Java实现四则混合运算

使用栈来实现，可以处理运算优先级。

使用自然四则运算表达式即可，如：4+(3*(3-1)+2)/2。无需把表达式先转换为逆波兰等形式。

 

package com.joshua.cal;

import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.Stack;

public class Calculator {

	private final Stack numStack = new Stack();
	private final Stack opStack = new Stack();

	private char currentOperator;
	private char opStackTop;

	private int i;
	private String expression;

	@SuppressWarnings("rawtypes")
	public void exec(String expression) {
		try {
			clean();
			if (expression == null || expression.isEmpty()) {
				throw new IllegalArgumentException("Blank Expression!");
			}
			this.expression = expression;
			opStack.push(TERMINATE_TOKENS.START_END_MARK);
			List tokens = TOKENIZER.exec(expression
					+ TERMINATE_TOKENS.START_END_MARK);
			for (; i < tokens.size(); i++) {
				final Object token = tokens.get(i);
				if (token instanceof Double) {
					processOperand((double) token);
				} else {
					processOperator((char) token);
				}
			}
		} catch (Throwable e) {
			System.err.println(String.format(
					"Incorret Expression: %s\nError: %s", expression,
					e.getMessage()));
		}
	}

	private void processOperand(final double operand) {
		numStack.push(operand);
	}

	private void processOperator(final char currentOperator) {
		this.currentOperator = currentOperator;
		this.opStackTop = opStack.peek();
		char calMode = CALCULATE_MODE.getRule(currentOperator, opStackTop);
		switch (calMode) {
		case '>':
			processStackHigerPriorityOperator();
			break;
		case '<':
			processStackLowerPriorityOperator();
			break;
		case '=':
			processStackEqualPriorityOperator();
			break;
		default:
			break;
		}
	}

	private void processStackLowerPriorityOperator() {
		opStack.push(currentOperator);
	}

	private void processStackHigerPriorityOperator() {
		numStack.push(CALCULATE.exec(opStack.pop(), numStack.pop(),
				numStack.pop()));
		--i; // pointer back to the previous operator.
	}

	private void processStackEqualPriorityOperator() {
		if (TERMINATE_TOKENS.START_END_MARK == currentOperator) {
			System.out.println(expression + " = " + numStack.peek());
		} else if (')' == currentOperator) {
			opStack.pop();
		}
	}

	public void clean() {
		numStack.clear();
		opStack.clear();
		i = 0;
	}

	public static void main(String[] args) {
		Calculator cal = new Calculator();
		cal.exec("4+(3*(3-1)+2)/2"); // = 8
		cal.exec("4 + (-3 * ( 3 - 1 ) + 2)"); // = 0
		cal.exec("4 +-/ (-3 * ( 3 - 1 ) + 2)"); // incorrect expression!
		cal.exec("4.5+(3.2+3)/2"); // = 7.6
		cal.exec("4.5+(3.2:3)/2"); // incorrect expression!
		cal.exec("-4.5+(3.2-3)/2"); // = -4.4
	}
}

enum CALCULATE {
	INSTANCE;

	public static double exec(final char operator, final double right,
			final double left) {
		switch (operator) {
		case '+':
			return left + right;
		case '-':
			return left - right;
		case '*':
			return left * right;
		case '/':
			return left / right;
		default:
			throw new IllegalArgumentException("Unsupported operator: "
					+ operator);
		}
	}
}

enum TERMINATE_TOKENS {
	INSTANCE;

	public static final char START_END_MARK = '#';
	private static final Map TOKENs = new HashMap();

	static {
		// token, token id
		TOKENs.put('+', 0);
		TOKENs.put('-', 1);
		TOKENs.put('*', 2);
		TOKENs.put('/', 3);
		TOKENs.put('(', 4);
		TOKENs.put(')', 5);
		TOKENs.put(START_END_MARK, 6);
	}

	private static Set NEGATIVE_NUM_SENSITIVE = new HashSet();

	public static synchronized Set getNegativeNumSensitiveToken() {
		if (NEGATIVE_NUM_SENSITIVE.size() == 0) {
			NEGATIVE_NUM_SENSITIVE.addAll(TOKENs.keySet());
			NEGATIVE_NUM_SENSITIVE.remove(')');
		}
		return NEGATIVE_NUM_SENSITIVE;
	}

	public static boolean isTerminateToken(final char token) {
		Set keys = TOKENs.keySet();
		return keys.contains(token);
	}

	public static int getTokenId(final char token) {
		return TOKENs.get(token) == null ? -1 : TOKENs.get(token);
	}

	public static int getTokenSize() {
		return TOKENs.size();
	}

}

enum CALCULATE_MODE {
	INSTANCE;

	private static char[][] RULES = {
			// + - * / ( ) #
			{ '>', '>', '<', '<', '<', '>', '>' }, // +
			{ '>', '>', '<', '<', '<', '>', '>' }, // -
			{ '>', '>', '>', '>', '<', '>', '>' }, // *
			{ '>', '>', '>', '>', '<', '>', '>' }, // /
			{ '<', '<', '<', '<', '<', '=', 'o' }, // (
			{ '>', '>', '>', '>', 'o', '>', '>' }, // )
			{ '<', '<', '<', '<', '<', 'o', '=' }, // #
	};

	static {
		if (RULES.length != TERMINATE_TOKENS.getTokenSize() || RULES.length < 1
				|| RULES[0].length != TERMINATE_TOKENS.getTokenSize()) {
			throw new IllegalArgumentException("Rules matrix is incorrect!");
		}
	}

	public static char getRule(final char currentOperator, final char opStackTop) {
		try {
			return RULES[TERMINATE_TOKENS.getTokenId(opStackTop)][TERMINATE_TOKENS
					.getTokenId(currentOperator)];
		} catch (Throwable e) {
			throw new RuntimeException("No rules were defined for some token!");
		}
	}
}

enum TOKENIZER {
	INSTANCE;

	private static final StringBuilder BUFFER = new StringBuilder();

	private static String clearExpression(String expression) {
		return expression.replaceAll(" ", "");
	}

	private static Character PREVIOUS_CHAR;

	private static void clean() {
		BUFFER.delete(0, BUFFER.length());
		PREVIOUS_CHAR = null;
	}

	private static boolean processNegativeNumbers(final String exp,
			final int index) {
		char c = exp.charAt(index);
		if (('+' == c || '-' == c)
				&& (PREVIOUS_CHAR == null || TERMINATE_TOKENS
						.getNegativeNumSensitiveToken().contains(PREVIOUS_CHAR))
				&& !TERMINATE_TOKENS.isTerminateToken(exp.charAt(index + 1))) {
			BUFFER.append(c);
			return true;
		}
		return false;
	}

	@SuppressWarnings({ "unchecked", "rawtypes" })
	public static List exec(final String expression) {
		clean();
		String exp = clearExpression(expression);
		List result = new LinkedList();
		for (int i = 0; i < exp.length(); i++) {
			char c = exp.charAt(i);
			if (TERMINATE_TOKENS.isTerminateToken(c)) {
				if (processNegativeNumbers(exp, i))
					continue;
				if (BUFFER.length() > 0) {
					result.add(Double.valueOf(BUFFER.toString()));
					BUFFER.delete(0, BUFFER.length());
				}
				result.add(c);
			} else {
				BUFFER.append(c);
			}
			PREVIOUS_CHAR = c;
		}
		return Collections.unmodifiableList(result);
	}
}