blocks|key|2562812|text|1)请勿使用double。浮点逻辑充其量是近似的。请改用BigDecimal。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2562813|2)我认为BigDecimal已经有了一种设置精度的方法。如果不是，只需乘以1000和trunc即可。执行该操作，获得一个新的数字，并与原始数字进行比较。如果不同，则失败。|2562814|entityMap^0|6|6|S|A|0|5|A|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|R|8|@]|D|@]|E|$]]]|I|$]]

1) Do not use <code>double</code>. Floating point logic is approximated at best. Use <code>BigDecimal</code> instead.

2) I think <code>BigDecimal</code> already has a way of setting a precision. If not, just multiply by 1000 and trunc. Do the operation, get a new number, and compare to the original one. If it is different, fail.

blocks|key|2562847|text|这将通过您的测试：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2562848|package+com.sandbox;

import+org.junit.Test;

import+static+junit.framework.Assert.assertFalse;
import+static+junit.framework.Assert.assertTrue;

public+class+SandboxTest+{


++++@Test
++++public+void+testPrecision()+{
++++++++assertFalse(precisionLessThanOrEqualTo3(20.44567567));
++++++++assertTrue(precisionLessThanOrEqualTo3(20.444));
++++++++assertTrue(precisionLessThanOrEqualTo3(20.1));
++++++++assertTrue(precisionLessThanOrEqualTo3(20));
++++}

++++private+boolean+precisionLessThanOrEqualTo3(double+x)+{
++++++++return+String.valueOf(x).replaceAll(".*\\.",+"").length()+<=+3;
++++}
}|code-block|syntax|javascript|2562849|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This passes your tests:

<pre><code>package com.sandbox;

import org.junit.Test;

import static junit.framework.Assert.assertFalse;
import static junit.framework.Assert.assertTrue;

public class SandboxTest {


 @Test
 public void testPrecision() {
 assertFalse(precisionLessThanOrEqualTo3(20.44567567));
 assertTrue(precisionLessThanOrEqualTo3(20.444));
 assertTrue(precisionLessThanOrEqualTo3(20.1));
 assertTrue(precisionLessThanOrEqualTo3(20));
 }

 private boolean precisionLessThanOrEqualTo3(double x) {
 return String.valueOf(x).replaceAll(".*\\.", "").length() &lt;= 3;
 }
}
</code></pre>

blocks|key|438405|text|您可以使用以下代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|438406|boolean+f+(double+in){
++++if+(in*1000+>+(float)(int)(in*1000))
++++++++return+false;
++++return+true;
}|code-block|syntax|javascript|438407|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can use the following code:

<pre><code>boolean f (double in){
 if (in*1000 &gt; (float)(int)(in*1000))
 return false;
 return true;
}
</code></pre>

blocks|key|1045467|text|对术语"precision"有多种可能的解释|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1045468|1045469|算术精度是有效数字(小数点前后)的总数。|unordered-list-item|1045470|小数部分的位数(或小数位数在数据库中，精度可以用计数中包含的固定小数位数(小数位数)来衡量，因此NUMBER(6,2)列将存储最多6位的数字，这些数字始终由2个小数位和4个整数位组成。|style|CODE|1045471|1045472|在您的示例中，您似乎将精度度量为最大小数位数。|1045473|其中的每一个都可以使用以下命令进行测试：|1045474|import+java.math.BigDecimal;

import+org.junit.Test;
import+static+org.junit.Assert.*;


public+class+Precision
{
++/**
+++*+Tests+to+see+whether+the+number+has+up+to+the+given+number+of
+++*+decimal+places.
+++*+
+++*+@param+value+The+value+to+test.
+++*+@param+scale+The+maximum+number+of+decimal+places.+
+++*+@return++++++<code>true</code>+if+the+value+has+up+to+the
+++*++++++++++++++expected+number+of+decimal+places.
+++*/
++static+final+boolean+hasDecimalPlaces(
++++++final+double+value,
++++++final+int++++scale
++)
++{
++++try
++++{
++++++new+BigDecimal(+Double.toString(+value+)+).setScale(+scale+);
++++++return+true;
++++}
++++catch+(+final+ArithmeticException+ex+)
++++{
++++++return+false;
++++}
++}

++/**
+++*+Tests+to+see+whether+the+number+has+up+to+the+given+number+of
+++*+significant+figures.
+++*+
+++*+@param+value+++++The+value+to+test.
+++*+@param+precision+The+maximum+number+of+significant+figures+to
+++*++++++++++++++++++test+for.
+++*+@return++++++++++<code>true</code>+if+the+value+has+up+to+the
+++*++++++++++++++++++expected+number+of+significant+figures.+
+++*/
++static+final+boolean+hasSignificantFigures(
++++++final+double+value,
++++++final+int++++precision
++)
++{
++++try
++++{
++++++return+new+BigDecimal(+Double.toString(+value+)+).stripTrailingZeros().precision()+<=+precision;
++++}
++++catch+(+final+ArithmeticException+ex+)
++++{
++++++return+false;
++++}
++}

++/**
+++*+Tests+to+see+whether+the+number+has+at+most+the+given+number+of
+++*+decimal+places+and,+when+represented+at+that+maximum+number+of
+++*+decimal+places,+has+up+to+the+given+number+of+digits.
+++*+
+++*+@param+value+++++The+number+to+test.
+++*+@param+precision+The+maximum+number+of+digits+to+test+for.
+++*+@param+scale+++++The+maximum+number+of+decimal+places.
+++*+@return++++++++++<code>true</code>+if+the+value+can+be+represented
+++*++++++++++++++++++at+the+given+scale+and,+at+that+scale,+is+up+to
+++*++++++++++++++++++the+given+precision.
+++*/
++static+final+boolean+hasDigitsAtScale(
++++++final+double+value,
++++++final+int++++precision,
++++++final+int++++scale
++)
++{
++++try
++++{
++++++return+new+BigDecimal(+Double.toString(+value+)+).setScale(+scale+).precision()+<=+precision;
++++}
++++catch+(+final+ArithmeticException+ex+)
++++{
++++++return+false;
++++}
++}

++@Test
++public+void+testScale(){
++++assertTrue(+hasDecimalPlaces(+20d,+3+)+);
++++assertTrue(+hasDecimalPlaces(+20.123d,+3+)+);
++++assertFalse(+hasDecimalPlaces(+20.1234d,+3+)+);
++}

++@Test
++public+void+testPrecision(){
++++assertTrue(++hasSignificantFigures(++++20d,++++++3+)+);
++++assertTrue(++hasSignificantFigures(+++120d,++++++3+)+);
++++assertTrue(++hasSignificantFigures(++1230d,++++++3+)+);
++++assertFalse(+hasSignificantFigures(+12340d,++++++3+)+);
++++assertTrue(++hasSignificantFigures(++++20.1d,++++3+)+);
++++assertFalse(+hasSignificantFigures(++++20.12d,+++3+)+);
++++assertTrue(++hasSignificantFigures(+++++0.123d,++3+)+);
++++assertFalse(+hasSignificantFigures(+++++0.1234d,+3+)+);
++++assertTrue(++hasSignificantFigures(+++++0.0000999d,++3+)+);
++++assertFalse(+hasSignificantFigures(+++++0.00009999d,+3+)+);
++}

++@Test
++public+void+testPrecisionAndScale(){
++++assertTrue(++hasDigitsAtScale(+++++0d,++++++3,+0+)+);
++++assertFalse(+hasDigitsAtScale(+++++0.01d,+++3,+0+)+);
++++assertFalse(+hasDigitsAtScale(+++++0.1d,++++3,+0+)+);
++++assertTrue(++hasDigitsAtScale(+++++1d,++++++3,+0+)+);
++++assertTrue(++hasDigitsAtScale(++++10d,++++++3,+0+)+);
++++assertTrue(++hasDigitsAtScale(+++100d,++++++3,+0+)+);
++++assertFalse(+hasDigitsAtScale(++1000d,++++++3,+0+)+);
++++assertFalse(+hasDigitsAtScale(+10000d,++++++3,+0+)+);

++++assertTrue(++hasDigitsAtScale(+++++0d,++++++3,+1+)+);
++++assertFalse(+hasDigitsAtScale(+++++0.01d,+++3,+1+)+);
++++assertTrue(++hasDigitsAtScale(+++++0.1d,++++3,+1+)+);
++++assertTrue(++hasDigitsAtScale(+++++1d,++++++3,+1+)+);
++++assertTrue(++hasDigitsAtScale(++++10d,++++++3,+1+)+);
++++assertFalse(+hasDigitsAtScale(+++100d,++++++3,+1+)+);
++++assertFalse(+hasDigitsAtScale(++1000d,++++++3,+1+)+);
++++assertFalse(+hasDigitsAtScale(+10000d,++++++3,+1+)+);

++++assertTrue(++hasDigitsAtScale(+++++0d,++++++3,+-1+)+);
++++assertFalse(+hasDigitsAtScale(+++++0.01d,+++3,+-1+)+);
++++assertFalse(+hasDigitsAtScale(+++++0.1d,++++3,+-1+)+);
++++assertFalse(+hasDigitsAtScale(+++++1d,++++++3,+-1+)+);
++++assertTrue(++hasDigitsAtScale(++++10d,++++++3,+-1+)+);
++++assertTrue(++hasDigitsAtScale(+++100d,++++++3,+-1+)+);
++++assertTrue(++hasDigitsAtScale(++1000d,++++++3,+-1+)+);
++++assertFalse(+hasDigitsAtScale(+10000d,++++++3,+-1+)+);
++}
}|code-block|syntax|javascript|1045475|entityMap|0|LINK|mutability|MUTABLE|url|https://simple.wikipedia.org/wiki/Arithmetic_precision^0|3|B|0|0|0|0|1C|B|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@]|9|@$A|14|B|15|1|16]]|C|$]]|$1|D|3|-4|5|6|7|17|8|@]|9|@]|C|$]]|$1|E|3|F|5|G|7|18|8|@]|9|@]|C|$]]|$1|H|3|I|5|G|7|19|8|@$A|1A|B|1B|J|K]]|9|@]|C|$]]|$1|L|3|-4|5|6|7|1C|8|@]|9|@]|C|$]]|$1|M|3|N|5|6|7|1D|8|@]|9|@]|C|$]]|$1|O|3|P|5|6|7|1E|8|@]|9|@]|C|$]]|$1|Q|3|R|5|S|7|1F|8|@]|9|@]|C|$T|U]]|$1|V|3|-4|5|6|7|1G|8|@]|9|@]|C|$]]]|W|$X|$5|Y|Z|10|C|$11|12]]]]

There are multiple possible interpretations of the term <a href="https://simple.wikipedia.org/wiki/Arithmetic_precision" rel="nofollow noreferrer">"precision"</a>:

<ul>
<li>The arithmetic precision is the total number of significant figures (before and after the decimal point).</li>
<li>The number of digits in the fractional part of the number (or the number of decimal places).</li>
<li>Particularly in databases, precision can be measured with a fixed number of decimal places (the scale) included in the count so a <code>NUMBER(6,2)</code> column would store numbers that have at most 6 digits which is always composed of 2 decimal places and 4 integer digits.</li>
</ul>

For your examples, you appear to be measuring precision as the maximum number of decimal places.

Each of these can be tested using:

<pre><code>import java.math.BigDecimal;

import org.junit.Test;
import static org.junit.Assert.*;


public class Precision
{
 /**
 * Tests to see whether the number has up to the given number of
 * decimal places.
 * 
 * @param value The value to test.
 * @param scale The maximum number of decimal places. 
 * @return &lt;code&gt;true&lt;/code&gt; if the value has up to the
 * expected number of decimal places.
 */
 static final boolean hasDecimalPlaces(
 final double value,
 final int scale
 )
 {
 try
 {
 new BigDecimal( Double.toString( value ) ).setScale( scale );
 return true;
 }
 catch ( final ArithmeticException ex )
 {
 return false;
 }
 }

 /**
 * Tests to see whether the number has up to the given number of
 * significant figures.
 * 
 * @param value The value to test.
 * @param precision The maximum number of significant figures to
 * test for.
 * @return &lt;code&gt;true&lt;/code&gt; if the value has up to the
 * expected number of significant figures. 
 */
 static final boolean hasSignificantFigures(
 final double value,
 final int precision
 )
 {
 try
 {
 return new BigDecimal( Double.toString( value ) ).stripTrailingZeros().precision() &lt;= precision;
 }
 catch ( final ArithmeticException ex )
 {
 return false;
 }
 }

 /**
 * Tests to see whether the number has at most the given number of
 * decimal places and, when represented at that maximum number of
 * decimal places, has up to the given number of digits.
 * 
 * @param value The number to test.
 * @param precision The maximum number of digits to test for.
 * @param scale The maximum number of decimal places.
 * @return &lt;code&gt;true&lt;/code&gt; if the value can be represented
 * at the given scale and, at that scale, is up to
 * the given precision.
 */
 static final boolean hasDigitsAtScale(
 final double value,
 final int precision,
 final int scale
 )
 {
 try
 {
 return new BigDecimal( Double.toString( value ) ).setScale( scale ).precision() &lt;= precision;
 }
 catch ( final ArithmeticException ex )
 {
 return false;
 }
 }

 @Test
 public void testScale(){
 assertTrue( hasDecimalPlaces( 20d, 3 ) );
 assertTrue( hasDecimalPlaces( 20.123d, 3 ) );
 assertFalse( hasDecimalPlaces( 20.1234d, 3 ) );
 }

 @Test
 public void testPrecision(){
 assertTrue( hasSignificantFigures( 20d, 3 ) );
 assertTrue( hasSignificantFigures( 120d, 3 ) );
 assertTrue( hasSignificantFigures( 1230d, 3 ) );
 assertFalse( hasSignificantFigures( 12340d, 3 ) );
 assertTrue( hasSignificantFigures( 20.1d, 3 ) );
 assertFalse( hasSignificantFigures( 20.12d, 3 ) );
 assertTrue( hasSignificantFigures( 0.123d, 3 ) );
 assertFalse( hasSignificantFigures( 0.1234d, 3 ) );
 assertTrue( hasSignificantFigures( 0.0000999d, 3 ) );
 assertFalse( hasSignificantFigures( 0.00009999d, 3 ) );
 }

 @Test
 public void testPrecisionAndScale(){
 assertTrue( hasDigitsAtScale( 0d, 3, 0 ) );
 assertFalse( hasDigitsAtScale( 0.01d, 3, 0 ) );
 assertFalse( hasDigitsAtScale( 0.1d, 3, 0 ) );
 assertTrue( hasDigitsAtScale( 1d, 3, 0 ) );
 assertTrue( hasDigitsAtScale( 10d, 3, 0 ) );
 assertTrue( hasDigitsAtScale( 100d, 3, 0 ) );
 assertFalse( hasDigitsAtScale( 1000d, 3, 0 ) );
 assertFalse( hasDigitsAtScale( 10000d, 3, 0 ) );

 assertTrue( hasDigitsAtScale( 0d, 3, 1 ) );
 assertFalse( hasDigitsAtScale( 0.01d, 3, 1 ) );
 assertTrue( hasDigitsAtScale( 0.1d, 3, 1 ) );
 assertTrue( hasDigitsAtScale( 1d, 3, 1 ) );
 assertTrue( hasDigitsAtScale( 10d, 3, 1 ) );
 assertFalse( hasDigitsAtScale( 100d, 3, 1 ) );
 assertFalse( hasDigitsAtScale( 1000d, 3, 1 ) );
 assertFalse( hasDigitsAtScale( 10000d, 3, 1 ) );

 assertTrue( hasDigitsAtScale( 0d, 3, -1 ) );
 assertFalse( hasDigitsAtScale( 0.01d, 3, -1 ) );
 assertFalse( hasDigitsAtScale( 0.1d, 3, -1 ) );
 assertFalse( hasDigitsAtScale( 1d, 3, -1 ) );
 assertTrue( hasDigitsAtScale( 10d, 3, -1 ) );
 assertTrue( hasDigitsAtScale( 100d, 3, -1 ) );
 assertTrue( hasDigitsAtScale( 1000d, 3, -1 ) );
 assertFalse( hasDigitsAtScale( 10000d, 3, -1 ) );
 }
}
</code></pre>

I would like to test a double for a maximum percision of 3 or less. What is the best way to do this in Java?

<pre><code>20.44567567 &lt;- Fail
20.444 &lt;- Pass
20.1 &lt;- Pass
20 &lt;- Pass
</code></pre>

Test Number For Maximum Precision In Java

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我想测试最大精度为3或更低的双精度。在Java中实现这一点的最佳方法是什么？20.44567567 <- Fail20.444 <- Pass20.1 <- Pass20 <- Pass

问Java中最大精度的测试号
EN

回答 4

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