JAVA实现LR分析器
目的：熟练掌握自下而上的语法分析方法，并能用程序实现。
要求：
1. 使用如下文法：
E -> E+T | T
T-> T*F | F
F -> (E) | id
2. 对于任意给定的输入串（词法记号流）进行语法分析，要求采用LR分析器来完成。手工构造LR分析表，利用移进-归约分析算法（P71 图3.12）输出（P72 表3.8）对应的动作部分。如：
输入：id*+id/(id+id)#
输出：移进
按 F->id归约
移进
error
……
3. 要有一定的错误处理功能。即对错误能提示，并且能在一定程度上忽略尽量少的记号来进行接下来的分析。
例如：
从状态0开始的记号流为：bm
将b移进之后，栈里的情况应该为： 0 b 2
此时查表发现 action[2,m]=error
输出打印：error
把A和状态1相继压入栈，用户指针后移到FOLLOW(A)对应的元素继续分析。
扩展：
1.利用P94页的表3.13的方式将错误进行分类提示，即给出具体的出错信息。
2. 在已有文法的基础上再加上减法“-”和除法“/”对应的产生式构成最终的文法。从而使得记号流可以处理带括号的加、减、乘、除四则运算。
这个题就是要利用LR的动作转移表实现LR 分析器~代码在下面~
import java.util.Scanner;
import java.util.Stack;
public class Test {
private static String Str = null; // 输入串
private static String Sub = null; //输入串的待处理部分
private static boolean acc = false;// 是否已处理完输入串
private static boolean bResult = false;// 是否出错
// Goto表，即每个状态遇见非终结符时的动作
private static int[][] Goto = new int[][] { { 1, 2, 3 }, { 0, 0, 0 }, { 0, 0, 0 }, { 0, 0, 0 }, { 8, 2, 3 },
{ 0, 0, 0 }, { 0, 9, 3 }, { 0, 0, 10 }, { 0, 0, 0 }, { 0, 0, 0 }, { 0, 0, 0 }, { 0, 0, 0 } };
private static Stack stack = new Stack();// 状态栈，栈中元素都是String类型
/**
*
* @param state 状态
* @param fzjf 遇见的非终结符
* fzjf == 'E'代表是Goto表的第一列
* fzjf == 'T'代表是Goto表的第二列
* fzjf == 'F'代表是Goto表的第三列
*/
public static void Gto(int state, char fzjf) {
int i = -1;
if (fzjf == 'E')
i = 0;
if (fzjf == 'T')
i = 1;
if (fzjf == 'F')
i = 2;
stack.push(fzjf + ""); //将非终结符压入栈中，字符+空串转化为字符串
stack.push(Goto[state][i] + "");//将Goto表中对应的状态压入栈中
}
/**
* e1代表缺少运算对象 将“id”压入栈中，随即将相应的状态压入栈中
*
*/
public static void e1() {
System.out.println("缺少运算对象");
stack.push("id");
stack.push(String.valueOf(3));
// bResult = true;
//若该行不注释掉，程序遇到输入错误就会立即停止 ；若注释掉，程序不会立即停止，而是会恢复错误
}
public static void e3() {
System.out.println("缺少算符");
stack.push("+");
stack.push("" + 6);
// bResult = true;
}
public static void e3_() {
System.out.println("缺少算符");
stack.push("*");
stack.push("" + 7);
// bResult = true;
}
public static void e2() {
System.out.println("不匹配的右括号");
Sub = Sub.substring(1, Sub.length());
// bResult = true;
}
public static void e4() {
System.out.println("缺少右括号");
stack.push("");
stack.push(11 + "");
// bResult = true;
}
public static void e5() {
System.out.println("算符错误");
stack.push("+");
stack.push(6 + "");
Sub = Sub.substring(1, Sub.length());
// bResult = true;
}
public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.println("请输入串：");
Scanner in = new Scanner(System.in);
Str = in.nextLine();
Sub = Str; //初始时Sub = Str
in.close();
int y;
boolean flag = false;
// 0状态先进栈
stack.push(String.valueOf(0));
while (!bResult && acc == false) {
switch (stack.peek().charAt(0)) {
case '0':
if (Sub.substring(0, 2).equals("id")) {
stack.push("id");
stack.push("" + 5);
Sub = Sub.substring(2, Sub.length());
System.out.println("移进");
} else if (Sub.substring(0, 1).equals("(")) {
stack.push("(");
stack.push("" + 4);
Sub = Sub.substring(1, Sub.length());
System.out.println("移进");
} else {
e1();
}
break;
case '1':
if ("1".equals(stack.peek())) {
if (Sub.substring(0, 1).equals("+")) {
stack.push("id");
stack.push("" + 6);
Sub = Sub.substring(1, Sub.length());
System.out.println("移进");
} else if (Sub.substring(0, 1).equals("#")) {
acc = true;
System.out.println("接受");
} else {
e3();
}
break;
} else if (stack.peek().charAt(1) == '0') {
if (Sub.substring(0, 1).equals("+")) {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'T');
System.out.println("按T->T*F归约");
} else if (Sub.substring(0, 1).equals(")")) {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'T');
System.out.println("按T->T*F归约");
} else if (Sub.substring(0, 1).equals("#")) {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'T');
System.out.println("按T->T*F归约");
} else if (Sub.substring(0, 1).equals("*")) {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'T');
System.out.println("按T->T*F归约");
} else {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'T');
System.out.println("按T->T*F归约");
}
break;
} else {
if (Sub.substring(0, 1).equals("+")) {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'F');
System.out.println("按F->(E)归约");
} else if (Sub.substring(0, 1).equals(")")) {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'F');
System.out.println("按F->(E)归约");
} else if (Sub.substring(0, 1).equals("#")) {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'F');
System.out.println("按F->(E)归约");
} else if (Sub.substring(0, 1).equals("*")) {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'F');
System.out.println("按F->(E)归约");
} else {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'F');
System.out.println("按F->(E)归约");
}
break;
}
case '2':
if (Sub.substring(0, 1).equals("*")) {
stack.push("*");
stack.push("" + 7);
Sub = Sub.substring(1, Sub.length());
System.out.println("移进");
} else if (Sub.substring(0, 1).equals("+")) {
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'E');
System.out.println("按E->T归约");
} else if (Sub.substring(0, 1).equals(")")) {
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'E');
System.out.println("按E->T归约");
} else if (Sub.substring(0, 1).equals("#")) {
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'E');
System.out.println("按E->T归约");
} else {
e3_();
}
break;
case '3':
if (Sub.substring(0, 1).equals("+")) {
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'T');
System.out.println("按T->F归约");
} else if (Sub.substring(0, 1).equals(")")) {
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'T');
System.out.println("按T->F归约");
} else if (Sub.substring(0, 1).equals("#")) {
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'T');
System.out.println("按T->F归约");
} else if (Sub.substring(0, 1).equals("*")) {
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'T');
System.out.println("按T->F归约");
} else {
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'T');
System.out.println("按T->F归约");
}
break;
case '4':
if (Sub.substring(0, 2).equals("id")) {
stack.push("id");
stack.push("" + 5);
Sub = Sub.substring(2, Sub.length());
System.out.println("移进");
} else if (Sub.substring(0, 1).equals("(")) {
stack.push("(");
stack.push("" + 4);
Sub = Sub.substring(1, Sub.length());
System.out.println("移进");
} else if (Sub.substring(0, 1).equals(")")) {
e2();
} else
e1();
break;
case '5':
if (Sub.substring(0, 1).equals("+")) {
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'F');
System.out.println("按F->id归约");
} else if (Sub.substring(0, 1).equals(")")) {
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'F');
System.out.println("按F->id归约");
} else if (Sub.substring(0, 1).equals("#")) {
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'F');
System.out.println("按F->id归约");
} else if (Sub.substring(0, 1).equals("*")) {
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'F');
System.out.println("按F->id归约");
} else {
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'F');
System.out.println("按F->id归约");
}
break;
case '6':
if (Sub.length() > 1) {
if (Sub.substring(0, 1).equals("(")) {
stack.push("(");
stack.push("" + 4);
Sub = Sub.substring(1, Sub.length());
System.out.println("移进");
} else if (Sub.substring(0, 2).equals("id")) {
stack.push("id");
stack.push("" + 5);
Sub = Sub.substring(2, Sub.length());
System.out.println("移进");
} else if (Sub.substring(0, 1).equals(")")) {
e2();
}
} else
e1();
break;
case '7':
if (Sub.substring(0, 2).equals("id")) {
stack.push("id");
stack.push("" + 5);
Sub = Sub.substring(2, Sub.length());
System.out.println("移进");
} else if (Sub.substring(0, 1).equals("(")) {
stack.push("(");
stack.push("" + 4);
Sub = Sub.substring(1, Sub.length());
System.out.println("移进");
} else if (Sub.substring(0, 1).equals("(")) {
stack.push("(");
stack.push("" + 4);
Sub = Sub.substring(1, Sub.length());
System.out.println("移进");
} else if (Sub.substring(0, 1).equals(")")) {
e2();
} else
e1();
break;
case '8':
if (Sub.substring(0, 1).equals("+")) {
stack.push("+");
stack.push("" + 6);
Sub = Sub.substring(1, Sub.length());
System.out.println("移进");
} else if (Sub.substring(0, 1).equals(")")) {
stack.push(")");
stack.push("" + 11);
Sub = Sub.substring(1, Sub.length());
System.out.println("移进");
} else if (Sub.substring(0, 1).equals("#")) {
e4();
} else if (Sub.substring(0, 1).equals("*")) {
e5();
} else
e3();
break;
case '9':
if (Sub.substring(0, 1).equals("*")) {
stack.push("*");
stack.push("" + 7);
Sub = Sub.substring(1, Sub.length());
System.out.println("移进");
} else if (Sub.substring(0, 1).equals("+")) {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'E');
System.out.println("按E->E+T归约");
} else if (Sub.substring(0, 1).equals(")")) {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'E');
System.out.println("按E->E+T归约");
} else if (Sub.substring(0, 1).equals("#")) {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'E');
System.out.println("按E->E+T归约");
} else {
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
stack.pop();
Gto((int) stack.peek().charAt(0) - (int) '0', 'E');
System.out.println("按E->E+T归约");
}
break;
}
}
if (acc)
{
System.out.println("匹配成功");
}
}
}
我使用了短语级的错误恢复策略，此时LR分析表已经改为
程序运行效果：
1、正常输入的情况：
2、输入有错误：
可以看出提示了缺少算符，并且恢复了错误，使得语法分析能够正常执行结束
缺少右括号
缺少运算对象~
按理说还可以用粗略的恢复错误方法，不过我没有实现，欢迎大家补充~