Java命令行计算器（中缀表达式求值）

秒速五厘米 2023-06-12 11:08 12阅读 0赞

/**
     * 加减乘除计算器
     * 支持带括号的整数优先级运算
     * 输入一个中缀表达式，符号与数字用空格隔开，例如 ( 1 + 2 ) * 3 - 4
     * 输出运算结果
     * */
    import java.util.Scanner;
    import java.util.Stack;
    
    public class Calculator{
        
    	public static int getPriority(String op){
          //获取操作符优先级
    		if(op.equals("+") || op.equals("-")){
        
    			return 1;
    		}else if(op.equals("*") || op.equals("/")){
        
    			return 2;
    		}else if(op.equals("(")){
           //栈外括号优先级最大，栈内最小
    			return 0;
    		}else if(op.equals("=")){
        
    			return -1;
    		}else
    			return -1;
    	}
    	
    	public static boolean isNum(String str){
          //判断字符串是否为数字
    		if(str.charAt(0) == '-'){
          //处理负数
    			if(str.length() == 1) {
        
    				return false;
    			}else {
        
    				for(int i = 1; i < str.length(); i++){
        
    					if(!Character.isDigit(str.charAt(i))){
        
    						return false;
    					}
    				}
    			}
    		}else {
        
    			for(int i = 0; i < str.length(); i++){
        
    				if(!Character.isDigit(str.charAt(i))){
        
    					return false;
    				}
    			}
    		}		
    		return true;
    	}
    	
    	public static int operation(int a,int b,String op){
          //根据运算符进行运算
    		int result = 0;
    		if(op.equals("+"))
    			result = a + b;
    		else if(op.equals("-"))
    			result = a - b;
    		else if(op.equals("*"))
    			result = a * b;
    		else if(op.equals("/"))
    			result = a / b;
    		return result;
    	}
    	
    	public static void main(String[] args){
        
    		Scanner sc = new Scanner(System.in);
    		String str = sc.nextLine();
    		String[] expr = str.split("\\s+");  //根据空格分割字符串
    		
    		Stack<Integer> opNum = new Stack<Integer>();  //数字栈
    		Stack<String> opSign = new Stack<String>();  //操作符栈
    		opSign.push("=");
    		
    		for(String s : expr){
        
    			if(isNum(s)){
          //遇到数字，直接压栈
    				int num = Integer.parseInt(s);
    				opNum.push(num);
    			}else if(s.equals("(")){
          //遇到左括号，直接压栈
    				opSign.push(s);
    			}
    			else if(s.equals(")")){
        
    				while(true) {
        
    					String op = opSign.pop();
    					if(op.equals("("))  //弹出左括号，结束
    						break;
    					else {
          //不是左括号，则为操作符，进行运算
    						int right = opNum.pop();
    						int left = opNum.pop();
    						int re = operation(left,right,op);
    						opNum.push(re);
    					}
    				}
    			}else{
          //遇到的是+ - * /
    				while(true){
        
    					if(getPriority(s) > getPriority(opSign.peek())){
        
    						opSign.push(s);  //当前符号优先级比栈顶符号优先级高，直接入栈
    						break;
    					}else{
          
    						int right = opNum.pop();
    						int left = opNum.pop();
    						String op = opSign.pop();
    						int re = operation(left,right,op);
    						opNum.push(re);
    					}
    				}				
    			}
    		}
    		while(!opSign.peek().equals("=")){
          //对栈中剩余数进行运算
    			int right = opNum.pop();
    			int left = opNum.pop();
    			String op = opSign.pop();
    			int re = operation(left,right,op);
    			opNum.push(re);
    		}
    		System.out.println(opNum.pop());
    	}
    }