What is enumeration string in java

enum in java

The enum in java is a special type of data types like Class and Interface. A Java enum is used to define collections of constants. It is also known as enumeration java. By the use of an enum, we can define a group of constants with all possible values at compile time. We can change the number of constants later and it doesn’t fit all time. Enum was introduced in JDK 1.5.

For example, we can use of enum in java to store the days of the week (SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, and SATURDAY). Because we know all the possible values at compile time. As per the naming conventions of the enum, all constants should be in capital letters.

Important points about enum

1. It is special data that is used to define a set of constants and the value of the constant defined at compile time.

2. All the constants of the enum are by default static and final. So, we can’t change the value of the constant. As constants are static so they are accessible by enum name.

3. A enum can have methods, constructors, and fields.

4. Java enums extend the Enum class that exists in java.lang package. The Enum class is an abstract class that implements a Comparable interface and serialize interface.

5. A enum can implements interfaces but can’t extend the class because it already internally extending the Enum class.

6. A enum can have numeric or string data constants.

How to create an enum

To create an enum we have to use an enum keyword like class keyword. It is the way to in java define enum.

accessModifier, we can provide access modifiers according to to use like default, and public.
enum, it is a predefined keyword.
enumName, which is the name of the enum to declare.
constant, We can have any number of constants.
methods, We can have any number of methods.

Java enum example

Here you can see the enum keyword that is used in place of class or interface . The enum keyword indicates to the compiler that this type of definition is an enum.

How to use of enum

Suppose we have an enum Week that contains some constants. You can access any constant by using the enum name because all constants are static. Here is the syntax to access the constant.

You can refer to the constants in the enum above like this:

Week constantFromEnum = Week.MONDAY;

enum Week < SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY; >public class EnumExample < public static void main(String arg[]) < // Getting a constant Week constantFromEnum = Week.MONDAY; System.out.println(constantFromEnum); >>

How to create Java enum methods and java enum constructor

We can create methods and constructors in an enum and use those methods to operate the constants of Enum.

Let’s see an example with a constructor and method. Here we are creating constants with an int code. So, we must provide a constructor that can take a parameter of int type otherwise compiler shows an error. This constructor internally involving by the compiler to set the code in constructors. Here we are creating a method that will return the code of each constant.

enum Week < SUNDAY(1), MONDAY(2), TUESDAY(3), WEDNESDAY(4), THURSDAY(5), FRIDAY(6), SATURDAY(7); private final int code; // Compiler internally invokes it to assign value Week(int code) < this.code = code; >public int getCode() < return code; >> public class EnumExample < public static void main(String arg[]) < // Getting a constant Week constantFromEnum = Week.MONDAY; System.out.println(constantFromEnum); System.out.println(constantFromEnum.getCode()); >>

How to use String in Java enum string value

We can use any type of value in enum constants. Let’s see the example with a string value.

enum Week < SUNDAY(1, "First day"), MONDAY(2, "Second day"), TUESDAY(3, "Third day"), WEDNESDAY(4, "Fourth day"), THURSDAY(5, "Fifth day"), FRIDAY(6, "Sixth day"), SATURDAY(7, "Seventh day"); private final int intCode; private final String stringCode; // Compiler internally invokes it to assign value Week(int intCode, String stringCode) < this.intCode = intCode; this.stringCode = stringCode; >public int getIntCode() < return intCode; >public String getStringCode() < return stringCode; >> public class EnumExample < public static void main(String arg[]) < // Getting a constant Week constantFromEnum = Week.MONDAY; System.out.println(constantFromEnum); System.out.println(constantFromEnum.getIntCode()); System.out.println(constantFromEnum.getStringCode()); >>

Methods of enum

Java enum class provides some predefined methods that are used to operate the values of an enum. Here we will discuss the most common method of the enum class.

compareTo() method

The compareTo() method is used to compare the constants of an enum. It compares the constant based on ordinal values.

enum Week < SUNDAY(1, "First day"), MONDAY(2, "Second day"), TUESDAY(3, "Third day"), WEDNESDAY(4, "Fourth day"), THURSDAY(5, "Fifth day"), FRIDAY(6, "Sixth day"), SATURDAY(7, "Seventh day"); private final int intCode; private final String stringCode; // Compiler internally invokes it to assign value Week(int intCode, String stringCode) < this.intCode = intCode; this.stringCode = stringCode; >public int getIntCode() < return intCode; >public String getStringCode() < return stringCode; >> public class EnumExample < public static void main(String arg[]) < System.out.println(Week.SUNDAY.compareTo(Week.MONDAY)); >>

toString() method

The toString() method converts the name of an enum to a string.

enum Week < SUNDAY(1, "First day"), MONDAY(2, "Second day"), TUESDAY(3, "Third day"), WEDNESDAY(4, "Fourth day"), THURSDAY(5, "Fifth day"), FRIDAY(6, "Sixth day"), SATURDAY(7, "Seventh day"); private final int intCode; private final String stringCode; // Compiler internally invokes it to assign value Week(int intCode, String stringCode) < this.intCode = intCode; this.stringCode = stringCode; >public int getIntCode() < return intCode; >public String getStringCode() < return stringCode; >> public class EnumExample < public static void main(String arg[]) < System.out.println(Week.SUNDAY.toString()); >>

Java enum valueof() method

The valueOf() method is a static method in the enum class and it is used to obtain an instance of the enum class for a given String value.

enum Week < SUNDAY(1, "First day"), MONDAY(2, "Second day"), TUESDAY(3, "Third day"), WEDNESDAY(4, "Fourth day"), THURSDAY(5, "Fifth day"), FRIDAY(6, "Sixth day"), SATURDAY(7, "Seventh day"); private final int intCode; private final String stringCode; // Compiler internally invokes it to assign value Week(int intCode, String stringCode) < this.intCode = intCode; this.stringCode = stringCode; >public int getIntCode() < return intCode; >public String getStringCode() < return stringCode; >> public class EnumExample < public static void main(String arg[]) < Week week = Week.valueOf("SUNDAY"); System.out.println(week); >>

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            Java Enum with Strings

            In this guide to Java enum with string values, learn to create enum using strings, iterate over all enum values, get enum value and perform a reverse lookup to find an enum by string parameter.

            We should always create enum when we have a fixed set of related constants. Enums are inherently singleton, so they provide better performance.

            1. Creating Enum with Strings

            Java program to create an enum with strings. The given enum contains deployment environments and their respective URLs. URLs are passed to the enum constructor for each enum constant.

            public enum Environment < PROD("https://prod.domain.com:1088/"), SIT("https://sit.domain.com:2019/"), CIT("https://cit.domain.com:8080/"), DEV("https://dev.domain.com:21323/"); private String url; Environment(String envUrl) < this.url = envUrl; >public String getUrl() < return url; >>

            2. Iterating over Enum Constants

            To iterate over enum list, use values() method on enum type which returns all enum constants in an array.

            //Get all enums for(Environment env : Environment.values())

            PROD :: https://prod.domain.com:1088/ SIT :: https://sit.domain.com:2019/ CIT :: https://cit.domain.com:8080/ DEV :: https://dev.domain.com:21323/

            To get a single enum value (e.g., get production URL from enum constant), use the getUrl() method that we created.

            String prodUrl = Environment.PROD.getUrl(); System.out.println(prodUrl);

            If we want to get enum constant using its name, then we should use valueOf() method.

            Environment sitUrl = Environment.valueOf("SIT"); System.out.println(sitUrl.getUrl());

            5. Reverse Lookup – Get Enum Name from Value

            We will often have the value of enum with us, and we will need to get the enum name by its value. This is achieved using a reverse lookup.

            enum Environment < PROD("https://prod.domain.com:1088/"), SIT("https://sit.domain.com:2019/"), CIT("https://cit.domain.com:8080/"), DEV("https://dev.domain.com:21323/"); private String url; Environment(String envUrl) < this.url = envUrl; >public String getUrl() < return url; >//****** Reverse Lookup ************// public static Optional get(String url) < return Arrays.stream(Environment.values()) .filter(env ->env.url.equals(url)) .findFirst(); > >

            To use the reverse lookup in the application code, use enum.get() method.

            String url = "https://sit.domain.com:2019/"; Optional env = Environment.get(url); System.out.println(env.get());

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