android studio四则运算

Android Studio可以用Java语言编写四则运算程序，可以使用基本的算术运算符（+，-，*，/）和括号来实现。以下是一个简单的示例代码：

import java.util.Scanner;

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

    public static double calculate(String expression) {
        double result = 0;
        try {
            result = eval(expression);
        } catch (Exception e) {
            System.out.println("表达式不合法！");
        }
        return result;
    }

    public static double eval(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("表达式不合法！");
                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();
                    if (func.equals("sqrt")) x = Math.sqrt(x);
                    else if (func.equals("sin")) x = Math.sin(Math.toRadians(x));
                    else if (func.equals("cos")) x = Math.cos(Math.toRadians(x));
                    else if (func.equals("tan")) x = Math.tan(Math.toRadians(x));
                    else throw new RuntimeException("未知的函数：" + func);
                } else {
                    throw new RuntimeException("表达式不合法！");
                }

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

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

这个程序可以接受用户输入一个表达式，然后计算出结果。例如，如果用户输入“2+3*4”，程序将输出“14.0”。