关于#java#的问题，如何解决？

就是我想弄个代码，求命题的真值表，但是不知道为啥，一直就是有异常，关于栈的

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package 大作业;

import java.util.*;

public class LiSanMath {
    public static void main(String[] args){
        System.out.println("输入命题公式：");
        Scanner sc=new Scanner(System.in);
        String proposition=sc.nextLine();
        CreateTable(proposition);
    }
    public static void CreateTable(String proposition){
        boolean[][] table1=table(proposition);
        boolean[] result=Calculate(proposition);
        HashSet<String> hs=Bianyuan(proposition);
        for(String s:hs){
            System.out.print(s+"\t");
        }
        System.out.print(proposition);
        System.out.print("\n");
        for (int i = 0; i < (int)Math.pow(2,count(proposition)); i++) {
            for (int j = 0; j < count(proposition); j++) {
                if(table1[i][j]==false) System.out.print("0");
                else System.out.print("1");
                System.out.print("\t");
            }
            if(result[i]==false) System.out.print("0");
            else System.out.print("1");
            System.out.print("\n");
        }
    }
    public static int count(String proposition){
        int count = 0;
        for (int i = 0; i < proposition.length(); i++) {
            char ch=proposition.charAt(i);
            if(ch<='Z'&&ch>='A')count++;
        }
        return count;
    }
    public static HashSet<String> Bianyuan(String proposition){
        HashSet<String> hs=new HashSet<>();
        for (int i = 0; i < proposition.length(); i++) {
            char ch=proposition.charAt(i);
            if(ch<='Z'&&ch>='A')hs.add(String.valueOf(ch));
        }
        return hs;
    }

    public static boolean[][] table(String proposition){
        int col=count(proposition);
        int row= (int) Math.pow(2,col);
        boolean[][] table=new boolean[row][col];
        for (int i = 0; i < row; i++) {
            int[] value=new int[col];
            for (int j = col-1; j>=0; j--) {
                int x=(int)Math.pow(2,j);
                value[col-j-1]=i/x%2;
            }
            for (int j = 0; j < col; j++) {
                table[i][j]=value[j]==1;
            }
        }
        return table;
    }
    public static boolean[] Calculate(String proposition){
        //运算符的优先级
            HashMap<String,Integer> ch=new HashMap<>();
            ch.put("&",1);
            ch.put("|",1);
            ch.put("!",0);
            ch.put("-",2);
            ch.put("+",3);
            ch.put("@",1000);
        boolean[] result=new boolean[(int) Math.pow(2,count(proposition))];
        boolean[][] table=table(proposition);
        int index_1=0;
        while(index_1<(int)Math.pow(2,(count(proposition)))){
            boolean[] table_1=new boolean[count(proposition)];
            HashMap<String,Boolean> hm=new HashMap<>();
            HashSet<String> bianyuan=Bianyuan(proposition);
            for (int i = 0; i < count(proposition); i++) {
                table_1[i]=table[index_1][i];
            }
            int x=0;
            for(String s:bianyuan){
                hm.put(s,table_1[x]);
                x++;
            }
            Stack<Boolean> stack_1=new Stack<>();
            Stack<String> stack_2=new Stack<>();
            stack_2.push("@");
            stack_1.push(false);
            int index_2=0;
            while (index_2<proposition.length()){
                char cha=proposition.charAt(index_2);
                if(cha>='A'&&cha<='Z'){
                    stack_1.push(hm.get(cha));
                }
                else {
                    if(stack_2.empty()==true)stack_2.push(String.valueOf(cha));
                    else {
                        if(cha=='('){
                            stack_2.push(String.valueOf(cha));
                        }
                        else if(cha!=')'&&cha!='('){
                            String s1=stack_2.peek();
                            String s2= String.valueOf(cha);
                            if(ch.get(s1)>ch.get(s2)){
                                stack_2.push(s2);
                            }
                            else {
                                boolean b1=stack_1.pop();
                                boolean b2=stack_1.pop();
                                boolean b3=Calcuate_1(s2,b1,b2);
                                if(s1.equals("!")){
                                    stack_1.push(b1);
                                    stack_1.push(b3);
                                }
                                else stack_1.push(b3);
                            }
                        }
                        else if (cha==')') {
                            while (stack_2.peek()!="("){
                                boolean b1=stack_1.pop();
                                boolean b2=stack_1.pop();
                                String s1=stack_2.pop();
                                boolean b3=Calcuate_1(s1,b1,b2);
                                if(s1.equals("!")){
                                    stack_1.push(b1);
                                    stack_1.push(b3);
                                }
                                else stack_1.push(b3);
                                if (stack_2.peek()=="(")stack_2.pop();
                            }
                        }
                    }
                }
                index_2++;
            }
            while (stack_2.peek()!="@"){
                boolean b1=stack_1.pop();
                boolean b2=stack_1.pop();
                String s1=stack_2.pop();
                boolean b3=Calcuate_1(s1,b1,b2);
                if(s1.equals("!")==true){
                    stack_1.push(b1);
                    stack_1.push(b3);
                }
                else stack_1.push(b3);
            }
            result[index_1]=stack_1.pop();
            index_1++;
        }
        return result;
    }
    public static boolean Calcuate_1(String fuhao,boolean b1,boolean b2){
        boolean result = false;
        switch (fuhao){
            case "&":result=b1&&b2;break;
            case "|":result=b1||b2;break;
            case "-":{
                if(b1==true&&b2==false) result=false;
                else result=true;
            }break;
            case "+":{
                if (b1==b2)result=true;
                else result=false;
            }break;
            case "!":result=!b2;
        }
        return result;
    }
}

ch里没有左括号和右括号，109行 if(ch.get(s1)>ch.get(s2)) 当s1为"("时，ch.get(s1) 为null ，null不能用> 比较大小