Android5.0 计算器计算结果不准确和结果末尾的多余的‘0’没有省略的解决方法

Android5.0 计算器计算结果不准确和结果末尾的多余的‘0’没有省略

一、问题的描述：

【测试步骤】

1.进入计算器

2.输入 100-99.9

3.查看计算结果

【测试结果】

1.结果为： 0.0999999999

【预期结果】

1.结果应为： 0.1

【测试步骤】

1.进入计算器

2.输入1000-999.9，查看结果是否为： 0.1

【测试结果】

1.结果显示为： 0.10000000

【预期结果】

1.计算结果小数点后多余的零应该省略。

二、解决方案：path：

<span style="font-size:18px;">package com.android.calculator2;

<span style="color:#ff0000;">import java.util.Locale;//added </span>
import org.javia.arity.Symbols;
import org.javia.arity.SyntaxException;
import org.javia.arity.Util;

public class CalculatorExpressionEvaluator {

    private static final int MAX_DIGITS = 12;
    private static final int ROUNDING_DIGITS = 2;

    private final Symbols mSymbols;
    private final CalculatorExpressionTokenizer mTokenizer;

    <span style="color:#ff0000;">private static final String NAN      = "NaN";//added</span>
    public CalculatorExpressionEvaluator(CalculatorExpressionTokenizer tokenizer) {
        mSymbols = new Symbols();
        mTokenizer = tokenizer;
    }

    public void evaluate(CharSequence expr, EvaluateCallback callback) {
        evaluate(expr.toString(), callback);
    }

    public void evaluate(String expr, EvaluateCallback callback) {
        expr = mTokenizer.getNormalizedExpression(expr);

        // remove any trailing operators
        while (expr.length() > 0 && "+-/*".indexOf(expr.charAt(expr.length() - 1)) != -1) {
            expr = expr.substring(0, expr.length() - 1);
        }

        try {
            if (expr.length() == 0 || Double.valueOf(expr) != null) {
                callback.onEvaluate(expr, null, Calculator.INVALID_RES_ID);
                return;
            }
        } catch (NumberFormatException e) {
            // expr is not a simple number
        }

        try {
            double result = mSymbols.eval(expr);
            if (Double.isNaN(result)) {
                callback.onEvaluate(expr, null, R.string.error_nan);
            } else {
                // The arity library uses floating point arithmetic when evaluating the expression
                // leading to precision errors in the result. The method doubleToString hides these
                // errors; rounding the result by dropping N digits of precision.
            	<span style="color:#ff0000;">/*add*/
            	String strResult = "";
                for (int precision = MAX_DIGITS; precision > 6; precision--) {
                	strResult = tryFormattingWithPrecision(result, precision);
                    if (strResult.length() <= MAX_DIGITS) {
                        break;
                    }
                }
                /*end*/</span>
              <span style="color:#ff0000;">  final String resultString = mTokenizer.getLocalizedExpression(
                        /*Util.doubleToString(result, MAX_DIGITS, ROUNDING_DIGITS)*/strResult);//modified</span>
                callback.onEvaluate(expr, resultString, Calculator.INVALID_RES_ID);
            }
        } catch (SyntaxException e) {
            callback.onEvaluate(expr, null, R.string.error_syntax);
        }
    }

    public interface EvaluateCallback {
        public void onEvaluate(String expr, String result, int errorResourceId);
    }</span>

<span style="font-size:18px;">
<span style="color:#ff0000;">    /*added*/

    private String tryFormattingWithPrecision(double value, int precision) {
        // The standard scientific formatter is basically what we need. We will
        // start with what it produces and then massage it a bit.
        String result = String.format(Locale.US, "%" + MAX_DIGITS + "." + precision + "g", value);
        if (result.equals(NAN)) { // treat NaN as Error
            return "NAN";
        }

        String mantissa = result;
        String exponent = null;
        int e = result.indexOf('e');
        if (e != -1) {
            mantissa = result.substring(0, e);

            // Strip "+" and unnecessary 0's from the exponent
            exponent = result.substring(e + 1);
            if (exponent.startsWith("+")) {
                exponent = exponent.substring(1);
            }
            exponent = String.valueOf(Integer.parseInt(exponent));
        } else {
            mantissa = result;
        }

        int period = mantissa.indexOf('.');
        if (period == -1) {
            period = mantissa.indexOf(',');
        }
        if (period != -1) {
            // Strip trailing 0's
            while (mantissa.length() > 0 && mantissa.endsWith("0")) {
                mantissa = mantissa.substring(0, mantissa.length() - 1);
            }
            if (mantissa.length() == period + 1) {
                mantissa = mantissa.substring(0, mantissa.length() - 1);
            }
        }

        if (exponent != null) {
            result = mantissa + 'e' + exponent;
        } else {
            result = mantissa;
        }
        return result;
    }
    /*end*/</span>
}</span>