Java 实现计算表达式（接受小数点）

小咪咪 2024-04-08 09:29 76阅读 0赞

**Java 实现计算表达式**

列入计算：2\*(120/20+(40+20)\*10-80+20-6)

思路：把数字和操作字符装入2个栈中，根据操作字符的优先级计算，最后数中留下计算结果。

public class CalculationUtils {
        
    
        private Stack<Character> chars;
        private Stack<Double> result;
    
        public Double calculation(String expression) {
        
            expression = expression == null ? "" : expression + "=";
            //校验 （）匹配
            Stack<Character> brackets = new Stack<>();
            for (int i = 0; i < expression.length(); i++) {
        
                char c = expression.charAt(i);
                if (!(isNumber(c)
                        || "+".equals(c + "")
                        || "-".equals(c + "")
                        || "*".equals(c + "")
                        || "/".equals(c + "")
                        || "=".equals(c + "")
                        || "(".equals(c + "")
                        || ")".equals(c + "")
                        || ".".equals(c + "")
                )) {
        
                    //结束程序
                    return (double) -1;
                }
                if ("(".equals(c + "")) {
        
                    brackets.push(c);
                }
                if (")".equals(c + "")) {
        
                    if (brackets.empty() || !"(".equals(brackets.pop() + "")) {
        
                        //结束程序
                        return (double) -1;
                    }
                }
            }
            if (!brackets.isEmpty()) {
        
                //结束程序
                return (double) -1;
            }
            chars = new Stack<>();
            result = new Stack<>();
            //缓存多位操作数
            StringBuilder stringBuffer = new StringBuilder();
            // 计算
            for (int i = 0; i < expression.length(); i++) {
        
                char c = expression.charAt(i);
                if (isNumber(c)) {
        
                    stringBuffer.append(c);
                } else {
        
                    //加入数字
                    if (!"".equals(stringBuffer.toString())) {
        
                        result.push(Double.parseDouble(stringBuffer.toString()));
                        stringBuffer = new StringBuilder();
                    }
                    // 栈顶有符号 且c的优先级小于等于栈顶的优先级 一直计算
                    while (!chars.isEmpty() && priority(c)) {
        
                        Double after = result.pop();
                        Double before = result.pop();
                        char operation = chars.pop();
                        switch (operation) {
        
                            case '+':
                                result.push(before + after);
                                break;
                            case '-':
                                result.push(before - after);
                                break;
                            case '*':
                                result.push(before * after);
                                break;
                            case '/':
                                result.push(before / after);
                                break;
                            default:
                        }
                    }
                    if (!"=".equals(c + "")) {
        
                        chars.push(c);
                        if (")".equals(c + "")) {
        
                            chars.pop();
                            chars.pop();
                        }
                    }
                }
            }
            //返回计算结果
            return result.pop();
        }
    
        private boolean priority(char c) {
        
            if ("(".equals(chars.peek() + "")) {
        
                return false;
            }
            //c 需要入符号栈
            char peek = chars.peek();
            switch (c) {
        
                case '.':
                case '+':
                case '=':
                case '-':
                case ')':
                    //不入栈 去计算
                    return true;
                case '*':
                case '/': {
        
                    if (peek == '+' || peek == '-') {
        
                        return false;
                    }
                    return true;
                }
                case '(':
                    return false;
                default:
            }
    
            return false;
        }
    
        public boolean isNumber(Character number) {
        
            return (number <= 57 && number >= 48) || number == '.';
        }
    }

![在这里插入图片描述][ca4ca7a25ca9478e9a6ae41ca5a99aa1.png]

[ca4ca7a25ca9478e9a6ae41ca5a99aa1.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/08/4432a342b53744a9ac832668869598cf.png