Merge pull request #9344 from marcinkrykowski/number-formatting-java

Add Format Number implementation and tests

java-numbers-3/src/main/java/com/baeldung/formatNumber/FormatNumber.java

@@ -0,0 +1,73 @@
+package com.baeldung.formatNumber;
+
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+import java.text.DecimalFormat;
+import java.text.NumberFormat;
+import java.util.Locale;
+
+public class FormatNumber {
+    public static double withBigDecimal(double value, int places) {
+        if (places < 0)
+            throw new IllegalArgumentException();
+
+        BigDecimal bigDecimal = new BigDecimal(value);
+        bigDecimal = bigDecimal.setScale(places, RoundingMode.HALF_UP);
+        return bigDecimal.doubleValue();
+    }
+
+    public static double withMathRound(double value, int places) {
+        double scale = Math.pow(10, places);
+        return Math.round(value * scale) / scale;
+    }
+
+    public static double withDecimalFormatPattern(double value, int places) {
+        DecimalFormat df2 = new DecimalFormat("#,###,###,##0.00");
+        DecimalFormat df3 = new DecimalFormat("#,###,###,##0.000");
+        if (places == 2)
+            return new Double(df2.format(value));
+        else if (places == 3)
+            return new Double(df3.format(value));
+        else
+            throw new IllegalArgumentException();
+    }
+
+    public static double withDecimalFormatLocal(double value) {
+        DecimalFormat df = (DecimalFormat) NumberFormat.getNumberInstance(Locale.getDefault());
+        return new Double(df.format(value));
+    }
+
+    public static String withStringFormat(double value, int places) {
+        return String.format("%." + places + "f", value);
+    }
+
+    public static String byPaddingZeros(int value, int paddingLength) {
+        return String.format("%0" + paddingLength + "d", value);
+    }
+
+    public static double withTwoDecimalPlaces(double value) {
+        DecimalFormat df = new DecimalFormat("#.00");
+        return new Double(df.format(value));
+    }
+
+    public static String withLargeIntegers(double value) {
+        DecimalFormat df = new DecimalFormat("###,###,###");
+        return df.format(value);
+    }
+
+    public static String forPercentages(double value, Locale localisation) {
+        NumberFormat nf = NumberFormat.getPercentInstance(localisation);
+        return nf.format(value);
+    }
+
+    public static String currencyWithChosenLocalisation(double value, Locale localisation) {
+        NumberFormat nf = NumberFormat.getCurrencyInstance(localisation);
+        return nf.format(value);
+    }
+
+    public static String currencyWithDefaultLocalisation(double value) {
+        NumberFormat nf = NumberFormat.getCurrencyInstance();
+        return nf.format(value);
+    }
+}
+

java-numbers-3/src/test/java/com/baeldung/formatNumber/FormatNumberUnitTest.java

@@ -0,0 +1,82 @@
+package com.baeldung.formatNumber;
+
+import org.junit.Test;
+
+import java.util.Locale;
+
+import static com.baeldung.formatNumber.FormatNumber.*;
+import static org.assertj.core.api.Assertions.*;
+
+public class FormatNumberUnitTest {
+    private static final double D = 4.2352989244d;
+    private static final double F = 8.6994540927d;
+
+    @Test
+    public void givenDecimalNumber_whenFormatNumberWithBigDecimal_thenGetExpectedResult() {
+        assertThat(withBigDecimal(D, 2)).isEqualTo(4.24);
+        assertThat(withBigDecimal(D, 3)).isEqualTo(4.235);
+        assertThat(withBigDecimal(F, 2)).isEqualTo(8.7);
+        assertThat(withBigDecimal(F, 3)).isEqualTo(8.699);
+    }
+
+    @Test
+    public void givenDecimalNumber_whenFormatNumberWithDecimalFormat_thenGetExpectedResult() {
+        assertThat(withDecimalFormatLocal(D)).isEqualTo(4.235);
+        assertThat(withDecimalFormatLocal(F)).isEqualTo(8.699);
+
+        assertThat(withDecimalFormatPattern(D, 2)).isEqualTo(4.24);
+        assertThat(withDecimalFormatPattern(D, 3)).isEqualTo(4.235);
+        assertThat(withDecimalFormatPattern(F, 2)).isEqualTo(8.7);
+        assertThat(withDecimalFormatPattern(F, 3)).isEqualTo(8.699);
+    }
+
+    @Test
+    public void givenDecimalNumber_whenFormatNumberWithStringFormat_thenGetExpectedResult() {
+        assertThat(withStringFormat(D, 2)).isEqualTo("4.24");
+        assertThat(withStringFormat(D, 3)).isEqualTo("4.235");
+        assertThat(withStringFormat(F, 2)).isEqualTo("8.70");
+        assertThat(withStringFormat(F, 3)).isEqualTo("8.699");
+    }
+
+    @Test
+    public void givenDecimalNumber_whenFormatNumberWithMathRound_thenGetExpectedResult() {
+        assertThat(withMathRound(D, 2)).isEqualTo(4.24);
+        assertThat(withMathRound(D, 3)).isEqualTo(4.235);
+        assertThat(withMathRound(F, 2)).isEqualTo(8.7);
+        assertThat(withMathRound(F, 3)).isEqualTo(8.699);
+    }
+
+    @Test
+    public void givenIntegerNumber_whenFormatNumberByPaddingOutZeros_thenGetExpectedResult() {
+        int value = 1;
+        assertThat(byPaddingZeros(value, 3)).isEqualTo("001");
+    }
+
+    @Test
+    public void givenIntegerNumber_whenFormatNumberWithTwoDecimalPlaces_thenGetExpectedResult() {
+        int value = 12;
+        assertThat(withTwoDecimalPlaces(value)).isEqualTo(12.00);
+    }
+
+    @Test
+    public void givenIntegerNumber_whenFormatNumberWithLargeIntegers_thenGetExpectedResult() {
+        int value = 123456789;
+        assertThat(withLargeIntegers(value)).isEqualTo("123,456,789");
+    }
+
+    @Test
+    public void givenDecimalNumber_whenFormatNumberForPercentages_thenGetExpectedResult() {
+        double value = 25f / 100f;
+        assertThat(forPercentages(value, new Locale("en", "US"))).isEqualTo("25%");
+        assertThat(forPercentages(value, new Locale("pl", "PL"))).isEqualTo("25%");
+    }
+
+    @Test
+    public void givenCurrency_whenFormatNumberCurrencyWithChosenLocalisation_thenGetExpectedResult() {
+        double value = 23_500;
+        assertThat(currencyWithChosenLocalisation(value, new Locale("en", "US"))).isEqualTo("$23,500.00");
+        assertThat(currencyWithChosenLocalisation(value, new Locale("zh", "CN"))).isEqualTo("￥23,500.00");
+        assertThat(currencyWithChosenLocalisation(value, new Locale("pl", "PL"))).isEqualTo("23 500 zł");
+    }
+
+}