java编写简单的语法分析预测程序

编译原理课程中，编了一个简单的语法分析预测程序，这个程序时根据固定的文法得到预测分析表，然后编写程序来判断表达式是否会正确推到出来。

前提是程序没有左递归符合LL(1)文法：

文法如下：

E→TE'

E’ →+TE'|ε

T→FT'

T’ →*FT'|ε

 F→(E)|i

为了程序便于编写将E'替换为e,T'替换为t

(2)FIRST集

FIRST(E)={(,i}; 

FIRST(E’)={+, ε};

FIRST(T)={(,i};

FIRST(T’)={ *, ε};

FIRST(F)={(,i};

(3)FALLOW集

FOLLOW(E)={),#};

FOLLOW(E’)={),#};

FOLLOW(T)={+,),#};

FOLLOW(T’)={+,),#};

FOLLOW(F)={*,+,),#};

(4)预测分析表

	i	+	*	(	)	#
E	E->TE’			E->TE’
E’		E’->+TE’			E’->ε	E’->ε
T	T->FT’			T->FT’
T’		T’->ε	T’->*FT’		T’->ε	T’->ε
F	F->i			F->(E)

 一、Stack.java

public class Stack {
    private char s[];
    private int top;
    private int base;
    private final int MAX = 200;
    /**
     * 
    * <p>Title: </p>
    * <p>Description: 初始化栈</p>
     */
    public Stack() {
        initStack();
    }
    private void initStack() {
        s = new char[MAX];
        base = 0;
        top = 0;        
    }
    public boolean isEmpty() {
        if(top == base) {
            return true;
        }else {
            return false;
        }
    }
    /**
     * 
    * <p>Title: getTop</p>
    * <p>Description: 获取栈顶元素</p>
    * @return 返回栈顶元素
     */
    public char getTop() {
        return s[top-1];
    }
    /**
     * 
    * <p>Title: push</p>
    * <p>Description: 进栈方法</p>
    * @param str 进栈的字符
     */
    public void push(String str) {
        for (int i = str.length() - 1; i >= 0; i--) {
            s[top++] = str.charAt(i);
        }
    }
    /**
     * 
    * <p>Title: clear</p>
    * <p>Description: 清空栈</p>
     */
    public void clear() {
        top = base;
    }
    
    /**
     * 
    * <p>Title: pop</p>
    * <p>Description: 出栈</p>
    * @return 栈顶元素出栈并返回出栈的元素
     */
    public char pop() {
        return s[--top];
    }
    /**
     * 
    * <p>Title: size</p>
    * <p>Description: 返回栈中元素个数</p>
    * @return 栈中元素个数
     */
    public int size() {
        return top;
    }
    /**
     * 打印栈里面的元素
     */
    public String toString() {
        StringBuffer tempStack = new StringBuffer();
        for (int i = 0; i < top; i++) {
            tempStack.append(s[i]);
        }
        return tempStack.toString();
    }
}

二、GrammarAnalyze.java

package grammarAnalyze;

public class GrapparAnalyze {
	//分析表将E'替换为e,T'替换t
	private String tab[][] = { 
		{ "$", "i",  "+",   "*",  "(",   ")", "#" },
		{ "E", "Te", "$",   "$",  "Te", "$",  "$" },
		{ "e", "$", "+Te", "$",   "$",  "ε",  "ε" },
		{ "T", "Ft", "$",   "$",  "Ft","$",  "$" },
		{ "t", "$",  "ε",   "*Ft", "$", "ε",  "ε" },
		{ "F",  "i",  "$",   "$",  "(E)","$", "$" } };
	private String input;  //input中存放输入的表达式
	private StringBuffer tempBuffer;    //存放要输出的字符串
	private int ptr, row, col, step; //指针，预测表中的行，列，当前步骤
	private boolean symbol;
	private Stack stack;
	public GrapparAnalyze(){
		stack = new Stack();
		tempBuffer = new StringBuffer();
		symbol=true;
		input="";
		stack.clear();
		stack.push("#");
		row=1;
		ptr=0;
		step=1;
	}
	public int column(char c) {  //判断预测表中的列
		switch (c) {
		case 'i':
			return 1;
		case '+':
			return 2;
		case '*':
			return 3;
		case '(':
			return 4;
		case ')':
			return 5;
		case '#':
			return 6;
		default:
			return -1;
		}
	}
	public int line(char c) { //判定预测表中的行
		switch (c) {
		case 'E':
			return 1;
		case 'e':
			return 2;
		case 'T':
			return 3;
		case 't':
			return 4;
		case 'F':
			return 5;
		default:
			return -1;
		}
	}
	public void show(String str) {
		tempBuffer.append(String.format("%-7d%-14s%-20s%-20s
", 
				step, filter(stack.toString()), filter(input.substring(ptr)), filter(str)));
	     step++;
	}
	public void analyse() {
		stack.push(tab[row][0]);   //预测表中的第一个元素‘E’
		show("初始化");
		String tmp;
		char ctmp;   //栈顶元素
		while (!(input.charAt(ptr) == '#' && stack.getTop() == '#')) {
			ctmp = stack.getTop();//获取栈顶的元素
			if (input.charAt(ptr) == ctmp) { //与栈顶元素比较
				stack.pop();
				ptr++;
				show("" + ctmp + "匹配");
				continue;
			}
			//判断ptr位置的终结符所在预测表的列位置
			col = column(input.charAt(ptr));
			if (col == -1) {
				symbol = false;
				show("未定义的字符");
				ptr++;
				break;
			}
			//判断栈顶位置所在预测表的行位置
			row = line(ctmp);
			if (row == -1) {
				symbol = false;
				show("出错");
				stack.pop();
				if (input.charAt(ptr) != '#') {
					ptr++;
				}
				continue;
			}
			tmp = tab[row][col];
			if (tmp.charAt(0) == '$') {
				symbol = false;
				show("出错");
				stack.pop();
				if (input.charAt(ptr) != '#') {
					ptr++;
				}
			} else if (tmp.charAt(0) == 'ε') {
				stack.pop();
				show("" + ctmp + "->" + 'ε');
			} else {
				stack.pop();
				stack.push(tmp);
				show("" + ctmp + "->" + tmp);
			}
		}
	}
　　　　　　//过滤方法将打印的字符串中e和t替换为E'和T'
	public String filter(String src) {
		if(src.contains("e") || src.contains("t")) {
			StringBuffer result = new StringBuffer();
			char item;
			for(int i = 0;i < src.length(); i++) {
				item = src.charAt(i);
				if(item == 'e') {
					result.append("E'");
					continue;
				}else if(item == 't') {
					result.append("T'");
					continue;
				}
				result.append(item);
			}
			return result.toString();
		}else {
			return src;
		}
	}
	public String work(String inputExpression) { 
		input = inputExpression + '#';
		symbol = true;
		tempBuffer.append(String.format("%-8s%-20s%-20s%-20s
",
				"步骤","分析栈","剩余输入栈","所用产生式"));
		analyse();
		if (symbol) {
			tempBuffer.append("
是正确的符号串
");
			return tempBuffer.toString();
		} else {
			tempBuffer.append("
不是正确的符号串
");
			return tempBuffer.toString();
		}
			
	}

	public StringBuffer getTempBuffer() {
		return tempBuffer;
	}
	public void setTempBuffer(StringBuffer tempBuffer) {
		this.tempBuffer = tempBuffer;
	}
	public Stack getStack() {
		return stack;
	}
	public void setStack(Stack stack) {
		this.stack = stack;
	}
	public String[][] getTab() {
		return tab;
	}
	public void setTab(String[][] tab) {
		this.tab = tab;
	}
	public String getInput() {
		return input;
	}
	public void setInput(String ns) {
		this.input = ns;
	}
	public int getPtr() {
		return ptr;
	}
	public void setPtr(int ptr) {
		this.ptr = ptr;
	}
	public int getRow() {
		return row;
	}
	public void setRow(int row) {
		this.row = row;
	}
	public int getCol() {
		return col;
	}
	public void setCol(int col) {
		this.col = col;
	}
	public int getStep() {
		return step;
	}
	public void setStep(int step) {
		this.step = step;
	}
	public boolean isBoo() {
		return symbol;
	}
	public void setBoo(boolean boo) {
		this.symbol = boo;
	}

}

　　三、主程序GrammarMain.java

package grammarAnalyze;

import java.util.Scanner;

public class GrammarMain {
	public static void main(String[] args){
		boolean isContinue = true;
		while(isContinue) {
			GrapparAnalyze analyze = new GrapparAnalyze();
			Scanner scan = new Scanner(System.in);
			System.out.println("请输入你要翻译的表达式：");
			String inputExpression = scan.nextLine();
			String srcdata = inputExpression.trim();
			if("".equals(srcdata) || srcdata == null) {
				System.out.println("输入表达式为空，请重新输入");
			}else {
				String result = analyze.work(srcdata);
				System.out.println(result);
				System.out.println("是否继续？y/n");
				String yn = scan.nextLine();
				if("no".equals(yn) || "n".equals(yn)) {
					isContinue = false;
				}
			}
		}

	}
	
}

　　四、测试运行