list to string
String s = grammar.toString();
//Split and clean
String[] parts = s.split("::=|,");
for(int i = 0; i < parts.length; i++){
parts[i] = parts[i].trim();
parts[i] = parts[i].replaceAll("\\[|]", "");
//parts[i] = parts[i].replaceAll("[ \t]+", "");
}
//Load into TreeMap
for(int i = 0; i < parts.length - 1; i+=2){
String[] temp = parts[i+1].split("\\|");
rules.put(parts[i], temp);
}
//Debug
String[] test = generate("<s>", 2);
System.out.println(test[0]);
System.out.println(test[1]);
}
/**
* Method to check if a certain non-terminal (such as <adj>
* is present in the map.
*
* Accepts a String and returns true if said non-terminal is
* in the map, and therefore a valid grammar. Returns false
* otherwise.
*
* @param symbol The string that will be checked
* @return boolean True if present, false if otherwise
*/
public boolean grammarContains(String symbol){
if(rules.keySet().toString().contains(symbol)){
return true;
}else{
return false;
}
}
/**
* Method to generate sentences based on BNF notation and
* return them as strings.
*
* @param symbol The BNF symbol to be generated
* @param times The number of sentences to be generated
* @return String The generated sentence
*/
public String[] generate(String symbol, int times){
//Array for output
String[] output = new String[times];
for(int i = 0; i < times; i++){
//Clear array for run
output[i] = "";
//Grab rules, and store in an array
lString[] grammar = rules.get(symbol);
//Generate random number and assign to var
int rand = randomNumber(grammar.length);
//Take chosen grammar and split into array
String[] rules = grammar[rand].toString().split("\\s");
//Determine if the rule is terminal or not
if(grammarContains(rules[0])){
//System.out.println("grammar has more grammars");
//Find if there is one or more conditions
if(rules.length == 1){
String[] returnString = generate(rules[0], 1);
output[i] += returnString[0];
output[i] += " ";
}else if(rules.length > 1){
for(int j = 0; j < rules.length; j++){
String[] returnString = generate(rules[j], 1);
output[i] += returnString[0];
output[i] += " ";
}
}
}else{
String[] returnArr = new String[1];
returnArr[0] = grammar[rand];;
return returnArr;
}
output[i] = output[i].trim();
}
return output;
}
/**
* Method to list all valid non-terminals for the current grammar
*
* @return String A listing of all valid non-terminals
* contained in the current grammar that
* can be used to generate words or
* sentences.
*/
String getSymbols(){
return rules.keySet().toString();
}
public int randomNumber(int max){
Random rand = new Random();
int returnVal = rand.nextInt(max);
return returnVal;
}
}
import java.io.*;
import java.util.*;
public class GrammarTest {
public static void main(String[] args) throws FileNotFoundException {
Scanner console = new Scanner(System.in);
System.out.println();
// open grammar file
Scanner input = new Scanner(new File("sentence.txt"));
// read the grammar file and construct the grammar solver
List<String> grammar = new ArrayList<String>();
while (input.hasNextLine()) {
String next = input.nextLine().trim();
if (next.length() > 0)
grammar.add(next);
}
GrammarSolver solver =
new GrammarSolver(Collections.unmodifiableList(grammar));
}
}
import java.io.*；
导入java.util.*；
公共课语法{
公共静态void main（字符串[]args）引发FileNotFoundException{
扫描仪控制台=新扫描仪（System.in）；