通過棧的數據結構實現一個計算器
詳解見註釋
package stack;
public class Calculator
{
public static void main(String[] args)
{
//表達式
String expression = "3+20*6-20";
//創建兩個棧,一個符號棧,一個數棧
ArrayStack2 numStack = new ArrayStack2(10);
ArrayStack2 operStack = new ArrayStack2(10);
//定義需要的相關變量
int index = 0;//用於掃描
int num1 = 0;
int num2 = 0;
int oper = 0;
int res = 0;
char ch = ' '; //每次掃描到的char保存到ch
String keepNum = ""; //多位數
//開始while循環的
while(true)
{
//依次得到expression的每一個字符
ch = expression.substring(index, index+1).charAt(0);
//判斷ch是什麼,然後再做處理
if(operStack.isOper(ch)) //如果是運算符
{
if(!operStack.isEmpty())//判斷當前棧是否爲空
{
if(operStack.priority(ch) <= operStack.priority(operStack.peek()))
{
num1 = numStack.pop();
num2 = numStack.pop();
oper= operStack.pop();
res = numStack.cal(num1, num2, oper);
//運算結果入棧
numStack.push(res);
operStack.push(ch);
}
else
{
//如果當前的操作符的優先級大於棧中的操作符,就直接入符號棧
operStack.push(ch);
}
}
else
{
//如果爲空,直接入符號棧
operStack.push(ch);
}
}
else
{
// //如果是數,直接入數棧
// numStack.push(ch - 48); //'1' + '3' = >1 (阿斯克碼)
//處理多位數
keepNum = keepNum + ch;
//如果ch已經是expression的最後一位,就直接入棧
if(index == expression.length() - 1)
{
numStack.push(Integer.parseInt(keepNum));
}
else
{
//判斷下一個是不是數字,如果是數字,就繼續掃描,運算符啊,則入棧
if(operStack.isOper(expression.substring(index+1, index+2).charAt(0)))
{
numStack.push(Integer.parseInt(keepNum));
keepNum = ""; //置空
}
}
}
//讓index+1,並判斷是否掃描到expression最後
index++;
if(index >= expression.length())
{
break;
}
}
//當表達式掃描完畢,就順序的從數棧 + 符號棧中pop相應的數和符號,並運行
while(true)
{
if(operStack.isEmpty())
{
break;
}
//如果符號棧爲空,則計算到最後結果
num1 = numStack.pop();
num2 = numStack.pop();
oper = operStack.pop();
res = numStack.cal(num1, num2, oper);
numStack.push(res); //入棧
}
//將數棧的最後數,pop;
System.out.printf("表達式%s = %d", expression, numStack.pop());
}
}
//定義一個ArrayStack表示棧
class ArrayStack2
{
private int maxSize; //最大容量
private int[] stack; //數組模擬棧,數據就放在該數組中
private int top = -1; //top表示棧頂,初始化爲-1
//構造器
public ArrayStack2(int maxSize)
{
this.maxSize = maxSize;
stack = new int[this.maxSize];
}
//增加一個方法,可以返回當前棧頂的值,但不是真正的pop
public int peek()
{
return stack[top];
}
//判斷是否棧滿
public boolean isFull()
{
return top == maxSize-1;
}
//判斷是否棧空
public boolean isEmpty()
{
return top == -1;
}
//入棧
public void push(int value)
{
if(isFull())
{
System.out.println("棧已滿~");
return;
}
top++;
stack[top] = value;
}
//出棧
public int pop()
{
if(isEmpty())
throw new RuntimeException("棧已空,無數據~");
int value = stack[top];
top--;
return value;
}
//顯示棧的情況,遍歷棧
public void list()
{
if(isEmpty())
{
System.out.println("棧空,沒有數據~");
return;
}
for(int i=top;i>=0;i--)
{
System.out.printf("stack[%d]=%d\n",i,stack[i]);
}
}
//返回運算器的優先級,數字越大,優先級越高
public int priority(int oper)
{
if(oper == '*' || oper == '/')
{
return 1;
}
else if(oper == '+' || oper == '-')
{
return 0;
}
else
return -1; //假定目前表達式只有
}
//判斷是不是運算符
public boolean isOper(char val)
{
return val == '+' || val == '-' || val == '*' || val == '/';
}
//計算方法
public int cal(int num1, int num2, int oper)
{
int res = 0; //用於存放結果
switch(oper)
{
case '+':
res = num2 + num1;
break;
case '-':
res = num2 - num1;
break;
case '*':
res = num2 * num1;
break;
case '/':
res = num2 / num1;
break;
default:
break;
}
return res;
}
}