Name: jl125535 Date: 07/13/2004


FULL PRODUCT VERSION :
java version "1.5.0-beta2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-beta2-b51)
Java HotSpot(TM) Client VM (build 1.5.0-beta2-b51, mixed mode, sharing)


EXTRA RELEVANT SYSTEM CONFIGURATION :
not relevant

A DESCRIPTION OF THE PROBLEM :
Method getBigDecimal() in class java.text.DigitList can be optimized. Since Tiger, BigDecimal has constructors that accept char[] arguments, and the new method scaleByPowerOfTen() method.
Instead of

<code>
        StringBuffer temp = new StringBuffer(count + 12);
        temp.append('.');
        temp.append(digits, 0, count);
        temp.append('E');
        temp.append(decimalAt);
        return new BigDecimal(temp.toString());
</code>

use

<code>
        return new BigDecimal(digits, 0, count).scaleByPowerOfTen(decimalAt - count);
</code>

As a result, DecimalFormat will take about 60% time compared to the current implementation.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the test case. The output will show how long parsing takes. Note that the creation of the BigDecimal the old way takes about 85% of the processing time.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Parsing 12345 for 1000000 times took 1250ms.
Using char[] constructor for 1000000 times took 818ms.
Using StringBuffer for 1000000 times took 1760ms.

ACTUAL -
Parsing 12345 for 1000000 times took 2108ms.
Using char[] constructor for 1000000 times took 818ms.
Using StringBuffer for 1000000 times took 1760ms.


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.*;

import java.text.DecimalFormat;
import java.math.BigDecimal;

public class Test {
    
    public static void main(String[] args) {
        // TODO code application logic here
        String value = "12345";
        char[] digits = value.toCharArray();
        int decimalAt = 5;
        int count = digits.length;
        
        int loopCount = 1000000;
        DecimalFormat fmt = new DecimalFormat();
        fmt.setParseBigDecimal(true);
        try {
            BigDecimal d = (BigDecimal) fmt.parse(value);
            long startTime, endTime;
            
            /** The normal usage */
            startTime = System.currentTimeMillis();
            for (int i = 0; i < loopCount; ++i ) {
                d = (BigDecimal) fmt.parse(value);
            }
            endTime = System.currentTimeMillis();
            System.out.println("Parsing " + value + " for " + loopCount
                 + " times took " + (endTime - startTime) + "ms.");
            
            /** The fast way */
            startTime = System.currentTimeMillis();
            for (int i = 0; i < loopCount; ++i ) {
                d = new BigDecimal(digits, 0, count)
                    .scaleByPowerOfTen(decimalAt - count);
            }
            endTime = System.currentTimeMillis();
            System.out.println("Using char[] constructor for " + loopCount
                + " times took " + (endTime - startTime) + "ms.");

            /** The slow way */
            startTime = System.currentTimeMillis();
            for (int i = 0; i < loopCount; ++i ) {
                StringBuffer temp = new StringBuffer(count + 12);
                temp.append('.');
                temp.append(digits, 0, count);
                temp.append('E');
                temp.append(decimalAt);
                d = new BigDecimal(temp.toString());
            }
            endTime = System.currentTimeMillis();
            System.out.println("Using StringBuffer for " + loopCount
                + " times took " + (endTime - startTime) + "ms.");
        } catch (java.text.ParseException e) {
            e.printStackTrace();
        }
    }
}

---------- END SOURCE ----------
(Incident Review ID: 285234)
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###@###.### 10/4/04 03:45 GMT