This Heads-Up is part of the regular communication sent to the projects involved; it covers that java.text.DecimalFormat formats floating-point values with the Double.toString(double) algorithm.

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JDK 26 changes DecimalFormat to use the same floating-point formatting algorithm as Double.toString() and Formatter, which was enhanced in JDK 21. This fixes inconsistencies where DecimalFormat and Formatter produced different outputs for certain double values. A compatibility flag (-Djdk.compat.DecimalFormat=true) temporarily enables the old algorithm to help with migration. Developers should test with JDK 26 Early Access builds to identify any impacts.

JDK 26: DecimalFormat Uses the Double.toString(double) Algorithm – Inside.java

DecimalFormat Formats Floating-Point Values with the Double.toString(double) Algorithm