用java实现计算器 实现基本数学运算、函数等功能:加、减、乘、除、阶乘、正弦、余弦和指数运算。

好的，以下是Java实现计算器的示例代码，支持加、减、乘、除、阶乘、正弦、余弦和指数运算：

import java.util.Scanner;
import java.lang.Math;

public class Calculator {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入算式：");
        String expression = sc.nextLine();
        double result = calculate(expression);
        System.out.println("计算结果为：" + result);
    }

    public static double calculate(String expression) {
        // 去掉空格
        expression = expression.replaceAll(" ", "");
        // 去掉末尾的等号
        if (expression.endsWith("=")) {
            expression = expression.substring(0, expression.length() - 1);
        }
        // 判断是否存在阶乘运算
        if (expression.contains("!")) {
            int n = Integer.parseInt(expression.substring(0, expression.length() - 1));
            double result = 1;
            for (int i = 1; i <= n; i++) {
                result *= i;
            }
            return result;
        } else {
            // 利用eval()函数计算表达式的值
            return evaluate(expression);
        }
    }

    public static double evaluate(String expression) {
        return new Object() {
            int pos = -1, ch;

            void nextChar() {
                ch = (++pos < expression.length()) ? expression.charAt(pos) : -1;
            }

            boolean eat(int charToEat) {
                while (ch == ' ') nextChar();
                if (ch == charToEat) {
                    nextChar();
                    return true;
                }
                return false;
            }

            double parse() {
                nextChar();
                double x = parseExpression();
                if (pos < expression.length()) {
                    throw new RuntimeException("Unexpected: " + (char)ch);
                }
                return x;
            }

            double parseExpression() {
                double x = parseTerm();
                for (;;) {
                    if (eat('+')) {
                        x += parseTerm();
                    } else if (eat('-')) {
                        x -= parseTerm();
                    } else {
                        return x;
                    }
                }
            }

            double parseTerm() {
                double x = parseFactor();
                for (;;) {
                    if (eat('*')) {
                        x *= parseFactor();
                    } else if (eat('/')) {
                        x /= parseFactor();
                    } else {
                        return x;
                    }
                }
            }

            double parseFactor() {
                if (eat('+')) return parseFactor();
                if (eat('-')) return -parseFactor();

                double x;
                int startPos = this.pos;
                if (eat('(')) {
                    x = parseExpression();
                    eat(')');
                } else if ((ch >= '0' && ch <= '9') || ch == '.') {
                    while ((ch >= '0' && ch <= '9') || ch == '.') nextChar();
                    x = Double.parseDouble(expression.substring(startPos, this.pos));
                } else if (ch >= 'a' && ch <= 'z') {
                    while (ch >= 'a' && ch <= 'z') nextChar();
                    String func = expression.substring(startPos, this.pos);
                    x = parseFactor();
                    switch (func) {
                        case "sin":
                            x = Math.sin(x);
                            break;
                        case "cos":
                            x = Math.cos(x);
                            break;
                        case "exp":
                            x = Math.exp(x);
                            break;
                        default:
                            throw new RuntimeException("Unknown function: " + func);
                    }
                } else {
                    throw new RuntimeException("Unexpected: " + (char)ch);
                }

                if (eat('^')) {
                    x = Math.pow(x, parseFactor());
                }

                return x;
            }
        }.parse();
    }
}

你可以尝试输入以下算式进行计算：

- 2+3
- 4-1
- 5*6
- 10/2
- 5!
- sin(30)
- cos(45)
- exp(2)