java中有没有像js中eval函数的方法？

Question

有一个字符串“4+3”我在java中怎么能执行4+3得到7呢

Answer 1

在JAVA中用反射可以实现类似的功能

Answer 2

在JAVA中我还没有见过类似Javascript中eval的这种功能除非自己写一个组件来实现,我说的用反射进行就是下面的代码.
import java.lang.reflect.*;public class ReflactTest{

public static void main(String[] args){
try{
Class addClass=Class.forName("AddTest");
Method[] method=addClass.getMethods();

System.out.println(method[0].invoke(new AddTest(),new Object[]{3,4}));
} catch (Exception e){
e.getMessage();
}
}
}class AddTest{
private int add1;
private int add2;

public AddTest(){}

public int add(int add1,int add2){
return add1+add2;
}
}

Answer 3

因为JAVA是一个面向对象的语言,我想象JS中的那种功能放到JAVA中不太适合.在JAVA中,语句都是在某一个类之中的,没有独立的语句存在.因此我想这种功能不会在JAVA API中出现,当然,这只是我的想法,未来的事情谁都说不清楚...

Answer 4

早已有高人写过这个了，google一下就有了

Answer 5

代码太长，分两部分贴上package mathTools;
/**
 * Eval.java
 *
 * Created on 2006年4月10日, 下午3:46
 *
 * To change this template, choose Tools | Template Manager
 * and open the template in the editor.
 *
 * 支持运算符：+ - * / % > < ] [ ! | & =
 *      其中：
 *           ]  表示大于等于
 *           [  表示小于等于
 *           ！ 表示不等于
 *           ｜ 表示或
 *           ＆ 表示与
 *           ＝ 表示是否等于
 *
 * 支持函数：sqrt,square,ceil,sin,cos,asin,acon.tan.atan,log,exp 具体含义见 calFunction 代码
 *
 *//**
 *
 * @author Trumplet
 *
 */import java.util.Stack;
import java.util.regex.Matcher;
import java.util.regex.Pattern;public class Eval{
    public static String OPTS="+-*/%><][!|&=#";
    public Object calculate(String expression) throws ExpressionException{
        try {
            Stack Opts=new Stack();
            Stack Values=new Stack();
            String exp=expression+"#";
            int nCount=exp.length(),nIn,nOut,nTemp;
            Opts.push("#");
            String temp="",optOut="",optIn="",value1="",value2="",optTemp="",opt="",temp1="";
            int nFun=0;
            boolean isFun=false;
            for(int i=0;i<nCount;){
                nTemp=0;
                opt=exp.substring(i,i+1);
                isFun=false;
                temp1="";
                while(i<nCount){
                    if(!temp1.equals("")){
                        if(opt.equals("(")){
                            nFun++;
                            isFun=true;
                        } else if(opt.equals(")")){
                            nFun--;
                        }
                    }
                    if((nFun>0)||((!isFun)&&this.isValue(opt))){
                        temp1+=opt;
                        nTemp++;
                        opt=exp.substring(i+nTemp,i+nTemp+1);
                    } else{
                        if(isFun){
                            temp1+=opt;
                            nTemp++;
                        }
                        break;
                    }
                }
                if(temp1.equals("")){
                    temp=opt;
                } else{
                    temp=temp1;
                }
                if(nTemp>0){
                    i=i+nTemp-1;
                }
                temp=temp.trim();
                
                if(this.isValue(temp)){
                    temp=this.getValue(temp);
                    Values.push(temp);
                    i++;
                } else{
                    optIn=Opts.pop().toString();
                    nIn=this.getOptPriorityIn(optIn);
                    nOut=this.getOptPriorityOut(temp);
                    if(nIn==nOut){
                        i++;
                    } else if(nIn>nOut){
                        String ret="";
                        value1=Values.pop().toString();
                        value2=Values.pop().toString();
                        ret=String.valueOf(this.calValue(value2,optIn,value1));
                        Values.push(ret);
                    } else if(nIn<nOut){
                        Opts.push(optIn);
                        Opts.push(temp);
                        i++;
                    }
                }
            }
            return Values.pop();
        } catch(ExpressionException eE) {
            throw eE;
        } catch(Exception e) {
            throw new ExpressionException("表达式"+expression+"格式非法!");
        }
    }
    
    protected int getOptPriorityOut(String opt)throws ExpressionException{
        if(opt.equals("+")){
            return 1;
        } else if(opt.equals("-")){
            return 2;
        } else if(opt.equals("*")){
            return 5;
        } else if(opt.equals("/")){
            return 6;
        } else if(opt.equals("%")){
            return 7;
        } else if(opt.equals(">")){
            return 11;
        } else if(opt.equals("<")){
            return 12;
        } else if(opt.equals("]")){
            return 13;
        } else if(opt.equals("[")){
            return 14;
        } else if(opt.equals("!")){
            return 15;
        } else if(opt.equals("|")){
            return 16;
        } else if(opt.equals("&")) {
            return 23;
        } else if(opt.equals("=")) {
            return 25;
        } else if(opt.equals("#")) {
            return 0;
        } else if(opt.equals("(")){
            return 1000;
        } else if(opt.equals(")")){
            return -1000;
        }
        throw new ExpressionException("运算符"+opt+"非法!");
    }
    
    protected int getOptPriorityIn(String opt) throws ExpressionException{
        if(opt.equals("+")){
            return 3;
        } else if(opt.equals("-")){
            return 4;
        } else if(opt.equals("*")){
            return 8;
        } else if(opt.equals("/")){
            return 9;
        } else if(opt.equals("%")){
            return 10;
        } else if(opt.equals(">")){
            return 17;
        } else if(opt.equals("<")){
            return 18;
        } else if(opt.equals("]")){
            return 19;
        } else if(opt.equals("[")){
            return 20;
        } else if(opt.equals("!")){
            return 21;
        } else if(opt.equals("|")){
            return 22;
        } else if(opt.equals("&")) {
            return 24;
        } else if(opt.equals("=")) {
            return 26;
        } else if(opt.equals("(")){
            return -1000;
        } else if(opt.equals(")")){
            return 1000;
        } else if(opt.equals("#")){
            return 0;
        }
        throw new ExpressionException("运算符"+opt+"非法！");
    }

Answer 6

    protected String getOPTS() {
        return OPTS;
    }
    protected boolean isValue(String cValue){
        String notValue=this.getOPTS()+"()";
        return notValue.indexOf(cValue)==-1;
    }
    
    protected boolean isOpt(String value){
        return this.getOPTS().indexOf(value)>=0;
    }
    
    protected double calValue(String value1,String opt,String value2) throws ExpressionException{
        try {
            double dbValue1=Double.valueOf(value1).doubleValue();
            double dbValue2=Double.valueOf(value2).doubleValue();
            long lg=0;
            if(opt.equals("+")){
                return dbValue1+dbValue2;
            } else if(opt.equals("-")){
                return dbValue1-dbValue2;
            } else if(opt.equals("*")){
                return dbValue1*dbValue2;
            } else if(opt.equals("/")){
                return dbValue1/dbValue2;
            } else if(opt.equals("%")){
                lg=(long)(dbValue1/dbValue2);
                return dbValue1-lg*dbValue2;
            } else if(opt.equals(">")){
                if(dbValue1>dbValue2)
                    return 1;
                else
                    return 0;
            } else if(opt.equals("<")){
                if(dbValue1<dbValue2)
                    return 1;
                else
                    return 0;
            } else if(opt.equals("]")){
                if(dbValue1>=dbValue2)
                    return 1;
                else
                    return 0;
            } else if(opt.equals("[")){
                if(dbValue1<=dbValue2)
                    return 1;
                else
                    return 0;
            } else if(opt.equals("!")){
                if(dbValue1!=dbValue2)
                    return 1;
                else
                    return 0;
            } else if(opt.equals("|")){
                if(dbValue1>0||dbValue2>0)
                    return 1;
                else
                    return 0;
            } else if(opt.equals("&")){
                if(dbValue1>0&&dbValue2>0)
                    return 1;
                else
                    return 0;
            } else if(opt.equals("=")){
                if(dbValue1==dbValue2)
                    return 1;
                else
                    return 0;
            }
        }catch(Exception e) {
            throw new ExpressionException("值"+value1+"或"+value2+"在进行"+ opt+"运算时非法！");
        }
        throw new ExpressionException("运算符"+opt+"非法！");
    }
    
    protected String getValue(String oldValue) throws ExpressionException{
        String reg="^([a-zA-Z0-9_]+)\\(([a-zA-Z0-9_.()]+)\\)$";
        if(this.isFunctionCal(oldValue)){
            Pattern p=Pattern.compile(reg);
            Matcher m=p.matcher(oldValue);
            m.find();
            return calFunction(m.group(1),m.group(2));
        }
        return oldValue;
    }
    
    protected boolean isFunctionCal(String value){
        String reg="^([a-zA-Z0-9_]+)\\(([a-zA-Z0-9_.()]+)\\)$";
        return value.matches(reg);
    }
    
    protected String calFunction(String function,String value) throws ExpressionException{
        String lowerFun=function.toLowerCase();
        double db=0;
        try {
            db=Double.valueOf(this.getValue(value)).doubleValue();
            if(lowerFun.equals("log")){
                return String.valueOf(Math.log(db));
            } else if(lowerFun.equals("square")){
                return String.valueOf(Math.pow(db,2));
            } else if(lowerFun.equals("sqrt")){
                return String.valueOf(Math.sqrt(db));
            } else if(lowerFun.equals("sin")){
                return String.valueOf(Math.sin(db));
            } else if(lowerFun.equals("asin")){
                return String.valueOf(Math.asin(db));
            } else if(lowerFun.equals("cos")){
                return String.valueOf(Math.cos(db));
            } else if(lowerFun.equals("tan")){
                return String.valueOf(Math.tan(db));
            } else if(lowerFun.equals("atan")){
                return String.valueOf(Math.atan(db));
            } else if(lowerFun.equals("ceil")){
                return String.valueOf(Math.ceil(db));
            } else if(lowerFun.equals("exp")){
                return String.valueOf(Math.exp(db));
            }
        }catch(Exception e) {
            throw new ExpressionException("函数"+function+"值"+value+"非法!");
        }
        
        throw new ExpressionException("函数"+function+"不支持！");
    }
    public static void main(String[]args) {
        Eval be=new Eval();
        //String exp="sin(ceil(100))*29+20+30*3+0|0|1+1&1*5+2=2";
        //String exp="sin(ceil(sqrt(100)))*29+20+30*3+0|0|1+1&1*5+2=2";
        String exp="8/(3-8/3)";
        try {
            System.out.println(be.calculate(exp));
        } catch(ExpressionException eE) {
            System.out.println(eE.getMessage());
        }
    }
    
    //表达式异常类代码：
    
    public class ExpressionException extends Exception{
        public ExpressionException(String msg) {
            super(msg);
        }
    }
}