Information about constructors is elaborated. (#29852)

Information about empty constructors and parametrized constructors in Java is elaborated & default behavior of java is described.

guide/english/java/constructors/index.md

@@ -1,7 +1,7 @@
 ---
 title: Constructors
-
 ---
+
 Constructors are functions or methods in a program that creates an object of a class and can also initialize attributes for the object. The object is an instance of the class and can perform the methods/functions defined within the class.
 
 This includes **getter** (e.g., getName()) / **setter** (e.g., setName()) methods. Basically, every Java Class has a constructor which is the method called first when any object of the class is initialized. Think of it as the creation of a new attribute, not unlike the declaration of a new data type.
@@ -178,13 +178,12 @@ class Complex {
 }
 ```
 
-[run the full code](https://repl.it/MwnJ)
+- [run the full code](https://repl.it/MwnJ)
 
 ## Constructor Chaining
-
 A chaining constructor is when a constructor calls another constructor from the same class.It can be used for multiple ways to create one Object which can be useful.
 
-```Java
+```java
 class Number {
  
     int number;
@@ -209,5 +208,59 @@ class Number {
 }
 ```
 
-#### More Information:
+### Important things to note about Constructors in Java
+- It is not always necessary to have a constructor in Java. Java automatically make an empty constructor for you, BUT it is the case when you do not have a parameterized constructor.
+- If you have a parameterized constructor and you want to make an object with empty constructor (without any parameters) then it is not possible without creating an empty constructor yourself. <br /><br /> Lets look at this with an example:
+
+```java
+public class Test
+{
+
+}
+
+public static void main(String[] args) 
+{
+    Test b = new Test();    // It's ok, because we do not have a parametrized constructor
+}
+```
+
+But if there is a parametrized constructor and we wanted to make an object of that class without parametrized constructor, program will 
+not compile
+
+```java
+public class Test
+{
+    Test(int a)     // Parametrized Constructor
+    {
+    }
+}
+
+public static void main(String[] args) 
+{
+    // There will be an error on line below because we have a parametrized constructor and have not made an empty constructor ourselves 
+    Test b = new Test();   
+}
+```
+
+The above code should be changed to the following to compile properly:
+```java
+public class Test
+{
+    Test()      // Empty Constructor
+    {
+    } 
+    
+    Test(int a)     // Parametrized Constructor
+    {
+    }
+}
+
+public static void main(String[] args) 
+{
+    // Now this will compile properly 
+    Test b = new Test();   
+}
+```
+
+## Additional Resources
 - [Oracle Java Docs :Constructor Declarations](https://docs.oracle.com/javase/specs/jls/se7/html/jls-8.html#jls-8.8)