中缀表达式 - 栈实现综合计算器

代码： 

package Algotithm.stackobject Calculator {def main(args: Array[String]): Unit = {val expression = "3+2*6-2"//创建两个栈：数栈、符号栈val numStack, operStack = new ArrayStack2(10)//定义需要的相关变量var index, num1, num2, oper, res = 0 //用于扫描var ch: Char = ' ' //每次扫描得到的char保存到chvar keepNum: String = ""//开始循环扫描入栈while (index < expression.length) {ch = expression.charAt(index)//判断是什么if (operStack.isOper(ch)) {if (operStack.isEmpty) {//如果为空直接入栈operStack.push(ch)} else {//如果不为空if (operStack.priority(ch) <= operStack.priority(operStack.peek())) {//从数栈中pop出两个数进行运算num1 = numStack.pop()num2 = numStack.pop()oper = operStack.pop()res = numStack.cal(num1, num2, oper)//把运算结果入数栈numStack.push(res)//当前符号入符号栈operStack.push(ch)} else {operStack.push(ch)}}} else {//如果是数，则直接入数栈//numStack.push(ch - 48)//1.当处理多位数时，不能发现一个数就立即入栈。因为也可能是多位数//2.在处理数时，需要像exp表达式后再看一位。如果是数就继续扫描。如果是符号再入栈//3.定义一个字符串变量，用于拼接//处理多位数keepNum += ch//如果ch已经是exp的最后一位，就直接入栈if (index == expression.length - 1) {numStack.push(keepNum.toInt)} else {//判断下一个字符是不是数字。如果是数字，就继续扫描。如果是运算符，则入栈if (operStack.isOper(expression.charAt(index + 1))) {//如果后一位时运算符，则入栈numStack.push(keepNum.toInt)//keepnum清空keepNum = ""}}}index = index + 1}while (!operStack.isEmpty) {//如果符号栈为空，则计算到最后的结果，数栈中只有一个数字num1 = numStack.pop()num2 = numStack.pop()oper = operStack.pop()res = operStack.cal(num1, num2, oper)numStack.push(res) //入栈}println(s"表达式 $expression = ${numStack.pop()}")}
}//先创建一个栈
class ArrayStack2 {private var maxSize: Int = _private var stack: Array[Int] = _private var top = -1//构造器def this(maxSize: Int) {thisthis.maxSize = maxSizestack = new Array[Int](this.maxSize)}//栈满def isFull: Boolean = {top == maxSize - 1}//栈空def isEmpty: Boolean = {top == -1}//返回当前栈顶的值def peek(): Int = {stack(top)}//入栈-pushdef push(value: Int): Unit = {if (isFull) {println(s"栈满")return}top = top + 1stack(top) = value}//出栈-popdef pop(): Int = {if (isEmpty) {throw new RuntimeException(s"栈空，没有数据")}val value = stack(top)top = top - 1value}//显示栈的情况【遍历栈】def list: Unit = {if (isEmpty) {println(s"栈空，没有数据")return}//需要从栈顶开始显示for (i <- 0 to top) {println(s"stack=${stack(top - i)}")}}//返回运算符的优先级，优先级为自定义//优先级使用数字表示。数字越大，优先级越高def priority(oper: Int): Int = {val ret = oper match {case '*' | '/' => 1case '+' | '-' => 0case _ => -1}ret}//判断是不是一个运算符def isOper(value: Char): Boolean = {value.equals('+') ||value.equals('-') ||value.equals('*') ||value.equals('/')}//计算方法def cal(num1: Int, num2: Int, oper: Int): Int = {var res: Int = 0 //用于存放计算的结果res = oper match {case '+' => num1 + num2case '-' => num2 - num1case '*' => num1 * num2case '/' => num2 / num1}res}}

总结：

Scala在模式匹配+偏函数的结合应用其灵活度太高了，，用顺手了习惯了之后会比Java简化很多。变量声明时也不用像Java一样一个变量new一次对象，可以像下面这样：