Why Does Converting a Float to Double Lose Precision, and How Can I Maintain Accuracy?

Maintaining Precision when Converting Float to Double

When converting a primitive float to a primitive double, you may encounter discrepancies in precision due to the inherent nature of floating-point arithmetic. Simply casting the float to double can result in undesired rounding errors, as demonstrated in the provided code:

<code class="java">float temp = 14009.35F;
System.out.println(Float.toString(temp)); // Prints 14009.35
System.out.println(Double.toString((double)temp)); // Prints 14009.349609375</code>

However, converting the float to a string and then parsing it back as a double produces the desired precision:

<code class="java">System.out.println(Double.toString(Double.parseDouble(Float.toString(temp))));
// Prints 14009.35</code>

It's important to note that the seemingly extra precision in the direct cast from float to double is not an actual gain in accuracy. The double representation accurately reflects the inherent precision of the float value. Converting to a string and back simplifies the representation, resulting in a double value closer to the string representation than the original float.

Before relying on this workaround, consider the appropriateness of using float and double data types. If precise decimal values are crucial, as in financial or scientific applications, BigDecimal is recommended as a more suitable type, as it provides greater precision and control over decimal calculations.

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