Retain precision with double in Java

When BigDecimal is your best friend

Although double in Java is faster and needs less memory than BigDecimal, it can exhibit rounding errors due to the way floating-point arithmetic operates. BigDecimal is your secret weapon for scenarios where precision is of utmost importance. These scenarios include:

• Financial operations where even a cent matters
• Scientific calculations calling for maximum precision
• Situations where exactness of decimal numbers is critical

Risky business: Precision loss with double

With double, precision loss can creep in during seemingly harmless operations:

• Simple arithmetic like addition or subtraction can yield small errors that multiply over time.
• Multiplying a teeny-weeny decimal with a gigantic number might throw up strange results.
• Performing division might not only result in non-terminating decimals but also precision errors.

Safeguarding your decimals with BigDecimal

When using BigDecimal, adhere to certain best practices to prevent precision loss:

• Always initiate BigDecimal with a String or BigInteger.
• Avoid combining double and BigDecimal operations to prevent reverting to double's infamous precision.
• If you absolutely must initialize from a double, use BigDecimal.valueOf(double).

Harnessing BigDecimal powers

BigDecimal possesses several attributes that bolster precision control:

• Rounding: You can pick from various rounding modes providing granular control over your results.
• Scaling: You're able to adjust the number of decimals without giving up an inch of precision, thanks to setScale.
• Arithmetic: Perform arithmetic operations confidently without the fear of losing your precious decimal accuracy.

Taking a stance: BigDecimal vs alternatives

If you look beyond BigDecimal, Java offers you a buffet of options: BigInteger for integer arithmetic, and floating-point types (float and double) for scientific arithmetic. See how they compare:

Type	Precision	Use Case
BigDecimal	High	Perfect decimals, sensitive calculations
BigInteger	High	Monster integers
Double	Low	Swift computations, rough approximations

Practical examples

Let's get our hands dirty with some code:

Correct usage of BigDecimal:

BigDecimal a = new BigDecimal("123.456");
BigDecimal b = a.multiply(new BigDecimal("7.89")); // Makes a juicy multiplication
System.out.println(b); // Brings home the bacon without any rounding nightmares
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Incorrect usage of BigDecimal (loses initial precision):

BigDecimal a = new BigDecimal(123.456); // Wrong: Initialized with double, tsk tsk!
BigDecimal b = a.multiply(new BigDecimal("7.89"));
System.out.println(b); // May output a weird result brought to you by rounding errors
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Deep-dive into BigDecimal rounding

You even get to control the rounding behavior:

BigDecimal value = new BigDecimal("123.456789");
value = value.setScale(4, RoundingMode.HALF_UP); // Make it round and shiny.
System.out.println(value); // Outputs "123.4568" dancing lightly on the rounding tightrope!
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