Why Does Converting a Float to a Double Seem to Increase Precision?

Preserving Numerical Precision: Converting Float to Double

When working with primitive data types, ensuring precision is crucial. Converting a float to a double can occasionally introduce unintended rounding errors. Casting a float to double directly may yield unexpected additional precision, as demonstrated in the example:

float temp = 14009.35F;
System.out.println(Float.toString(temp)); // Prints 14009.35
System.out.println(Double.toString((double) temp)); // Prints 14009.349609375

This apparent "extra" precision isn't actually gained during conversion. Instead, the float didn't accurately represent the intended number. The double, on the other hand, reflects the original float's value accurately. When converted to a string, the double reveals the "hidden" data that was present in the float.

Consider this example:

float f = 0.1F;
double d = f;

The value of f might be exactly 0.100000234523. d will possess the same value, but when converted to a string, it will appear with higher precision, displaying the "extra" digits that were already existent.

Converting to a string and back results in a double value closer to the string representation than the original float. However, this is only advantageous if the string value truly represents the intended number.

It's worth considering whether BigDecimal would be a more suitable data type for this scenario. BigDecimal is specifically designed for precise decimal values, ensuring that you work with the exact representation you require.

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