(学习java)顺序栈实现逆波兰表达式

import java.util.Arrays;import java.util.Scanner;//10-21逆波兰表达式计算器public class RPN {public static void main(String[] args) {Scanner sc = new Scanner(System.in);// 将输入的字符串转换成一个字符数组System.out.println("请输入逆波兰表达式: ");char[] s = sc.nextLine().toCharArray();ArrStack arr = rpn(s);arr.listStack();}//逆波兰表达式public static ArrStack rpn(char[] s) {ArrStack as = new ArrStack();double num = 0;// 定义空字符串存入字符String arr = "";double a = 0;double b = 0;double result = 0;for (int i = 0; i < s.length; i++) {// 如果是数字字符,将其依次存入字符串中,则在遇到空格后,将字符串转换成double类型推入栈中if (isNumber(s[i]) || s[i] == '.') {arr = arr + s[i];} else if (s[i] == ' ') {// 遇到空格,将数据取出转成double类型推入栈中if(arr == ""){continue;}else{num = Double.valueOf(arr);as.stackPush(num);// 字符串置空arr = "";}}else{//遇到运算符字符,弹出栈顶前两个数进行运算后再压入栈中switch(s[i]){case '+':a = as.stackPop();b = as.stackPop();result = b + a;as.stackPush(result);break;case '-':a = as.stackPop();b = as.stackPop();result = b - a;as.stackPush(result);break;case '*':a = as.stackPop();b = as.stackPop();result = b * a;as.stackPush(result);break;case '/':a = as.stackPop();b = as.stackPop();if(a == 0){System.out.println("除数不能为0!");break;}result = b / a;as.stackPush(result);break;}}}return as;}// 判断字符是否为数字public static boolean isNumber(char c) {if (c >= 48 && c <= 57) {return true;}return false;}// 创建顺序栈public static class ArrStack {// 定义数组保存元素private Object[] elementData;// 定义栈的当前长度private int size;// 定义栈的当前容量private int capacity;// 定义栈顶public int top;// 初始化,默认建立一个容量为50的数组public ArrStack() {elementData = new Object[50];capacity = 50;}// 初始化,自定义容量数组public ArrStack(int n) {elementData = new Object[n];capacity = n;}// 入栈public <T> void stackPush(T data) {// 如果容量满了,则新建一个数组扩充容量if (size >= capacity) {int newLength = (capacity * 3 / 2) + 1;elementData = Arrays.copyOf(elementData, newLength);capacity = newLength;}elementData[top] = data;top++;size++;}// 出栈public <T> T stackPop() {if (size == 0) {System.out.println("当前为空栈");return null;} else {T data = (T) this.elementData[top - 1];top--;size--;return data;}}// 遍历栈public void listStack() {if (size == 0) {System.out.println("空栈");} else if (size == 1) {System.out.println(elementData[top-1]);System.out.println("栈的长度" + size);} else {for (int i = 0; i < size; i++) {System.out.print(elementData[i] + " ");}System.out.println("栈的长度" + size);}}// 返回当前容量public void capacity() {System.out.println("当前最大容量" + capacity);}}}