java 计算器 的实现

java 代码

import java.math.BigDecimal;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Stack;
import java.util.StringTokenizer;

public class Expression {

    public static void main(String[] args) {

        String expres = "c*d+(((a+67.32)+(c-39))/d+10)";
//      expres = "11*13+(((13+67.32)+(13-39))/56+23)";

        HashMap variables = new HashMap();
        variables.put("a",new BigDecimal("10"));
        variables.put("b",new BigDecimal("20"));
        variables.put("c",new BigDecimal("30"));
        variables.put("d",new BigDecimal("40"));

        Expression calc = new Expression(variables,expres);
//      calc = new Ccl(null,expres);

        double resut = calc.getResult().doubleValue();
        System.out.println(" Expression = "+expres);
        calc.printVariables();
        System.out.println(" Result = " + resut);

    }


    //----------
    private String expression;
    private HashMap operators = new HashMap();
    {
        operators.put("+", "1");
        operators.put("-", "1");
        operators.put("/", "2");
        operators.put("*", "2");
        operators.put("(", "0");
    }
    private Context ctx;


    public Expression(HashMap vars,String expr) {
        ctx = new Context(vars);
        expression = expr;
    }

    public BigDecimal getResult() {

        //infix to Postfix
        String pfExpr = infixToPostFix(toVaviable(expression));

        //build the Binary Tree
        Expressions rootNode = buildTree(pfExpr);

        //Evaluate the tree
        return rootNode.evaluate(ctx).setScale(2,BigDecimal.ROUND_HALF_UP);

    }

    private NonTerminalExpression getNonTerminalExpression(
        String operation,
        Expressions l,
        Expressions r) {
        if (operation.trim().equals("+")) {
            return new AddExpression(l, r);
        }
        if (operation.trim().equals("-")) {
            return new SubtractExpression(l, r);
        }
        if (operation.trim().equals("*")) {
            return new MultiplyExpression(l, r);
        }
        if (operation.trim().equals("/")) {
            return new DivExpression(l, r);
        }
        return null;
    }



    private String toVaviable(String str){
        char var = 'z';
        StringBuffer tmp = new StringBuffer();

        StringTokenizer st = new StringTokenizer(str, "+-*/()", true);
        String ss = null;
        while (st.hasMoreElements()) {
            ss = st.nextToken();

            if(isDigital(ss)){
                ctx.assign((var)+"",ss);
                tmp.append((var)+"");
                var--;
            }else{
                tmp.append(ss);
            }
//          System.out.println(ss);
        }

        return tmp.toString();
    }

    private String infixToPostFix(String str) {
        Stack s = new Stack();
        String pfExpr = "";
        String tempStr = "";

        String expr = str.trim();
        for (int i = 0; i < str.length(); i++) {

            String currChar = str.substring(i, i + 1);

            if ((isOperator(currChar) == false)
                && (!currChar.equals("("))
                && (!currChar.equals(")"))) {
                pfExpr = pfExpr + currChar;
            }
            if (currChar.equals("(")) {
                s.push(currChar);
            }
            //for ')' pop all stack contents until '('
            if (currChar.equals(")")) {
                tempStr = (String) s.pop();
                while (!tempStr.equals("(")) {
                    pfExpr = pfExpr + tempStr;
                    tempStr = (String) s.pop();
                }
                tempStr = "";
            }
            //if the current character is an
            // operator
            if (isOperator(currChar)) {
                if (s.isEmpty() == false) {
                    tempStr = (String) s.pop();
                    String strVal1 = (String) operators.get(tempStr);
                    int val1 = new Integer(strVal1).intValue();
                    String strVal2 = (String) operators.get(currChar);
                    int val2 = new Integer(strVal2).intValue();

                    while ((val1 >= val2)) {
                        pfExpr = pfExpr + tempStr;
                        val1 = -100;
                        if (s.isEmpty() == false) {
                            tempStr = (String) s.pop();
                            strVal1 = (String) operators.get(tempStr);
                            val1 = new Integer(strVal1).intValue();

                        }
                    }
                    if ((val1 < val2) && (val1 != -100))
                        s.push(tempStr);
                }
                s.push(currChar);
            } //if

        } // for

        while (s.isEmpty() == false) {
            tempStr = (String) s.pop();
            pfExpr = pfExpr + tempStr;
        }

        return pfExpr;
    }

    private Expressions buildTree(String expr) {
        Stack s = new Stack();

        for (int i = 0; i < expr.length(); i++) {
            String currChar = expr.substring(i, i + 1);

            if (isOperator(currChar) == false) {
                Expressions e = new TerminalExpression(currChar);
                s.push(e);
            } else {
                Expressions r = (Expressions) s.pop();
                Expressions l = (Expressions) s.pop();
                Expressions n = getNonTerminalExpression(currChar, l, r);
                s.push(n);
            }
        } //for
        return (Expressions) s.pop();
    }

    private boolean isDigital(String str) {
        if (!isOperator(str) && !ctx.checkKey(str) && !isComma(str))
            return true;
        return false;
    }

    private boolean isComma(String str) {
        if ((str.equals("("))
            || (str.equals(")")))
            return true;
        return false;
    }

    private boolean isOperator(String str) {
        if ((str.equals("+"))
            || (str.equals("-"))
            || (str.equals("*"))
            || (str.equals("/")))
            return true;
        return false;
    }

    public void printVariables(){
        this.ctx.print();
    }
} // End of class

class Context {

    private HashMap varList = new HashMap();

    public void assign(String var, String value) {
        varList.put(var, new BigDecimal(value));
    }

    public BigDecimal getValue(String var) {
        BigDecimal  tmp;
        if(varList.get(var) == null){
            tmp = new BigDecimal(var);
        }else{
            tmp = (BigDecimal) varList.get(var);
        }

//      System.out.println(var+ " "+tmp.doubleValue());

        return tmp;
    }

    public boolean checkKey(String var){

        return varList.get(var) == null?false:true;

    }
    public void print(){
        Object ob ;
        for(Iterator it = varList.keySet().iterator();it.hasNext();){
            ob = it.next();
            System.out.println(ob+" = "+varList.get(ob));
        }
    }

    public Context(HashMap vars) {
        if(vars !=null)
            varList = vars;
    }

}


class TerminalExpression implements Expressions {

    private String var;

    public TerminalExpression(String v) {
        var = v;
    }

    public BigDecimal evaluate(Context c) {
        return c.getValue(var);
    }
}


interface Expressions {
    public BigDecimal evaluate(Context c);
}



abstract class NonTerminalExpression implements Expressions {
    private Expressions leftNode;

    private Expressions rightNode;

    public NonTerminalExpression(Expressions l, Expressions r) {
        setLeftNode(l);
        setRightNode(r);
    }

    public void setLeftNode(Expressions node) {
        leftNode = node;
    }

    public void setRightNode(Expressions node) {
        rightNode = node;
    }

    public Expressions getLeftNode() {
        return leftNode;
    }

    public Expressions getRightNode() {
        return rightNode;
    }
} // NonTerminalExpression



class AddExpression extends NonTerminalExpression {
    public BigDecimal evaluate(Context c) {
        return getLeftNode().evaluate(c).add(getRightNode().evaluate(c));
    }

    public AddExpression(Expressions l, Expressions r) {
        super(l, r);
    }
} // AddExpression



class SubtractExpression extends NonTerminalExpression {
    public BigDecimal evaluate(Context c) {
        return getLeftNode().evaluate(c).subtract(getRightNode().evaluate(c));
    }

    public SubtractExpression(Expressions l, Expressions r) {
        super(l, r);
    }
} // SubtractExpression



class MultiplyExpression extends NonTerminalExpression {
    public BigDecimal evaluate(Context c) {
        return getLeftNode().evaluate(c).multiply(getRightNode().evaluate(c));
    }

    public MultiplyExpression(Expressions l, Expressions r) {
        super(l, r);
    }
} //



class DivExpression extends NonTerminalExpression {
    public BigDecimal evaluate(Context c) {
        return getLeftNode().evaluate(c).divide(getRightNode().evaluate(c),4,BigDecimal.ROUND_HALF_UP);
    }

    public DivExpression(Expressions l, Expressions r) {
        super(l, r);
    }

} //

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• 2007-10-12 17:39
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1 楼 yezeguo 2009-09-21  

原来是在处理表达式，我以为是在做计算器