2

public boolean checking(){ //Конечный автомат для проверки правильности введенного выражения
        int numOfLexem = 0;
        int balance = 0;
        for(Lexem l : RPN){
            numOfLexem++;
            switch (currentState) {

            case BEGIN:
                System.out.println("Balance: " + balance + " " + currentState + " " + l.type);
                switch(l.type){
                case LEFT:
                    currentState = State.BEGIN;
                    balance++;
                    break;
                case RIGHT:
                case UNARY:
                    currentState = State.ERROR;
                    break;
                case OPERATION:
                    currentState = State.OPERATION;
                    l.type = LexemType.UNARY;
                    break;
                case FUNCTION:
                    currentState = State.FUNCTION;
                    break;
                case NUMBER:
                case CONSTANT:
                    currentState = State.OPERAND;
                    break;
                }
                break;

            case FUNCTION:
                System.out.println("Balance: " + balance + " " + currentState + " " + l.type);
                switch(l.type){
                case LEFT:
                    balance++;
                    currentState = State.BEGIN;
                    break;
                case RIGHT:
                case UNARY:
                case OPERATION:
                case FUNCTION:
                case NUMBER:
                case CONSTANT:
                    currentState = State.ERROR;
                    break;
                }
                break;

            case OPERATION:
                System.out.println("Balance: " + balance + " " + currentState + " " + l.type);
                switch (l.type) {
                case LEFT:
                    balance++;
                    currentState = State.BEGIN;
                    break;
                case RIGHT:
                case UNARY:
                case OPERATION:
                    currentState = State.ERROR;
                    break;
                case FUNCTION:
                    currentState = State.FUNCTION;
                    break;
                case NUMBER:
                case CONSTANT:
                    currentState = State.OPERAND;
                    break;
                }
                break;

            case OPERAND:
                System.out.println("Balance: " + balance + " " + currentState + " " + l.type);
                switch (l.type){
                case LEFT:
                case NUMBER:
                case CONSTANT:
                case FUNCTION:
                case UNARY:
                    currentState = State.ERROR;
                    break;
                case OPERATION:
                    currentState = State.OPERATION;
                    break;
                case RIGHT:
                    balance--;
                    currentState = State.OPERAND;
                }
                break;

            default:
                break;
            }
            if(currentState == State.ERROR){
                System.out.println("Incorrect syntax at lexem (num:" + numOfLexem + ") :  " + l);
                for(Lexem lp : RPN){
                    if(lp == l)
                        System.out.print(" `" + lp.toString(false) + "` ");
                    else
                        System.out.print(lp.toString(false));
                }
                return false;
            }
            if(balance!=0){
                System.out.println("Check brackets!" + numOfLexem);
                return false;
            }
        }
        return true;
    }