Java中的枚舉（enum）是一種特殊的類，用于表示固定數(shù)量的常量值。1. 使用enum關(guān)鍵字定義；2. 每個枚舉值都是該枚舉類型的公共靜態(tài)最終實例；3. 可以包含字段、構(gòu)造函數(shù)和方法，為每個常量添加行為；4. 可在switch語句中使用，支持直接比較，并提供name()、ordinal()、values()和valueOf()等內(nèi)置方法；5. 枚舉可提升代碼的類型安全性、可讀性和靈活性，適用于狀態(tài)碼、顏色或星期等有限集合場景。
Enums in Java are a special type of class that represent a fixed number of constant values. They're commonly used when you have a variable that should only hold one of a small set of possible values—like days of the week, colors, or status codes.
How to Define an Enum
You define an enum using the enum keyword. Here's a basic example:
public enum Day {
MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
}Each value (like MONDAY, TUESDAY, etc.) is an instance of the Day enum. Behind the scenes, Java creates a class that extends java.lang.Enum, so enums come with some built-in methods.
Some key points:
- Enums can be declared outside or inside a class, but not inside a method.
- Each enum constant is implicitly
public static final.
Common Uses of Enums
Enums are more than just named constants. You can add fields, constructors, and methods to them.
For example, let’s say you want each day to have a "type":
public enum Day {
MONDAY("Weekday"),
TUESDAY("Weekday"),
WEDNESDAY("Weekday"),
THURSDAY("Weekday"),
FRIDAY("Weekday"),
SATURDAY("Weekend"),
SUNDAY("Weekend");
private String type;
Day(String type) {
this.type = type;
}
public String getType() {
return type;
}
}Now, each day has additional behavior. This makes enums very useful for grouping related constants with shared logic.
Working with Enums in Code
You can use enums in switch statements, compare them directly, and get their names or ordinal positions.
Here’s how you might use it:
Day today = Day.MONDAY;
System.out.println(today); // Output: MONDAY
System.out.println(today.getType()); // Output: Weekday
if (today.getType().equals("Weekend")) {
System.out.println("Time to relax!");
} else {
System.out.println("Time to work.");
}Useful methods you'll often see:
-
name()– returns the name of the enum constant. -
ordinal()– returns the position in the enum declaration (starts at 0). -
values()– returns an array of all enum constants. -
valueOf(String)– returns the enum constant matching the given name.
Enums give you a clean way to model fixed sets of related data. They’re type-safe, readable, and flexible enough to handle many real-world scenarios without needing extra classes or constants.基本上就這些。
The above is the detailed content of What is the `enum` type in Java?. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
Selecting Specific Columns | Performance Optimization
Jun 27, 2025 pm 05:46 PM
Selectingonlyneededcolumnsimprovesperformancebyreducingresourceusage.1.Fetchingallcolumnsincreasesmemory,network,andprocessingoverhead.2.Unnecessarydataretrievalpreventseffectiveindexuse,raisesdiskI/O,andslowsqueryexecution.3.Tooptimize,identifyrequi
What is the `enum` type in Java?
Jul 02, 2025 am 01:31 AM
Enums in Java are special classes that represent fixed number of constant values. 1. Use the enum keyword definition; 2. Each enum value is a public static final instance of the enum type; 3. It can include fields, constructors and methods to add behavior to each constant; 4. It can be used in switch statements, supports direct comparison, and provides built-in methods such as name(), ordinal(), values() and valueOf(); 5. Enumeration can improve the type safety, readability and flexibility of the code, and is suitable for limited collection scenarios such as status codes, colors or week.
What is the JDK?
Jun 25, 2025 pm 04:05 PM
JDK (JavaDevelopmentKit) is a software development environment for developing Java applications and applets. It contains tools and libraries required to compile, debug and run Java programs. Its core components include Java compiler (javac), Java runtime environment (JRE), Java interpreter (java), debugger (jdb), document generation tools (javadoc) and packaging tools (such as jar and jmod). Developers need JDK to write, compile Java code and develop with the help of IDE; without JDK, Java applications cannot be built or modified. You can enter javac-version and java-version in the terminal
Applying Semantic Structure with article, section, and aside in HTML
Jul 05, 2025 am 02:03 AM
The rational use of semantic tags in HTML can improve page structure clarity, accessibility and SEO effects. 1. Used for independent content blocks, such as blog posts or comments, it must be self-contained; 2. Used for classification related content, usually including titles, and is suitable for different modules of the page; 3. Used for auxiliary information related to the main content but not core, such as sidebar recommendations or author profiles. In actual development, labels should be combined and other, avoid excessive nesting, keep the structure simple, and verify the rationality of the structure through developer tools.
VSCode debugger for Java setup guide
Jul 01, 2025 am 12:22 AM
The key steps in configuring the Java debugging environment on VSCode include: 1. Install JDK and verify; 2. Install JavaExtensionPack and DebuggerforJava plug-in; 3. Create and configure the launch.json file, specify mainClass and projectName; 4. Set up the correct project structure to ensure the source code path and compilation output are correct; 5. Use debugging techniques such as Watch, F8/F10/F11 shortcut keys and methods to deal with common problems such as class not found or JVM attachment failure.
XML rules: Common errors to avoid
Jun 22, 2025 am 12:09 AM
Methods to avoid XML errors include: 1. Ensure that the elements are nested correctly, 2. Escape special characters. Correct nesting avoids parsing errors, while escape characters prevent document corruption, using an XML editor can help maintain structural integrity.
How do I set up VS Code for Java development?
Jun 29, 2025 am 12:23 AM
To use VSCode for Java development, you need to install the necessary extensions, configure the JDK and set up the workspace. 1. Install JavaExtensionPack, including language support, debugging integration, build tools and code completion functions; optional JavaTestRunner or SpringBoot extension package. 2. Install at least JDK17 and verify through java-version and javac-version; set the JAVA_HOME environment variable, or switch multiple JDKs in the status bar at the bottom of VSCode. 3. After opening the project folder, make sure the project structure is correct and enable automatic saving, adjust the formatting rules, enable code checking, and configure the compilation task to optimize the opening.
Windows search bar not typing
Jul 02, 2025 am 10:55 AM
When the Windows search bar cannot enter text, common solutions are: 1. Restart the Explorer or computer, open the Task Manager to restart the "Windows Explorer" process, or restart the device directly; 2. Switch or uninstall the input method, try to use the English input method or Microsoft's own input method to eliminate third-party input method conflicts; 3. Run the system file check tool, execute the sfc/scannow command in the command prompt to repair the system files; 4. Reset or rebuild the search index, and rebuild it through the "Index Options" in the "Control Panel". Usually, we start with simple steps first, and most problems can be solved step by step.
