java eval 字符串运算

最新推荐文章于 2022-03-04 15:25:09 发布

最新推荐文章于 2022-03-04 15:25:09 发布 · 817 阅读

文章标签：

#java #javascript #ViewUI

本文介绍了一个Java程序，用于解析和计算包含四则运算的数学表达式。该程序使用正则表达式来匹配和处理括号内的表达式，并通过递归方式解决复杂的数学问题。它还提供了两种不同的计算方法。

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http://www.ixueyun.com/community/home-space-uid-11902-do-blog-id-1923.html

http://www.4ucode.com/Study/Topic/450127

public class Eval {
    	
    	public Object eval2(String s) throws ScriptException, NoSuchMethodException{
    		if (s.replaceAll("[\\d+-\\\\*/()]","").equals("")) {    
                ScriptEngineManager manager = new ScriptEngineManager();
                ScriptEngine engine = manager.getEngineByName("JavaScript");
                engine.eval("function t() {return " + s + ";}");
                Invocable invocable = (Invocable) engine;
                Object o = invocable.invokeFunction("t");
                return o;
            }
    		return null;
    	}
    	
    	/**
    	 * 计算字符串四则运算表达式
    	 * @param string
    	 * @return
    	 * @author ZYWANG 2009-8-31
    	 */
    	public String eval(String string) {
    		String regexCheck = "[\\(\\)\\d\\+\\-\\*/\\.]*";// 是否是合法的表达式

    		if (!Pattern.matches(regexCheck, string))
    			return string;

    		Matcher matcher = null;
    		String temp = "";
    		int index = -1;
    		String regex = "\\([\\d\\.\\+\\-\\*/]+\\)";// 提取括号表达式
    		string = string.replaceAll("\\s", "");// 去除空格
    		try {
    			Pattern pattern = Pattern.compile(regex);
    			// 循环计算所有括号里的表达式
    			while (pattern.matcher(string).find()) {
    				matcher = pattern.matcher(string);
    				while (matcher.find()) {
    					temp = matcher.group();
    					index = string.indexOf(temp);
    					string = string.substring(0, index)
    							+ computeStirngNoBracket(temp)
    							+ string.substring(index + temp.length());
    				}
    			}
    			// 最后计算总的表达式结果
    			string = computeStirngNoBracket(string);
    		} catch (NumberFormatException e) {
    			return e.getMessage();
    		}
    		return string;
    	}

    	/**
    	 * 计算不包含括号的表达式
    	 * @param string
    	 * @return
    	 * @author ZYWANG 2009-8-31
    	 */
    	private  String computeStirngNoBracket(String string) {
    		string = string.replaceAll("(^\\()|(\\)$)", "");
    		String regexMultiAndDivision = "[\\d\\.]+(\\*|\\/)[\\d\\.]+";
    		String regexAdditionAndSubtraction = "(^\\-)?[\\d\\.]+(\\+|\\-)[\\d\\.]+";

    		String temp = "";
    		int index = -1;

    		// 解析乘除法
    		Pattern pattern = Pattern.compile(regexMultiAndDivision);
    		Matcher matcher = null;
    		while (pattern.matcher(string).find()) {
    			matcher = pattern.matcher(string);
    			if (matcher.find()) {
    				temp = matcher.group();
    				index = string.indexOf(temp);
    				string = string.substring(0, index) + doMultiAndDivision(temp)
    						+ string.substring(index + temp.length());
    			}
    		}

    		// 解析加减法
    		pattern = Pattern.compile(regexAdditionAndSubtraction);
    		while (pattern.matcher(string).find()) {
    			matcher = pattern.matcher(string);
    			if (matcher.find()) {
    				temp = matcher.group();
    				index = string.indexOf(temp);
    				if (temp.startsWith("-")) {
    					string = string.substring(0, index)
    							+ doNegativeOperation(temp)
    							+ string.substring(index + temp.length());
    				} else {
    					string = string.substring(0, index)
    							+ doAdditionAndSubtraction(temp)
    							+ string.substring(index + temp.length());
    				}
    			}
    		}

    		return string;
    	}

    	/**
    	 * 执行乘除法
    	 * @param string
    	 * @return
    	 * @author ZYWANG 2009-8-31
    	 */
    	private  String doMultiAndDivision(String string) {
    		String value = "";
    		double d1 = 0;
    		double d2 = 0;
    		String[] temp = null;
    		if (string.contains("*")) {
    			temp = string.split("\\*");
    		} else {
    			temp = string.split("/");
    		}

    		if (temp.length < 2)
    			return string;

    		d1 = Double.valueOf(temp[0]);
    		d2 = Double.valueOf(temp[1]);
    		if (string.contains("*")) {
    			value = String.valueOf(d1 * d2);
    		} else {
    			value = String.valueOf(d1 / d2);
    		}

    		return value;
    	}

    	/**
    	 * 执行加减法
    	 * @param string
    	 * @return
    	 * @author ZYWANG 2009-8-31
    	 */
    	private  String doAdditionAndSubtraction(String string) {
    		double d1 = 0;
    		double d2 = 0;
    		String[] temp = null;
    		String value = "";
    		if (string.contains("+")) {
    			temp = string.split("\\+");
    		} else {
    			temp = string.split("\\-");
    		}

    		if (temp.length < 2)
    			return string;

    		d1 = Double.valueOf(temp[0]);
    		d2 = Double.valueOf(temp[1]);
    		if (string.contains("+")) {
    			value = String.valueOf(d1 + d2);
    		} else {
    			value = String.valueOf(d1 - d2);
    		}

    		return value;
    	}

    	/**
    	 * 执行负数运算
    	 * @param string
    	 * @return
    	 * @author ZYWANG 2010-11-8
    	 */
    	private String doNegativeOperation(String string) {
    		String temp = string.substring(1);
    		if (temp.contains("+")) {
    			temp = temp.replace("+", "-");
    		} else {
    			temp = temp.replace("-", "+");
    		}
    		temp = doAdditionAndSubtraction(temp);
    		if (temp.startsWith("-")) {
    			temp = temp.substring(1);
    		} else {
    			temp = "-" + temp;
    		}
    		return temp;
    	}
    }
 
Eval eval = new Eval();
System.out.println(eval.eval("(1+(2+3)*2/5)*2/7+(3*7-3)*5")); 运行时间:0.007s
System.out.println(eval.eval2("(1+(2+3)*2/5)*2/7+(3*7-3)*5"));运行时间:0.118s  需要jdk6或者以上

java eval 字符串 运算

java eval 字符串运算