package com.malakana.cal;

import android.annotation.SuppressLint;

import java.util.*;

public class Yunsuan {

Yunsuan(String str1) {

EvaluateExpression(str1);

}

@SuppressLint("UseValueOf")

public static String EvaluateExpression(String str) {

char[] a;

int i = 0;

a = str.toCharArray();

Stack<Float> OPND = new Stack<Float>();

Stack<Character> OPTR = new Stack<Character>();

OPTR.push(‘=‘);

float number = 0;

int decimalnum = 1;

boolean integer = false;

boolean decimal = false;

while (true) {

if (i == str.length())

break;

if (In(a[i]) == -1) {

number = number * 10 + (a[i] - 48);

integer = true;

if (decimal)

decimalnum = decimalnum * 10;

i++;

} else if (a[i] == ‘.‘) {

if (decimal)

return "ERROR";

decimal = integer = true;

i++;

} else if (In(a[i]) > -1 && In(a[i]) < 7) {

if (In(a[i]) == 1 && (i == 0 || In(a[i - 1]) == 4))

OPND.push(new Float(0));

if (integer) {

OPND.push(new Float(number / decimalnum));

number = 0;

decimalnum = 1;

integer = decimal = false;

}

switch (Precede(In(OPTR.peek()), In(a[i]))) {

case 2:

if (OPND.empty())

return "ERROR";

float x = OPND.pop();

if (OPND.empty())

return "ERROR";

float y = OPND.pop();

char theta = OPTR.pop();

if (In(theta) == 3 && x == 0)

return "ERROR";

OPND.push(new Float(Operate(y, theta, x)));

break;

case 1:

OPTR.pop();

i++;

break;

case 0:

OPTR.push(new Character(a[i]));

i++;

break;

case -1:

return "ERROR";

}

}

}

if (OPND.empty())

return "ERROR";

else

return ("" + OPND.peek());

}

public static int In(char t) {

int i = 0;

if (t > 47 && t < 58)

return -1;

switch (t) {

case ‘+‘:

i = 0;

break;

case ‘-‘:

i = 1;

break;

case ‘*‘:

i = 2;

break;

case ‘/‘:

i = 3;

break;

case ‘(‘:

i = 4;

break;

case ‘)‘:

i = 5;

break;

case ‘=‘:

i = 6;

break;

}

return i;

}

public static int Precede(int t1, int t2) {

int relationship[][] = { { 2, 2, 0, 0, 0, 2, 2 },

{ 2, 2, 0, 0, 0, 2, 2 }, { 2, 2, 2, 2, 0, 2, 2 },

{ 2, 2, 2, 2, 0, 2, 2 }, { 0, 0, 0, 0, 0, 1, -1 },

{ 2, 2, 2, 2, -1, 2, 2 }, { 0, 0, 0, 0, 0, -1, 1 } };

return relationship[t1][t2];

}

public static float Operate(float a, char theta, float b) {

float i = 0;

switch (theta) {

case ‘+‘:

i = a + b;

break;

case ‘-‘:

i = a - b;

break;

case ‘*‘:

i = a * b;

break;

case ‘/‘:

i = a / b;

break;

}

return i;

}

public static void main(String[] args) {

new Yunsuan(null);

}

}

Java 编程处理四则运算式（包含括号）