Bigdecimal from double

Summary

• Rule ID: BIGDECIMAL_FROM_DOUBLE
• Name: BigDecimal from double
• Description: Reports BigDecimal constructor calls that take double because they can introduce precision surprises.
• Annotation policy: @Suppress/@SuppressWarnings are not supported; only JSpecify annotations are recognized for annotation-driven semantics, and non-JSpecify annotations do not change behavior.

Motivation

Using new BigDecimal(double) captures binary floating-point approximation instead of the intended decimal value. This can cause subtle rounding and comparison bugs in financial or precision-sensitive code.

What it detects

• Constructor calls to java/math/BigDecimal.<init>(D)V.
• Constructor calls to java/math/BigDecimal.<init>(DLjava/math/MathContext;)V.
• Findings on analysis-target classes only.

What it does NOT detect

• BigDecimal.valueOf(double) calls.
• String-based constructors such as new BigDecimal("0.1").
• Suppression via annotations (@Suppress, @SuppressWarnings) is not supported.
• Non-JSpecify annotations do not affect rule behavior.

Examples (TP/TN/Edge)

True Positive

import java.math.BigDecimal;

class ClassA {
    BigDecimal MethodX() {
        return new BigDecimal(0.1d);
    }
}

True Negative

import java.math.BigDecimal;

class ClassB {
    BigDecimal MethodY() {
        return BigDecimal.valueOf(0.1d);
    }
}

Edge Case

import java.math.BigDecimal;
import java.math.MathContext;

class ClassC {
    BigDecimal MethodZ(double varOne) {
        return new BigDecimal(varOne, MathContext.DECIMAL64);
    }
}

Output

• Message: "BigDecimal constructed from double can lose precision. Use BigDecimal.valueOf(double) or a decimal string constructor."
• Location: the BigDecimal constructor call site.

Performance considerations

• Expected linear scan over extracted call sites per method.
• No control-flow fixpoint analysis is required.

Acceptance criteria

• Reports a finding for each BigDecimal constructor call that accepts double.
• Does not report BigDecimal.valueOf(double) or string constructors.
• Emits the actionable message defined in Output.
• Applies only to analysis-target classes.
• Applies annotation policy exactly as stated in Summary.