数学表达式计算程序(java)


现在仅支持正负号、加减乘除、次方和模运算
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public class Test { public static void main(String[] args) { String str = " 40944.0501-3.2*100 " ; Calculator cal = new Calculator(); double d = cal.eval(str); System.out.println(d); } } public interface MathSymbol { /** * 左括号 */ public final static char LEFT_BRACKET = ' ( ' ; /** * 右括号 */ public final static char RIGHT_BRACKET = ' ) ' ; /** * 中缀表达式中的空格,需要要忽略 */ public final static char BLANK = ' ' ; /** * 小数点符号 */ public final static char DECIMAL_POINT = ' . ' ; /** * 负号 */ public final static char NEGATIVE_SIGN = ' - ' ; /** * 正号 */ public final static char POSITIVE_SIGN = ' + ' ; /** * 后缀表达式的各段的分隔符 */ public final static char SEPARATOR = ' ' ; } import java.util.Stack; public class Calculator implements MathSymbol { /** * 计算中缀表达式 * @param expression * @return */ public double eval(String expression) { String str = infix2Suffix(expression); // System.out.println(" Infix Expression: " + expression); // System.out.println("Suffix Expression: " + str); if (str == null ) { throw new IllegalArgumentException( " Expression is null! " ); } String[] strs = str.split( " //s+ " ); Stack < String > stack = new Stack < String > (); for ( int i = 0 ; i < strs.length; i ++ ) { if ( ! Operator.isOperator(strs[i])) { stack.push(strs[i]); } else { Operator op = Operator.getInstance(strs[i]); double right = Double.parseDouble(stack.pop()); double left = Double.parseDouble(stack.pop()); double result = op.eval(left, right); stack.push(String.valueOf(result)); } } return Double.parseDouble(stack.pop()); } /** * 将中缀表达式转换为后缀表达式 * @param expression * @return */ public String infix2Suffix(String expression) { if (expression == null ) { return null ; } char [] chs = expression.toCharArray(); Stack < Character > stack = new Stack < Character > (); StringBuilder sb = new StringBuilder(chs.length); boolean appendSeparator = false ; boolean sign = true ; for ( int i = 0 ; i < chs.length; i ++ ) { char c = chs[i]; if (c == BLANK) { continue ; } // Next line is used output stack information. // System.out.printf("%-20s %s%n", stack, sb.toString()); if (appendSeparator) { sb.append(SEPARATOR); appendSeparator = false ; } if (isSign(c) && sign) { sb.append(c); continue ; } if (isNumber(c)) { sign = false ; sb.append(c); continue ; } if (isLeftBracket(c)) { stack.push(c); continue ; } if (isRightBracket(c)) { sign = false ; while (stack.peek() != LEFT_BRACKET) { sb.append(SEPARATOR); sb.append(stack.pop()); } stack.pop(); continue ; } appendSeparator = true ; if (Operator.isOperator(c)) { sign = true ; if (stack.isEmpty() || stack.peek() == LEFT_BRACKET) { stack.push(c); continue ; } int precedence = Operator.getPrority(c); while ( ! stack.isEmpty() && Operator.getPrority(stack.peek()) >= precedence) { sb.append(SEPARATOR); sb.append(stack.pop()); } stack.push(c); } } while ( ! stack.isEmpty()) { sb.append(SEPARATOR); sb.append(stack.pop()); } return sb.toString(); } /** * 判断某个字符是否是正号或者负号 * @param c * @return */ private boolean isSign( char c) { if (c == NEGATIVE_SIGN || c == POSITIVE_SIGN) { return true ; } return false ; } /** * 判断某个字符是否为数字或者小数点 * @param c * @return */ private boolean isNumber( char c) { if ((c >= ' 0 ' && c <= ' 9 ' ) || c == DECIMAL_POINT) { return true ; } return false ; } /** * 判断某个字符是否为左括号 * @param c * @return */ private boolean isLeftBracket( char c) { return c == LEFT_BRACKET; } /** * 判断某个字符是否为右括号 * @param c * @return */ private boolean isRightBracket( char c) { return c == RIGHT_BRACKET; } }
    
    
    
    
Java code
      
      
      
      
import java.util.HashMap; import java.util.Map; public abstract class Operator { /** * 运算符 */ private char operator; /** * 运算符的优先级别,数字越大,优先级别越高 */ private int priority; private static Map < Character, Operator > operators = new HashMap < Character, Operator > (); private Operator( char operator, int priority) { setOperator(operator); setPriority(priority); register( this ); } private void register(Operator operator) { operators.put(operator.getOperator(), operator); } /** * 加法运算 */ public final static Operator ADITION = new Operator( ' + ' , 100 ) { public double eval( double left, double right) { return left + right; } }; /** * 减法运算 */ public final static Operator SUBTRATION = new Operator( ' - ' , 100 ) { public double eval( double left, double right) { return left - right; } }; /** * 乘法运算 */ public final static Operator MULTIPLICATION = new Operator( ' * ' , 200 ) { public double eval( double left, double right) { return left * right; } }; /** * 除法运算 */ public final static Operator DIVITION = new Operator( ' / ' , 200 ) { public double eval( double left, double right) { return left / right; } }; /** * 冪运算 */ public final static Operator EXPONENT = new Operator( ' ^ ' , 300 ) { public double eval( double left, double right) { return Math.pow(left, right); } }; /** * 取模运算 */ public final static Operator MOD = new Operator( ' % ' , 200 ) { public double eval( double left, double right) { return left % right; } }; public char getOperator() { return operator; } private void setOperator( char operator) { this .operator = operator; } public int getPriority() { return priority; } private void setPriority( int priority) { this .priority = priority; } /** * 根据某个运算符获得该运算符的优先级别 * @param c * @return 运算符的优先级别 */ public static int getPrority( char c) { Operator op = operators.get(c); if (op != null ) { return op.getPriority(); } return 0 ; } /** * 工具方法,判断某个字符是否是运算符 * @param c * @return 是运算符返回 true,否则返回 false */ public static boolean isOperator( char c) { return getInstance(c) != null ; } public static boolean isOperator(String str) { if (str.length() > 1 ) { return false ; } return isOperator(str.charAt( 0 )); } /** * 根据运算符获得 Operator 实例 * @param c * @return 从注册中的 Operator 返回实例,尚未注册返回 null */ public static Operator getInstance( char c) { return operators.get(c); } public static Operator getInstance(String str) { if (str.length() > 1 ) { return null ; } return getInstance(str.charAt( 0 )); } /** * 根据操作数进行计算 * @param left 左操作数 * @param right 右操作数 * @return 计算结果 */ public abstract double eval( double left, double right); }

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