Why does BigDecimal divide cause rounding when it should fit within the significant digits?

Why does BigDecimal divide cause rounding to happen even though the value should fit comfortably in 4 significant digits?

BigDecimal realPercent = new BigDecimal(1.25, new MathContext(4));
// 1.25
BigDecimal percentDivider = new BigDecimal(100, new MathContext(4));
realPercent = realPercent.divide(percentDivider, BigDecimal.ROUND_HALF_UP);
// 0.01

It's possible to make divide behave like I want by setting the precision on the method call, but it doesn't explain why it doesn't already do it.

realPercent.divide(percentDivider, 4, BigDecimal.ROUND_HALF_UP)
// 0.0125
Jon Skeet
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From the Javadoc of divide(BigDecimal, RoundingMode):

Returns a BigDecimal whose value is (this / divisor), and whose scale is this.scale()

The last part is important - the scale of your initial value is 2 (the unscaled value is 125). Because you've called an overload that pins the scale, the closest result available is scale=2, unscaled=1, i.e. 0.01.

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