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数组模拟栈类

主要实现栈的一些基本功能，以及在该场景下的功能。

//先创建一个栈
class AStack {private int maxSize; //栈的大小private int[] stack; //数组模拟栈private int top = -1; //栈顶，初始化-1//构造器public AStack(int maxSize) {this.maxSize = maxSize;stack = new int[maxSize];}//栈满public boolean isFull(){return top == maxSize - 1;}//栈空public boolean isEmpty(){return top == -1;}//入栈public void push(int value){if (isFull()){System.out.println("栈满，入栈失败！");return;}top++;stack[top] = value;}//出栈public int pop(){if (isEmpty()){throw new RuntimeException("栈空，出栈失败！");}return stack[top--]; //先得到stack[top]，然后top--}//返回栈顶值public int peek(){return stack[top];}//遍历（从栈顶向下）public void show(){if (isEmpty()){System.out.println("栈空！");return;}for (int i = top; i >= 0; i--) {System.out.printf("stack[%d] = %d\n",i,stack[i]);}}//返回运算符优先级（约定数值越大，优先级越高）public int priority(char operator){if (operator == '*' || operator == '/'){return 1;}else if (operator == '+' || operator == '-'){return 0;}else return -1; //假设只有加减乘除}//判断是不是运算符public boolean isOperator(char value){return value == '+' || value == '-' || value == '*' || value == '/';}//两数计算方法public int cal(int num1,int num2,char operator){int result = 0; //计算结果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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中缀表达式计算器类（测试类）

主要实现计算的逻辑。

public class Calculate {public static void main(String[] args) {String expression = "5+40*4-3"; //162AStack numStack = new AStack(10); //数栈AStack opeStack = new AStack(5); //运算符栈//定义需要的变量int index = 0; //用于扫描表达式int num1 = 0;int num2 = 0;int ope = 0;int res = 0; //用于临时保存两数运算结果char ch = ' '; //每次扫描得到的字符String keepNum = ""; //用于拼接多位数//扫描表达式while (true){//扫描一个表达式字符ch = expression.substring(index,index+1).charAt(0);//判断ch是数还是运算符，并处理if (opeStack.isOperator(ch)) {//是运算符if (opeStack.isEmpty()){//运算符栈为空，直接入栈opeStack.push(ch);}else {//不为空if (opeStack.priority(ch) > opeStack.priority((char) opeStack.peek())){//新的运算符优先级大于栈顶运算符的优先级，直接入栈opeStack.push(ch);}else {//小于等于，则数栈pop两个,运算符栈pop一个进行运算，将结果入数栈、新运算符入运算符栈num1 = numStack.pop();num2 = numStack.pop();ope = opeStack.pop();res = numStack.cal(num1,num2, (char) ope);numStack.push(res);opeStack.push(ch);}}}else {//是数keepNum += ch;if (index == expression.length() - 1){numStack.push(Integer.parseInt(keepNum));}else {if (numStack.isOperator(expression.substring(index+1,index+2).charAt(0))){//后一位是运算符，则当前的可以直接入数栈numStack.push(Integer.parseInt(keepNum));keepNum = ""; //清空}}}index++;if (index >= expression.length()){//扫描到最后break;}}//扫描结束，就顺序pop运算符栈和数栈进行运算，如何每次将结果入数栈while (true){if (opeStack.isEmpty()){//运算符栈为空，则运算结束break;}num1 = numStack.pop();num2 = numStack.pop();ope = opeStack.pop();res = numStack.cal(num1,num2, (char) ope);numStack.push(res);}//数栈最后一个数即为表达式结果System.out.printf("表达式 %s = %d",expression,numStack.pop());}
}