Enums in Java (#30882)

* Enums

Defining , accessing and comparison of enums to strings.

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guide/english/java/enums/index.md

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+---
+title: Enums in Java
+---
+
+Enum is a datatype introduced in Java to represent a list of predefined constants. 
+Enum can be defined independently outside a class or even inside a class.
+
+Consider the following example to define Enums independently:
+
+``` java
+public enum Status {
+  success, failure, pending;
+}
+```
+Consider the following example to define Enums inside a class:
+
+``` java
+public class EnumExample {
+  enum Status {
+    success, failure, pending;
+  }
+}
+```
+## Acessing Enum Values
+
+The value of Enums can be accessed directly, similar to a `static` variable.
+
+Consider the example when Enum is defined independently:
+
+``` java
+// This assigns the variable status with enum value pending.
+Status status = Status.pending;
+```
+Consider the example when Enum is defined inside a class:
+
+``` java
+// This assigns the variable status with enum value pending.
+Status status = EnumExample.Status.pending;
+```
+## Comparing value of a String to Enum constant
+
+Enums provide an imlpicit method `valueOf()` which takes a `String` as an input parameter and returns the enum constant of the specified string. The name of the input string must exactly match an identifier specified in the Enum list. If not, it throws an `IllegalArgumentException`.
+
+Consider the following example for comparing value of a string to an enum:
+
+``` java
+String input = "cancelled";
+System.out.println(Status.valueOf(input)); // cancelled
+```
+``` java
+String input = "can";
+System.out.println(Status.valueOf(input)); 
+
+// output : Exception in thread "main" java.lang.IllegalArgumentException: No enum constant Status.can
+```