BAEL-5621 - parseInt vs valueOf in Java (#12275)

* Initial commit for Object copy in Java

* review comments commit for Object copy in Java

* Initial commit for parseInt vs valueOf java

* Review comments commit for parseInt vs valueOf java

* Modify readme

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* build failure retry remove parseInt(java.lang.String,int,int,int)

* build failure add comment

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core-java-modules/core-java-string-conversions-2/src/test/java/com/baeldung/stringtointeger/StringToIntegerUnitTest.java

@@ -0,0 +1,73 @@
+package com.baeldung.stringtointeger;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class StringToIntegerUnitTest {
+
+    @Test
+    public void whenValidNumericStringIsPassed_thenShouldConvertToPrimitiveInt() {
+        assertEquals(11, Integer.parseInt("11")); 
+        assertEquals(11, Integer.parseInt("+11")); 
+        assertEquals(-11, Integer.parseInt("-11"));
+    }
+
+    @Test
+    public void whenValidNumericStringWithRadixIsPassed_thenShouldConvertToPrimitiveInt() {
+        assertEquals(17, Integer.parseInt("11", 16)); 
+        assertEquals(10, Integer.parseInt("A", 16)); 
+        assertEquals(7, Integer.parseInt("7", 8));
+    }
+
+//    public static int parseInt(CharSequence s, int beginIndex, int endIndex, int radix) throws NumberFormatException 
+//    This method is available in JDK 9 and above  
+//    @Test
+//    public void whenValidNumericStringWithRadixAndSubstringIsPassed_thenShouldConvertToPrimitiveInt() {
+//        assertEquals(5, Integer.parseInt("100101", 3, 6, 2));
+//        assertEquals(101, Integer.parseInt("100101", 3, 6, 10));
+//    }
+
+    @Test(expected = NumberFormatException.class)
+    public void whenInValidNumericStringIsPassed_thenShouldThrowNumberFormatException() {
+        int number = Integer.parseInt("abcd");
+    }
+
+    @Test
+    public void whenValidNumericStringIsPassed_thenShouldConvertToInteger() {
+        Integer expectedNumber = 11;
+        Integer expectedNegativeNumber = -11;
+        
+        assertEquals(expectedNumber, Integer.valueOf("11"));
+        assertEquals(expectedNumber, Integer.valueOf("+11"));
+        assertEquals(expectedNegativeNumber, Integer.valueOf("-11"));
+    }
+
+    @Test
+    public void whenNumberIsPassed_thenShouldConvertToInteger() {
+        Integer expectedNumber = 11;
+        Integer expectedNegativeNumber = -11;
+        Integer expectedUnicodeValue = 65;
+        
+        assertEquals(expectedNumber, Integer.valueOf(11));
+        assertEquals(expectedNumber, Integer.valueOf(+11));
+        assertEquals(expectedNegativeNumber, Integer.valueOf(-11));
+        assertEquals(expectedUnicodeValue, Integer.valueOf('A'));
+    }
+
+    @Test
+    public void whenValidNumericStringWithRadixIsPassed_thenShouldConvertToInetger() {
+        Integer expectedNumber1 = 17;
+        Integer expectedNumber2 = 10;
+        Integer expectedNumber3 = 7;
+        
+        assertEquals(expectedNumber1, Integer.valueOf("11", 16));
+        assertEquals(expectedNumber2, Integer.valueOf("A", 16));
+        assertEquals(expectedNumber3, Integer.valueOf("7", 8));
+    }
+
+    @Test(expected = NumberFormatException.class)
+    public void whenInvalidValueOfNumericStringPassed_thenShouldThrowException() {
+        Integer number = Integer.valueOf("abcd");
+    }
+}