How should you use BigDecimal for money in Java?

Explains decimal construction, scale, equality, rounding, and why BigDecimal needs a money contract around it.

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I use BigDecimal for monetary calculations because it represents decimal values directly instead of approximating them in binary like double. I construct amounts from a decimal string or BigDecimal.valueOf, and arithmetic returns new values because BigDecimal is immutable. Scale and rounding are part of the money contract: an amount may require two fraction digits, while tax or currency conversion may need a documented rounding rule. I would normally enforce those rules in a money value object rather than pass unrestricted BigDecimal values everywhere.

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Practical BigDecimal semantics, deliberate monetary rounding, value equality, and boundary design.

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Overview
The useful answer is not simply to say that BigDecimal is precise; it must explain construction, scale, equality, and where business rounding belongs.
I use BigDecimal for monetary calculations because it represents decimal values directly instead of approximating them in binary like double. I construct amounts from a decimal string or BigDecimal.valueOf, and arithmetic returns new values because BigDecimal is immutable. Scale and rounding are part of the money contract: an amount may require two fraction digits, while tax or currency conversion may need a documented rounding rule. I would normally enforce those rules in a money value object rather than pass unrestricted BigDecimal values everywhere.
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Details

Constructing a BigDecimal directly from a double.
Assuming compareTo and equals use the same equality rule.
Applying an arbitrary rounding mode wherever a calculation fails.
Treating an amount without its currency and scale rules as a complete money type.

How should you use BigDecimal for money in Java?

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