Merge pull request #14863 from sam-gardner/BAEL-6895-truncating-doubles-to-two-decimal-places

BAEL-6895 Add code for truncating a double to two decimal places

core-java-modules/core-java-numbers-6/src/test/java/com/baeldung/truncatedouble/TruncateDoubleUnitTest.java

@@ -0,0 +1,73 @@
+package com.baeldung.truncatedouble;
+
+import static org.junit.Assert.assertEquals;
+
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+import java.text.DecimalFormat;
+import java.text.NumberFormat;
+
+import org.junit.Test;
+
+public class TruncateDoubleUnitTest {
+
+    @Test
+    public void givenADouble_whenUsingDecimalFormat_truncateToTwoDecimalPlaces() {
+        DecimalFormat df = new DecimalFormat("#.##");
+        df.setRoundingMode(RoundingMode.DOWN);
+
+        double value = 1.55555555;
+        String truncated = df.format(value);
+        assertEquals("1.55", truncated);
+
+        double negativeValue = -1.55555555;
+        String negativeTruncated = df.format(negativeValue);
+        assertEquals("-1.55", negativeTruncated);
+    }
+
+    @Test
+    public void givenADouble_whenUsingNumberFormat_truncateToTwoDecimalPlaces() {
+        NumberFormat nf = NumberFormat.getNumberInstance();
+        nf.setMaximumFractionDigits(2);
+        nf.setRoundingMode(RoundingMode.DOWN);
+
+        double value = 1.55555555;
+        String truncated = nf.format(value);
+        assertEquals("1.55", truncated);
+
+        double negativeValue = -1.55555555;
+        String negativeTruncated = nf.format(negativeValue);
+        assertEquals("-1.55", negativeTruncated);
+    }
+
+    @Test
+    public void givenADouble_whenUsingBigDecimal_truncateToTwoDecimalPlaces() {
+        BigDecimal positive = new BigDecimal(2.555555).setScale(2, RoundingMode.DOWN);
+        BigDecimal negative = new BigDecimal(-2.555555).setScale(2, RoundingMode.DOWN);
+        assertEquals("2.55", positive.toString());
+        assertEquals("-2.55", negative.toString());
+    }
+
+    @Test
+    public void givenADouble_whenUsingMath_truncateToTwoDecimalPlaces() {
+        double positive = 1.55555555;
+        double truncated = Math.floor(positive * 100) / 100;
+        assertEquals("1.55", String.valueOf(truncated));
+
+        double negative = -1.55555555;
+        double negativeTruncated = Math.ceil(negative * 100) / 100;
+        assertEquals("-1.55", String.valueOf(negativeTruncated));
+    }
+
+    @Test
+    public void givenADouble_whenUsingStringFormat_truncateToTwoDecimalPlaces() {
+        double positive = 1.55555555;
+        String truncated = String.format("%.2f", positive);
+        assertEquals("1.56", truncated);
+
+        double negative = -1.55555555;
+        String negativeTruncated = String.format("%.2f", negative);
+        assertEquals("-1.56", negativeTruncated);
+    }
+
+}