用Java代码写出输入表达式就可以求出具体值的代码，用栈或者队列的形式
用Java代码写出输入表达式就可以求出具体值的代码，用栈或者队列的形式
public class Stack<T> {
//节点类
public class Node{
public T data;
public Node next;
public Node(){}
public Node(T data,Node next){
this.data = data;
this.next = next;
}
}//Node
public Node top = new Node();
public int size;
public Node oldNode;
//入栈
public void push(T element){
top = new Node(element,top);
size++;
}
//出栈
public T pop(){
oldNode = top;
top = top.next;
//oldNode = null;
size--;
return oldNode.data;
}
//返回栈顶对象的数据域，但不出栈
public T peek(){
return top.data;
}
//栈长
public int length(){
return size;
}
//判断栈是否为空
public boolean isEmpty(){
return size == 0;
}
}
import java.util.Scanner;
public class Test {
public static final char[][] relation = {{'>','>','<','<','<','>','>'},
{'>','>','<','<','<','>','>'},{'>','>','>','>','<','>','>'},
{'>','>','>','>','<','>','>'},{'<','<','<','<','<','=','!'},
{'>','>','>','>','!','>','>'},{'<','<','<','<','<','!','='}};
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
while(true){
try{
System.out.println("请输入要计算的表达式：");
String exp = input.next();
System.out.println(calc(exp + "#"));
}catch(ArithmeticException e1){
System.out.println("表达式中的分母不能为0");
e1.printStackTrace();
}
}
}
/**
*
* @param exp 要计算的表达式
* @return 计算的结果
*/
private static int calc(String exp) {
//操作数栈
Stack<Integer> num = new Stack<Integer>();
//操作符栈
Stack<Character> op = new Stack<Character>();
op.push('#');
int i = 0;
char ch = exp.charAt(i);
boolean flag = false;//判断连续的几个字符是否是数字，若是，就处理成一个数字。这样就能处理多位数的运算了。
while(ch != '#' || op.peek() != '#') {//peek()查看栈顶对象但不移除。
if(ch >= '0' && ch <= '9') {
if(flag) {
int tmp = num.pop();
num.push(tmp * 10 + Integer.parseInt(ch + ""));
} else {
num.push(Integer.parseInt(ch + ""));
}
flag = true;
i++;
} else {
flag = false;
switch(precede(op.peek(), ch)) {
case '<':
op.push(ch);
i++;
break;
case '=':
op.pop();
i++;
break;
case '>':
int num2 = num.pop();
int num1 = num.pop();
int result = operate(num1, op.pop(), num2);
num.push(result);
break;
case '!':
System.out.println("输入的表达式错误！");
return -1;
}
}
ch = exp.charAt(i);
}
return num.peek();
}
private static char precede(char peek, char ch) {
return relation[getIndex(peek)][getIndex(ch)];
}
/**
*
* @param ch 操作符
* @return 操作符的索引，按照+、-、*、/、（、）的顺序
*/
private static int getIndex(char ch) {
int index = -1;
switch(ch) {
case '+':
index = 0;
break;
case '-':
index = 1;
break;
case '*':
index = 2;
break;
case '/':
index = 3;
break;
case '(':
index = 4;
break;
case ')':
index = 5;
break;
case '#':
index = 6;
break;
}
return index;
}
/**
*
* @param num1 第一个运算数
* @param ch 运算符
* @param num2 第二个运算数
* @return 运算结果
*/
private static int operate(int num1, char ch, int num2) {
int result = 0;
switch(ch) {
case '+':
result = num1 + num2;
break;
case '-':
result = num1 - num2;
break;
case '*':
result = num1 * num2;
break;
case '/':
result = num1 / num2;
break;
}
return result;
}
}