ADDITIONAL SYSTEM INFORMATION :
Property settings:
    file.encoding = UTF-8
    file.separator = /
    java.class.path =
    java.class.version = 69.0
    java.home = /home/user/.sdkman/candidates/java/25.0.1-tem
    java.io.tmpdir = /tmp
    java.library.path = /usr/java/packages/lib
        /usr/lib64
        /lib64
        /lib
        /usr/lib
    java.runtime.name = OpenJDK Runtime Environment
    java.runtime.version = 25.0.1+8-LTS
    java.specification.name = Java Platform API Specification
    java.specification.vendor = Oracle Corporation
    java.specification.version = 25
    java.vendor = Eclipse Adoptium
    java.vendor.url = https://adoptium.net/
    java.vendor.url.bug = https://github.com/adoptium/adoptium-support/issues
    java.vendor.version = Temurin-25.0.1+8
    java.version = 25.0.1
    java.version.date = 2025-10-21
    java.vm.compressedOopsMode = Zero based
    java.vm.info = mixed mode, sharing
    java.vm.name = OpenJDK 64-Bit Server VM
    java.vm.specification.name = Java Virtual Machine Specification
    java.vm.specification.vendor = Oracle Corporation
    java.vm.specification.version = 25
    java.vm.vendor = Eclipse Adoptium
    java.vm.version = 25.0.1+8-LTS
    jdk.debug = release
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    os.arch = amd64
    os.name = Linux
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    stderr.encoding = UTF-8
    stdin.encoding = UTF-8
    stdout.encoding = UTF-8
    sun.arch.data.model = 64
    sun.boot.library.path = /home/user/.sdkman/candidates/java/25.0.1-tem/lib
    sun.cpu.endian = little
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    sun.management.compiler = HotSpot 64-Bit Tiered Compilers

openjdk version "25.0.1" 2025-10-21 LTS
OpenJDK Runtime Environment Temurin-25.0.1+8 (build 25.0.1+8-LTS)
OpenJDK 64-Bit Server VM Temurin-25.0.1+8 (build 25.0.1+8-LTS, mixed mode, sharing)

A DESCRIPTION OF THE PROBLEM :
When using DecimalFormat to format a BigDecimal with value 0.50 it returns 0 instead of 1. I will try to explain how the code behaves:

When DecimalFormat.format() is called the DigitList.set() is called. DigitList sets the value count to 2 (there are 2 digits), digits array to [5, 0, �, �, �, �, �, �, �, �, �, �, �, �, �, �, �, �, �], decimalAt to 0. This triggers the if statement that should decide to round up:
if (shouldRoundUp(0, roundedUp, valueExactAsDecimal))

Instead of true the shouldRoundUp method returns false.

The shouldRoundUp method enters the switch statement with HALF_UP and digits[maximumDigits] == 5 true.

below if statement is false because maximum digits is not equal to count -1 (0 == 1 is false)
// Rounding position is the last index, there are 3 Cases.
if (maximumDigits == (count - 1)) {}

the else statement goes to the to nonZeroAfterIndex(maximumDigits+1). This checks if there's any non zeros in the digits array. This is also false because it starts from index 1 which is the 0 and there are no other digits.

The conclusion of shouldRoundUp is false which is incorrect

REGRESSION : Last worked in version 21.0.9

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
DecimalFormat decimalFormat = new DecimalFormat(); decimalFormat.setMaximumFractionDigits(0); decimalFormat.setRoundingMode(RoundingMode.HALF_UP);
BigDecimal value = new BigDecimal("0.50");
String shouldBeOne = decimalFormat.format(value);
assertThat(shouldBeOne, is("1"));

---------- BEGIN SOURCE ----------
@Test
void decimalFormatTest() {
DecimalFormat decimalFormat = new DecimalFormat(); decimalFormat.setMaximumFractionDigits(0); decimalFormat.setRoundingMode(RoundingMode.HALF_UP);
BigDecimal value = new BigDecimal("0.50");
String shouldBeOne = decimalFormat.format(value);
assertThat(shouldBeOne, is("1"));
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
create an if statement to check if the BigDecimal to format is equal to new BigDecimal("0.50"). if true call the formatter with value.setScale(1, HALF_UP)

FREQUENCY :
ALWAYS