简易版的计算器

就不多说了，很简单，直接上代码。（注意在整个运算中没有涉及浮点数）

public class StackTest3 {private static Stack s1=new Stack(); //符号栈private static Stack s2=new Stack(); //数字栈public static void main(String[] args) {Scanner in=new Scanner(System.in);String s=in.next();int by=0;for (int i = 0; i < s.length(); i++) {char ch=s.charAt(i); //当前字符int flag = priority(ch);if(s2.isEmpty()==true&&(flag==1||flag==0)) {if(flag==1) {System.out.println("错误");return;}s2.push(0);}if(flag==-1) {if(by>0) {Integer pop1 = s2.pop();StringBuffer v1=new StringBuffer(String.valueOf(pop1));v1.append(String.valueOf(ch));int num = Integer.parseInt(v1.toString());s2.push(num);by++;}else {s2.push(Integer.valueOf(String.valueOf(ch)));by++;}}else if(flag==1) {by=0;if(s1.isEmpty()==true||s1.peek()=='(') {s1.push(ch);}else {Character peek = s1.peek();if(priority(peek)==1) {//当前的优先级小于或等于栈顶的优先级Integer pop1 = s2.pop(); //数据栈中的第一个 元素Integer pop2 = s2.pop(); //数据栈中的第二个元素Character pop = s1.pop(); //字符栈中的栈顶元素Integer num = yunsuan(pop2,pop1,pop);if(num==null) {System.out.println("错误");return;}s1.push(ch);s2.push(num);}else if(priority(peek)==0) {s1.push(ch);}}}else if(flag==0) { //当前是 + 或-by=0;if(s1.isEmpty()==true||s1.peek()=='(') {s1.push(ch);}else {Character peek = s1.peek();if(priority(peek)==1||priority(peek)==0) {//当前的优先级小于或等于栈顶的优先级Integer pop1 = s2.pop(); //数据栈中的第一个 元素Integer pop2 = s2.pop(); //数据栈中的第二个元素Character pop = s1.pop(); //字符栈中的栈顶元素Integer num = yunsuan(pop2,pop1,pop);if(num==null) {System.out.println("错误");return;}s1.push(ch);s2.push(num);}}}else if(flag==2) {//左括号by=0;s1.push(ch);}else if(flag==3) {//右括号by=0;while(s1.peek()!='(') {Integer pop1 = s2.pop(); //数据栈中的第一个 元素Integer pop2 = s2.pop(); //数据栈中的第二个元素Character pop = s1.pop(); //字符栈中的栈顶元素Integer num = yunsuan(pop2,pop1,pop);if(num==null) {System.out.println("错误");return;}s2.push(num);}s1.pop();}}while(s1.isEmpty()!=true) {Integer pop1 = s2.pop();Integer pop2 = s2.pop();Character pop = s1.pop();Integer num = yunsuan(pop2,pop1,pop);if(num==null) {System.out.println("错误");return;}s2.push(num);}System.out.println(s2.peek());}public static int priority(char oper) {if(oper=='*'||oper=='/') {return 1;}else if(oper=='+'||oper=='-') {return 0;}else if(oper=='(') {return 2;}else if(oper==')') {return 3;}else {return -1;}}public static Integer yunsuan(Integer x,Integer y,Character pop) {if(pop=='+') {return x+y;}else if(pop=='-') {return x-y;}else if(pop=='*') {return x*y;}else if(pop=='/') {if(y==0) {return null;}return x/y;}return null;}}