BAEL-3141: Created new module for 'Converting Java String to Double' and other newly created string articles. (#7548)

java-strings-3/src/main/java/com/baeldung/string/README.md

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+This file exists to ensure this empty directory is committed in Git.
+
+Please remove this file when this directory is populated.

java-strings-3/src/main/resources/.gitignore

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+*.class
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+
+# Packaged files #
+*.jar
+*.war
+*.ear

java-strings-3/src/test/java/com/baeldung/string/todouble/StringToDoubleConversionUnitTest.java

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+package com.baeldung.string.todouble;
+
+import static org.junit.Assert.assertEquals;
+
+import java.text.DecimalFormat;
+import java.text.ParseException;
+
+import org.junit.Test;
+
+public class StringToDoubleConversionUnitTest {
+
+    @Test
+    public void givenValidString_WhenParseDouble_ThenResultIsPrimitiveDouble() {
+        assertEquals(1.23, Double.parseDouble("1.23"), 0.000001);
+    }
+    
+    @Test(expected = NullPointerException.class)
+    public void givenNullString_WhenParseDouble_ThenNullPointerExceptionIsThrown() {
+        Double.parseDouble(null);
+    }
+    
+    @Test(expected = NumberFormatException.class)
+    public void givenInalidString_WhenParseDouble_ThenNumberFormatExceptionIsThrown() {
+        Double.parseDouble("&");
+    }
+    
+    @Test
+    public void givenValidString_WhenValueOf_ThenResultIsPrimitiveDouble() {
+        assertEquals(1.23, Double.valueOf("1.23"), 0.000001);
+    }
+    
+    @Test(expected = NullPointerException.class)
+    public void givenNullString_WhenValueOf_ThenNullPointerExceptionIsThrown() {
+        Double.valueOf(null);
+    }
+    
+    @Test(expected = NumberFormatException.class)
+    public void givenInalidString_WhenValueOf_ThenNumberFormatExceptionIsThrown() {
+        Double.valueOf("&");
+    }
+    
+    @Test
+    public void givenValidString_WhenDecimalFormat_ThenResultIsValidDouble() throws ParseException {
+        assertEquals(1.23, new DecimalFormat("#").parse("1.23").doubleValue(), 0.000001);
+    }
+    
+    @Test(expected = NullPointerException.class)
+    public void givenNullString_WhenDecimalFormat_ThenNullPointerExceptionIsThrown() throws ParseException {
+        new DecimalFormat("#").parse(null);
+    }
+    
+    @Test(expected = ParseException.class)
+    public void givenInvalidString_WhenDecimalFormat_ThenParseExceptionIsThrown() throws ParseException {
+        new DecimalFormat("#").parse("&");
+    }
+}

java-strings-3/src/test/resources/.gitignore

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+*.class
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+
+# Packaged files #
+*.jar
+*.war
+*.ear