test/jdk/java/util/Formatter/BigDecimalRounding.java

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/**
 * @test
 * @bug 8262744
 * @summary BigDecimal does not always display formatting correctly because
 * rounding is done after formatting check. Fix moves rounding to before the
 * range-based formatting check for %g formatting flag.
 * @run testng BigDecimalRounding
 */

import org.testng.annotations.Test;

import java.math.BigDecimal;

import static org.testng.Assert.*;

@Test
public class BigDecimalRounding {

    public static void testBigDecimalRounding() {
        var res1 = String.format("%g", 0.00009999999999999995);
        var res2 = String.format("%g", 0.00009999999f);
        var res3 = String.format("%g", new BigDecimal(0.0001));
        var res4 = String.format("%g", new BigDecimal("0.00009999999999999999995"));

        assertEquals(res1, res2);
        assertEquals(res2, res3);
        assertEquals(res3, res4);

        var res5 = String.format("%.9g", 999999.999999432168754e+3);
        var res6 = String.format("%.9g", 999999999.999432168754f);
        var res7 = String.format("%.9g", new BigDecimal("999999.999999432168754e+3")); // !!
        var res8 = String.format("%.9g", new BigDecimal("1000000000")); // !!

        assertEquals(res5, res6);
        assertEquals(res6, res7);
        assertEquals(res7, res8);

    }
}