How to get java enum value

How to get java enum value

This is the common base class of all Java language enumeration types. More information about enums, including descriptions of the implicitly declared methods synthesized by the compiler, can be found in section 8.9 of The Java™ Language Specification . Note that when using an enumeration type as the type of a set or as the type of the keys in a map, specialized and efficient set and map implementations are available.

Constructor Summary

Method Summary

Returns the ordinal of this enumeration constant (its position in its enum declaration, where the initial constant is assigned an ordinal of zero).

Methods inherited from class java.lang.Object

Constructor Detail

Enum

Sole constructor. Programmers cannot invoke this constructor. It is for use by code emitted by the compiler in response to enum type declarations.

Method Detail

name

Returns the name of this enum constant, exactly as declared in its enum declaration. Most programmers should use the toString() method in preference to this one, as the toString method may return a more user-friendly name. This method is designed primarily for use in specialized situations where correctness depends on getting the exact name, which will not vary from release to release.

ordinal

Returns the ordinal of this enumeration constant (its position in its enum declaration, where the initial constant is assigned an ordinal of zero). Most programmers will have no use for this method. It is designed for use by sophisticated enum-based data structures, such as EnumSet and EnumMap .

toString

Returns the name of this enum constant, as contained in the declaration. This method may be overridden, though it typically isn’t necessary or desirable. An enum type should override this method when a more «programmer-friendly» string form exists.

equals

hashCode

public final int hashCode()

clone

protected final Object clone() throws CloneNotSupportedException

Throws CloneNotSupportedException. This guarantees that enums are never cloned, which is necessary to preserve their «singleton» status.

compareTo

Compares this enum with the specified object for order. Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object. Enum constants are only comparable to other enum constants of the same enum type. The natural order implemented by this method is the order in which the constants are declared.

getDeclaringClass

Returns the Class object corresponding to this enum constant’s enum type. Two enum constants e1 and e2 are of the same enum type if and only if e1.getDeclaringClass() == e2.getDeclaringClass(). (The value returned by this method may differ from the one returned by the Object.getClass() method for enum constants with constant-specific class bodies.)

valueOf

public static Enum> T valueOf(Class enumType, String name)

Returns the enum constant of the specified enum type with the specified name. The name must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.) Note that for a particular enum type T , the implicitly declared public static T valueOf(String) method on that enum may be used instead of this method to map from a name to the corresponding enum constant. All the constants of an enum type can be obtained by calling the implicit public static T[] values() method of that type.

finalize

protected final void finalize()

Источник

How to get an enum value from a String in Java?

An enum is a special class in Java that represents a group of constants. In this short tutorial, we are going to present how to get enum value using String.

2. The problem: Get enum using String value

Let’s say we have the following enum Alphabet :

We want to find the enum value of a String, for example, «A» which would be Alphabet.A .

3. Solution1: Use Enum.valueOf(. ) method

Use Alphabet.valueOf(str) method.

This method returns the enum with the specified name. The name must match exactly an identifier. For example to get Alphabet.A we need to use Alphabet.valueOf(«A») .

Note that if the specified enum type has no constant with the specified name the IllegalArgumentException will the thrown.

• Alphabet.valueOf(«A «) — note space at the end,
• Alphabet.valueOf(«9») — no such contant in Alphaget enum,
• Alphabet.valueOf(«a») — method is case sensitive.

4. Solution2: Filtering enum values

You can also manually filter enum values from specified type like in the following example:

import java.util.Arrays; public enum Alphabet < A, B, C, D, E, F, G; public static Alphabet findCaseInsensitive(String str) < return Arrays.stream(Alphabet.values()) .filter(alphabet ->str.equalsIgnoreCase(alphabet.name())) .findFirst() .orElseThrow(() -> new IllegalArgumentException("No constant found")); > > 

In this example we used String.equalsIgnoreCase(. ) to compare specified String with enum values in case-insensitive way.

Now to find Alphabet.A we can use this method like in the following snippet:

Alphabet al = Alphabet.findCaseInsensitive("a"); 

The al variable will be equal to Alphabet.A

5. Solution3: Checking enum values without throwing an exception

To check if enum contains constant A without throwing an exception we can use Guava library.

In the following code we used Enums utility class from Guava :

Optional opt = Enums.getIfPresent(Alphabet.class, "A") 

The getIfPresent(. ) method will return Optional.empty() if Alphabet doesn’t have A value.

You can also implement this method on your own in Plain Java:

import java.util.Arrays; public enum Alphabet < A, B, C, D, E, F, G; public static OptionalgetIfPresent(String str) < return Arrays.stream(Alphabet.values()) .filter(alphabet ->str.equals(alphabet.name())) .findFirst(); > > 

Источник

How to get java enum value

• Introduction to Java
• The complete History of Java Programming Language
• C++ vs Java vs Python
• How to Download and Install Java for 64 bit machine?
• Setting up the environment in Java
• How to Download and Install Eclipse on Windows?
• JDK in Java
• How JVM Works – JVM Architecture?
• Differences between JDK, JRE and JVM
• Just In Time Compiler
• Difference between JIT and JVM in Java
• Difference between Byte Code and Machine Code
• How is Java platform independent?

• Decision Making in Java (if, if-else, switch, break, continue, jump)
• Java if statement with Examples
• Java if-else
• Java if-else-if ladder with Examples
• Loops in Java
• For Loop in Java
• Java while loop with Examples
• Java do-while loop with Examples
• For-each loop in Java
• Continue Statement in Java
• Break statement in Java
• Usage of Break keyword in Java
• return keyword in Java

• Object Oriented Programming (OOPs) Concept in Java
• Why Java is not a purely Object-Oriented Language?
• Classes and Objects in Java
• Naming Conventions in Java
• Java Methods
• Access Modifiers in Java
• Java Constructors
• Four Main Object Oriented Programming Concepts of Java
• Inheritance in Java
• Abstraction in Java
• Encapsulation in Java
• Polymorphism in Java
• Interfaces in Java
• ‘this’ reference in Java

Источник

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());

Источник