文章目錄

• • 數組模擬棧類
  • 中綴表達式計算器類（測試類）

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數組模擬棧類

主要實現棧的一些基本功能，以及在該場景下的功能。

//先創建一個棧 class AStack {private int maxSize; //棧的大小private int[] stack; //數組模擬棧private int top = -1; //棧頂，初始化-1//構造器public AStack(int maxSize) {this.maxSize = maxSize;stack = new int[maxSize];}//棧滿public boolean isFull(){return top == maxSize - 1;}//棧空public boolean isEmpty(){return top == -1;}//入棧public void push(int value){if (isFull()){System.out.println("棧滿，入棧失敗！");return;}top++;stack[top] = value;}//出棧public int pop(){if (isEmpty()){throw new RuntimeException("棧空，出棧失敗！");}return stack[top--]; //先得到stack[top]，然后top--}//返回棧頂值public int peek(){return stack[top];}//遍歷（從棧頂向下）public void show(){if (isEmpty()){System.out.println("棧空！");return;}for (int i = top; i >= 0; i--) {System.out.printf("stack[%d] = %d\n",i,stack[i]);}}//返回運算符優先級（約定數值越大，優先級越高）public int priority(char operator){if (operator == '*' || operator == '/'){return 1;}else if (operator == '+' || operator == '-'){return 0;}else return -1; //假設只有加減乘除}//判斷是不是運算符public boolean isOperator(char value){return value == '+' || value == '-' || value == '*' || value == '/';}//兩數計算方法public int cal(int num1,int num2,char operator){int result = 0; //計算結果switch (operator){case '+':result = num2 + num1;break;case '-':result = num2 - num1;break;case '*':result = num2 * num1;break;case '/':result = num2 / num1;break;}return result;} }

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中綴表達式計算器類（測試類）

主要實現計算的邏輯。

public class Calculate {public static void main(String[] args) {String expression = "5+40*4-3"; //162AStack numStack = new AStack(10); //數棧AStack opeStack = new AStack(5); //運算符棧//定義需要的變量int index = 0; //用于掃描表達式int num1 = 0;int num2 = 0;int ope = 0;int res = 0; //用于臨時保存兩數運算結果char ch = ' '; //每次掃描得到的字符String keepNum = ""; //用于拼接多位數//掃描表達式while (true){//掃描一個表達式字符ch = expression.substring(index,index+1).charAt(0);//判斷ch是數還是運算符，并處理if (opeStack.isOperator(ch)) {//是運算符if (opeStack.isEmpty()){//運算符棧為空，直接入棧opeStack.push(ch);}else {//不為空if (opeStack.priority(ch) > opeStack.priority((char) opeStack.peek())){//新的運算符優先級大于棧頂運算符的優先級，直接入棧opeStack.push(ch);}else {//小于等于，則數棧pop兩個,運算符棧pop一個進行運算，將結果入數棧、新運算符入運算符棧num1 = numStack.pop();num2 = numStack.pop();ope = opeStack.pop();res = numStack.cal(num1,num2, (char) ope);numStack.push(res);opeStack.push(ch);}}}else {//是數keepNum += ch;if (index == expression.length() - 1){numStack.push(Integer.parseInt(keepNum));}else {if (numStack.isOperator(expression.substring(index+1,index+2).charAt(0))){//后一位是運算符，則當前的可以直接入數棧numStack.push(Integer.parseInt(keepNum));keepNum = ""; //清空}}}index++;if (index >= expression.length()){//掃描到最后break;}}//掃描結束，就順序pop運算符棧和數棧進行運算，如何每次將結果入數棧while (true){if (opeStack.isEmpty()){//運算符棧為空，則運算結束break;}num1 = numStack.pop();num2 = numStack.pop();ope = opeStack.pop();res = numStack.cal(num1,num2, (char) ope);numStack.push(res);}//數棧最后一個數即為表達式結果System.out.printf("表達式 %s = %d",expression,numStack.pop());} }

總結

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