자바 수식 계산기(연산자 우선순위 고려)

ExpCalculator.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Stack;

/**
 * 피연산자 여러개 연산 가능합니다.
 * 
 * ***예제1***
 * 수식을 한 줄에 입력해주세요.
 * 23*12-37/23%12+23
 * 297.39130434782606
 * 다시하려면 Y/y를 입력하세요.
 * ***********
 * @author 강현구
 *
 */
public class ExpCalculator {

	public static void main(String[] args) {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		try {
			while(true) {
				Stack<Character> operatorStack = new Stack<>();
				Stack<Double> operandStack = new Stack<>();

				System.out.println("수식을 한 줄에 입력해주세요.");
				String inStr = br.readLine();
				String[] operands = inStr.split("[+-/*%]");

				int[] operandNums = new int[operands.length];
				boolean againFlag = false;
				for(int i=0 ; i< operands.length; i++) {
					if(operands[i].length()<1) {
						System.out.println("피연산자 수가 부족합니다.");
						againFlag = true;
						break;
					}
					try {
						operandNums[i] = Integer.parseInt(operands[i].trim());
					}catch(NumberFormatException ex) {
						System.out.println("피연산자가 숫자여야 합니다.");
						againFlag = true;
						break;
					}
				}
				if(againFlag) continue;

				if(operands.length < 2) {
					System.out.println("피연산자가 2개 이상이어야 합니다.");
					continue;
				}
				char[] operatorChars = new char[operands.length-1];
				int operatorIdx=0;
				for(char c : inStr.toCharArray()) {
					if(c=='*'||c=='/'||c=='+'||c=='-'||c=='%') {
						if(operatorIdx>=operatorChars.length) {
							System.out.println("피연산자 수가 부족합니다.");
							againFlag = true;
							break;
						}
						operatorChars[operatorIdx++] = c;
					}
				}
				if(againFlag) continue;


				//여기서부턴 연산 시작
				operandStack.push((double) operandNums[0]);
				operatorIdx = 0;
				while(operatorIdx<operatorChars.length) {
					int nextOperand = operandNums[operatorIdx+1];
					char nextOperator = operatorChars[operatorIdx];
					if(!operatorStack.empty() && getOperatorPriority(operatorStack.peek())>=getOperatorPriority(nextOperator)) {
							//스텍의 등급이 그 다음 연산자보다 같거다 크면
							//그 부분을 연산해서 결과를 다시 스텍에 저장한다.
						double opr2 = operandStack.pop();
						double opr1 = operandStack.pop();
							operandStack.push(calculate(opr1, opr2, operatorStack.pop()));
					}else {
						//스택에 넣기
						operandStack.push((double)nextOperand);
						operatorStack.push(nextOperator);
						operatorIdx++;
					}
				}
				while(!operatorStack.empty()) {
					double opr2 = operandStack.pop();
					double opr1 = operandStack.pop();
					operandStack.push(calculate(opr1, opr2, operatorStack.pop()));
				}

				System.out.println("="+operandStack.peek());
				System.out.println("다시하려면 Y/y를 입력하세요.");
				String respond = br.readLine().trim();
				if(respond.length()!=1 || (respond.charAt(0)!='Y' && respond.charAt(0)!='y')) break;
			}
			br.close();
		} catch (IOException e) {
			e.printStackTrace();
			System.out.println("IOException이 발생하였습니다.");
		}
	}
	//연산자가 아닐순 없지만 아니면 -1.
	private static int getOperatorPriority(char c) {
		switch(c) {
		case '*':
		case '/':
		case '%':
			return 2;
		case '+':
		case '-':
			return 1;
		}
		return -1;
	}
	
	private static double calculate(double opr1, double opr2, char c) {
		switch(c) {
		case '*':
			return opr1*opr2;
		case '/':
			return opr1/opr2;
		case '%':
			return opr1%opr2;
		case '+':
			return opr1+opr2;
		case '-':
			return opr1-opr2;
		}
		return -1;
	}
}