JAVA中的eval , 能计算字符串的算数公式（源代码）

[a43350860]

public class Arithmetic {

public Arithmetic() {

}

/*操作区*/
private double operation(double n1,double n2,String expression){
if(expression.equals("+")){
return n1 + n2;
} else if(expression.equals("-")){
return n1 - n2;
} else if(expression.equals("*")){
return n1 * n2;
} else if(expression.equals("/")){
return n1 / n2;
}
return 0;
}

/*优先级*/
private int priority(String expression){
if(expression.equals("+") || expression.equals("-")){
return 0;
} else if(expression.equals("*") || expression.equals("/")){
return 1;
} else {
return -1;
}
}

/**
* 判断是否为一个算数运算符
* @param expression 算式运算符
* @return
*/
private boolean isExpression(String expression){
return expression.equals("+") || expression.equals("-") || expression.equals("*") || expression.equals("/") ;
}

/**
* 计算入口
* @param numModel 算式
* @return 结果
*/
public double doAccount(String numModel){
int endIndex = 0;
int startIndex = numModel.indexOf("(",endIndex);
while(startIndex != -1){
endIndex = numModel.indexOf(")", startIndex) + 1;
String segment = numModel.substring(startIndex,endIndex);

double tResult = account(segment.replace("(","").replace(")",""));
numModel = numModel.replace(segment,String.valueOf(tResult));

startIndex = numModel.indexOf("(",0);
}
DecimalFormat format = new DecimalFormat("0.##");
return Double.parseDouble(format.format(account(numModel)));
}

/**
* 核心算法逻辑
* @param numModel 算式
* @return
*/
@SuppressWarnings("unchecked")
private double account(String numModel){
String operators [] = {"\\+","\\-","\\*","\\/","\\(","\\)"};
for(String operator : operators){
numModel = numModel.replaceAll(operator," "+operator+" ");
}
Stack operStack = new Stack();
String numModels[] = numModel.split("\\s+");
String preEle = "";
for(int i = 0; i < numModels.length; i++){
if(isExpression(numModels[i])){
if(preEle == null || preEle.equals("")){
preEle = numModels[i];
} else {
if(priority(preEle) >= priority(numModels[i])){
double d1 = Double.parseDouble(String.valueOf(operStack.pop()));
double d2 = Double.parseDouble(String.valueOf(operStack.pop()));
operStack.push(operation(d2,d1,preEle));
preEle = numModels[i];
} else if(priority(preEle) < priority(numModels[i])){
double d1 = Double.parseDouble(String.valueOf(operStack.pop()));
double d2 = Double.parseDouble(numModels[i+1]);
operStack.push(operation(d1,d2,numModels[i]));
i++;
}
}
} else {
operStack.push(numModels[i]);
}
}

double d1 = Double.parseDouble(String.valueOf(operStack.pop()));
double d2 = Double.parseDouble(String.valueOf(operStack.pop()));
return operation(d2,d1,preEle);
}

/**
* @param args
*/
public static void main(String[] args) {
String numModel = "111.1 * (2 - 1) + (2 - 1) + 50 - 10 * (12 + 3)";
System.out.println(new Arithmetic().doAccount(numModel));
}
}

小弟也是一菜鸟，如果有什么不对的地方，还请大家多多指出来！

[yiliancangbai]

UP

[a43350860]

[Quote=引用 3 楼 bao110908 的回复:]
可以采用面向对象的方式来做，可以很方便地进行扩展，比如说再增加个 % 或 ^ 运算符。

你这个在计算 -5 + 9 时存在问题的。

参考这个帖子：http://topic.csdn.net/u/20081011/11/c69b34f6-7605-44a4-918b-a4bed78e8654.html
[/Quote]
谢谢！ 你的意思是说将运算符工厂化，这样再扩展运算符的时候，只需要修改实现类，而不用修改原程序！
我看看负数应该如何算！
原来JDK1.6有个脚本引擎！ 我改明也换个JDK玩玩！

[火龙果被占用了]

不一定要用 JDK 6 的 JavaScript Engine 哦，可以看看 BeanShell，BeanShell 是 JSR 274 规范的轻量级动态语言。

import bsh.EvalError;
import bsh.Interpreter;

public class Test {
    
    public static void main(String[] args) throws EvalError {
        double result = eval("111.1 * (2 - 1) + (2 - 1) + 50 - 10 * (12 + 3)");
        System.out.println(result);


        Interpreter bsh = new Interpreter();
        String expr = "int i = 5; j = 6";
        bsh.eval(expr);
        System.out.println("i = " + bsh.get("i"));
        System.out.println("j = " + bsh.get("j"));
    }
    
    private static double eval(String expression) throws EvalError {
        Interpreter bsh = new Interpreter();
        Number result = (Number)bsh.eval(expression);        
        return result.doubleValue();
    }
}

BeanShell: http://www.beanshell.org/

[nihuajie05]

这个代码真是让人...崩溃啊

[火龙果被占用了]

可以采用面向对象的方式来做，可以很方便地进行扩展，比如说再增加个 % 或 ^ 运算符。

你这个在计算 -5 + 9 时存在问题的。

参考这个帖子：http://topic.csdn.net/u/20081011/11/c69b34f6-7605-44a4-918b-a4bed78e8654.html

[a43350860]

[Quote=引用 5 楼 bao110908 的回复:]
不一定要用 JDK 6 的 JavaScript Engine 哦，可以看看 BeanShell，BeanShell 是 JSR 274 规范的轻量级动态语言。


Java codeimport bsh.EvalError;
import bsh.Interpreter;

public class Test {

public static void main(String[] args) throws EvalError {
double result = eval("111.1 * (2 - 1) + (2 - 1) + 50 - 10 * (12 + 3)");
System.out.println(result);


Interpr…
[/Quote]
哈哈，太好了，学习了！

[a43350860]

把代码重新改进了一下！ 不知道还有什么未知的bug ! 嘿嘿！

import java.text.DecimalFormat;
import java.util.HashMap;
import java.util.Map;
import java.util.Stack;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Arithmetic {

	public Arithmetic() {

	}

	/* 操作区 */
	private double operation(double n1, double n2, String expression) {
		if (expression.equals("+")) {
			return n1 + n2;
		} else if (expression.equals("-")) {
			return n1 - n2;
		} else if (expression.equals("*")) {
			return n1 * n2;
		} else if (expression.equals("/")) {
			return n1 / n2;
		}
		return 0;
	}

	/* 优先级 */
	private int priority(String expression) {
		if (expression != null && !expression.trim().equals("")) {
			if (expression.equals("+") || expression.equals("-")) {
				return 0;
			} else if (expression.equals("*") || expression.equals("/")) {
				return 1;
			}
		}
		return -1;
	}

	/**
	 * 判断是否为一个算数运算符
	 *
	 * @param expression
	 *            算式运算符
	 * @return
	 */
	private boolean isExpression(String expression) {
		return expression != null
				&& !expression.trim().equals("")
				&& (expression.equals("+") || expression.equals("-")
						|| expression.equals("*") || expression.equals("/"));
	}

	/**
	 * 计算入口
	 *
	 * @param numModel
	 *            算式
	 * @return 结果
	 */
	public double doAccount(String numModel) {
		try {
			int endIndex = 0;
			int startIndex = numModel.indexOf("(", endIndex);
			while (startIndex != -1) {
				endIndex = numModel.indexOf(")", startIndex) + 1;
				String segment = numModel.substring(startIndex, endIndex);

				double tResult = account(segment.replace("(", "").replace(")",
						""));
				numModel = numModel.replace(segment, String.valueOf(tResult));

				startIndex = numModel.indexOf("(", 0);
			}
			DecimalFormat format = new DecimalFormat("0.##");
			return Double.parseDouble(format.format(account(numModel)));
		} catch (Exception ex) {
			ex.printStackTrace();
		}
		return 0.0;
	}

	/**
	 * 核心算法逻辑
	 *
	 * @param numModel
	 *            算式
	 * @return
	 */
	@SuppressWarnings("unchecked")
	private double account(String numModel) throws Exception {

		try{
			return Double.parseDouble(numModel);
		} catch (NumberFormatException ex){}

		String operators[] = {"[.0-9]\\+","[.0-9]\\-", "\\*", "\\/", "\\(", "\\)" };
		for (int i = 0; i < operators.length; i++) {
			if(i == 0 || i == 1){
				Pattern pa = Pattern.compile(operators[i]);
				Matcher mt = pa.matcher(numModel);
				while(mt.find()){
					StringBuffer sb = new StringBuffer(mt.group());
					sb.insert(1," ");
					sb.append(" ");
					numModel = numModel.replaceAll(operators[i],sb.toString());
				}
			} else {
				numModel = numModel.replaceAll(operators[i]," "+operators[i]+" ");
			}
		}

		Stack operStack = new Stack();
		String numModels[] = numModel.split("\\s+");
		String preEle = "";
		for (int i = 0; i < numModels.length; i++) {
			if (isExpression(numModels[i])) {
				if (preEle == null || preEle.equals("")) {
					preEle = numModels[i];
				} else {
					if (priority(preEle) >= priority(numModels[i])) {
						double d1 = Double.parseDouble(String.valueOf(operStack
								.pop()));
						double d2 = Double.parseDouble(String.valueOf(operStack
								.pop()));
						operStack.push(operation(d2, d1, preEle));
						preEle = numModels[i];
					} else if (priority(preEle) < priority(numModels[i])) {
						double d1 = Double.parseDouble(String.valueOf(operStack
								.pop()));
						double d2 = Double.parseDouble(numModels[i + 1]);
						operStack.push(operation(d1, d2, numModels[i]));
						i++;
					}
				}
			} else {
				operStack.push(numModels[i]);
			}
		}

		double d1 = Double.parseDouble(String.valueOf(operStack.pop()));
		double d2 = Double.parseDouble(String.valueOf(operStack.pop()));
		return operation(d2, d1, preEle);
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		String numModel = "-1+(+1)-(+1*10)";
		System.out.println(new Arithmetic().doAccount(numModel));
	}

[gzfdxy]

import java.text.DecimalFormat;
import java.util.HashMap;
import java.util.Map;
import java.util.Stack;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Arithmetic {

public Arithmetic() {

}

/* 操作区 */
private double operation(double n1, double n2, String expression) {
if (expression.equals("+")) {
return n1 + n2;
} else if (expression.equals("-")) {
return n1 - n2;
} else if (expression.equals("*")) {
return n1 * n2;
} else if (expression.equals("/")) {
return n1 / n2;
}
return 0;
}

/* 优先级 */
private int priority(String expression) {
if (expression != null && !expression.trim().equals("")) {
if (expression.equals("+") || expression.equals("-")) {
return 0;
} else if (expression.equals("*") || expression.equals("/")) {
return 1;
}
}
return -1;
}

/**
* 判断是否为一个算数运算符
*
* @param expression
* 算式运算符
* @return
*/
private boolean isExpression(String expression) {
return expression != null
&& !expression.trim().equals("")
&& (expression.equals("+") || expression.equals("-")
|| expression.equals("*") || expression.equals("/"));
}

/**
* 计算入口
*
* @param numModel
* 算式
* @return 结果
*/
public double doAccount(String numModel) {
try {
int endIndex = 0;
int startIndex = numModel.indexOf("(", endIndex);
while (startIndex != -1) {
endIndex = numModel.indexOf(")", startIndex) + 1;
String segment = numModel.substring(startIndex, endIndex);

double tResult = account(segment.replace("(", "").replace(")",
""));
numModel = numModel.replace(segment, String.valueOf(tResult));

startIndex = numModel.indexOf("(", 0);
}
DecimalFormat format = new DecimalFormat("0.##");
return Double.parseDouble(format.format(account(numModel)));
} catch (Exception ex) {
ex.printStackTrace();
}
return 0.0;
}

/**
* 核心算法逻辑
*
* @param numModel
* 算式
* @return
*/
@SuppressWarnings("unchecked")
private double account(String numModel) throws Exception {

try{
return Double.parseDouble(numModel);
} catch (NumberFormatException ex){}

String operators[] = {"[.0-9]\\+","[.0-9]\\-", "\\*", "\\/", "\\(", "\\)" };
for (int i = 0; i < operators.length; i++) {
if(i == 0 || i == 1){
Pattern pa = Pattern.compile(operators[i]);
Matcher mt = pa.matcher(numModel);
while(mt.find()){
StringBuffer sb = new StringBuffer(mt.group());
sb.insert(1," ");
sb.append(" ");
numModel = numModel.replaceAll(operators[i],sb.toString());
}
} else {
numModel = numModel.replaceAll(operators[i]," "+operators[i]+" ");
}
}

Stack operStack = new Stack();
String numModels[] = numModel.split("\\s+");
String preEle = "";
for (int i = 0; i < numModels.length; i++) {
if (isExpression(numModels[i])) {
if (preEle == null || preEle.equals("")) {
preEle = numModels[i];
} else {
if (priority(preEle) >= priority(numModels[i])) {
double d1 = Double.parseDouble(String.valueOf(operStack
.pop()));
double d2 = Double.parseDouble(String.valueOf(operStack
.pop()));
operStack.push(operation(d2, d1, preEle));
preEle = numModels[i];
} else if (priority(preEle) < priority(numModels[i])) {
double d1 = Double.parseDouble(String.valueOf(operStack
.pop()));
double d2 = Double.parseDouble(numModels[i + 1]);
operStack.push(operation(d1, d2, numModels[i]));
i++;
}
}
} else {
operStack.push(numModels[i]);
}
}

double d1 = Double.parseDouble(String.valueOf(operStack.pop()));
double d2 = Double.parseDouble(String.valueOf(operStack.pop()));
return operation(d2, d1, preEle);
}

/**
* @param args
*/
public static void main(String[] args) {
String numModel = "-1+(+1)-(+1*10)";
System.out.println(new Arithmetic().doAccount(numModel));
}

[火龙果被占用了]

带有嵌套括号的有问题：

String numModel = "1 + (2 * (3 + 4) * 5)";

[a43350860]

[Quote=引用 9 楼 bao110908 的回复:]
带有嵌套括号的有问题：
Java codeString numModel = "1 + (2 * (3 + 4) * 5)";
[/Quote]
我把doAccount方法改了一下，解决了括号问题！
代码如下:

/**
	 * 计算入口
	 *
	 * @param numModel
	 *            算式
	 * @return 结果
	 */
	public double doAccount(String numModel) {
		try {
			int eIndex = numModel.indexOf(")");
			int bIndex = numModel.lastIndexOf("(",eIndex);

			if(eIndex != -1 && bIndex == -1){
				throw new Exception("算式格式不正确!!");
			} else if(eIndex == -1 && bIndex != -1) {
				throw new Exception("算式格式不正确!!");
			}

			String segment = numModel.substring(bIndex, eIndex+1);
			String tempSegment = segment.replace("(", "").replace(")","");
			double tResult = account(tempSegment);
			numModel = numModel.replace(segment,String.valueOf(tResult));

			if(numModel.indexOf(")") != -1){
				return doAccount(numModel);
			}

			DecimalFormat format = new DecimalFormat("0.##");
			return Double.parseDouble(format.format(account(numModel)));
		} catch (Exception ex) {
			ex.printStackTrace();
		}
		return 0.0;
	}

谢谢bao110908，
你是一个很有经验的人，想得很周到，看得很仔细. 有时间，多多交流！

[SheLiZi]

5楼的方法挺好，学习了！