在 java 中将 string 转换为 BigDecimal

我正在将一种货币从 XML读入 Java。

String currency = "135.69";

当我把它转换成 BigDecimal时，我得到:

 System.out.println(new BigDecimal(135.69));

产出:

135.68999999999999772626324556767940521240234375.

为什么它输出这么多数字？我怎样才能避免这种情况呢？我只想让它输出135.69。

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The BigDecimal(double) constructor can have unpredictable behaviors. It is preferable to use BigDecimal(String) or BigDecimal.valueOf(double).

System.out.println(new BigDecimal(135.69)); //135.68999999999999772626324556767940521240234375
System.out.println(new BigDecimal("135.69")); // 135.69
System.out.println(BigDecimal.valueOf(135.69)); // 135.69

The documentation for BigDecimal(double) explains in detail:

  1. The results of this constructor can be somewhat unpredictable. One might assume that writing new BigDecimal(0.1) in Java creates a BigDecimal which is exactly equal to 0.1 (an unscaled value of 1, with a scale of 1), but it is actually equal to 0.1000000000000000055511151231257827021181583404541015625. This is because 0.1 cannot be represented exactly as a double (or, for that matter, as a binary fraction of any finite length). Thus, the value that is being passed in to the constructor is not exactly equal to 0.1, appearances notwithstanding.
  2. The String constructor, on the other hand, is perfectly predictable: writing new BigDecimal("0.1") creates a BigDecimal which is exactly equal to 0.1, as one would expect. Therefore, it is generally recommended that the String constructor be used in preference to this one.
  3. When a double must be used as a source for a BigDecimal, note that this constructor provides an exact conversion; it does not give the same result as converting the double to a String using the Double.toString(double) method and then using the BigDecimal(String) constructor. To get that result, use the static valueOf(double) method.
小开 
String currency = "135.69";
System.out.println(new BigDecimal(currency));


//will print 135.69
小开

May I add something. If you are using currency you should use Scale(2), and you should probably figure out a round method.

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You are storing 135.69 as String in currency. But instead of passing variable currency, you are again passing 135.69(double value) into new BigDecimal(). So you are seeing a lot of numbers in the output. If you pass the currency variable, your output will be 135.69

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Hi Guys you cant convert directly string to bigdecimal

you need to first convert it into long after that u will convert big decimal 

String currency = "135.69";
Long rate1=Long.valueOf((currency ));
System.out.println(BigDecimal.valueOf(rate1));
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BigDecimal b = BigDecimal.valueOf(d);

import java.math.*;


public class Test {


public static void main(String[] args)
{


// Creating a Double Object
Double d = new Double("785.254");


/// Assigning the bigdecimal value of ln to b
BigDecimal b = BigDecimal.valueOf(d);


// Displaying BigDecimal value
System.out.println("The Converted BigDecimal value is: " + b);
}
}
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Spring Framework provides an excellent utils class for achieving this.

Util class : NumberUtils

String to BigDecimal conversion -

NumberUtils.parseNumber("135.00", BigDecimal.class);

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