Summarize of seven common usages of Java enumeration (must read)

Usage 1: Constant

Before JDK1.5, we defined constants: publicstaticfianl.... Now that with the enum, you can group the relevant constants into an enum type, and enums provide more methods than constants.

Java code

 public enum Color {RED, GREEN, BLANK, YELLOW}

Usage 2: switch

The switch statements before JDK1.6 only support int, char, and enum types. The use of enums can make our code more readable.

Java code

 enum Signal {GREEN, YELLOW, RED}public class TrafficLight {Signal color = Signal.RED;public void change() {switch (color) {case RED:color = Signal.GREEN;break;case YELLOW:color = Signal.RED;break;case GREEN:color = Signal.YELLOW;break;}}}

Usage 3: Add a new method to the enum

If you plan to customize your own method, you must add a semicolon at the end of the enum instance sequence. And Java requires that the enum instance must be defined first.

Java code

 public enum Color {RED("red", 1), GREEN("green", 2), BLANK("white", 3), YELLO("yellow", 4);// Member variable private String name;private int index;// Construct method private Color(String name, int index) {this.name = name;this.index = index;}// Normal method public static String getName(int index) {for (Color c : Color.values()) {if (c.getIndex() == index) {return c.name;}}return null;}// get set method public String getName() {return name;}public void setName(String name) {this.name = name;}public int getIndex() {return index;}public void setIndex(int ​​index) {this.index = index;}}

Usage 4: Methods to overwrite enumeration

Here is an example of the toString() method override.

Java code

 public enum Color {RED("red", 1), GREEN("green", 2), BLANK("white", 3), YELLO("yellow", 4);// Member variable private String name;private int index;// Construct method private Color(String name, int index) {this.name = name;this.index = index;}// Overwrite method @Overridepublic String toString() {return this.index+"_"+this.name;}}

Usage 5: Implement the interface

All enums are inherited from the java.lang.Enum class. Since Java does not support multiple inheritance, enum objects cannot inherit other classes.

Java code

 public interface Behaviour {void print();String getInfo();}public enum Color implements Behaviour{RED("red", 1), GREEN("green", 2), BLANK("white", 3), YELLO("yellow", 4);// Member variable private String name;private int index;// Construct method private Color(String name, int index) {this.name = name;this.index = index;}// Interface method @Overridepublic String getInfo() {return this.name;}//Interface method @Overridepublic void print() {System.out.println(this.index+":"+this.name);}}

Usage 6: Use interface to organize enumeration

Java code

 public interface Food {enum Coffee implements Food{BLACK_COFFEE,DECAF_COFFEE,LATTE,CAPPUCCINO}enum Dessert implements Food{FRUIT, CAKE, GELATO}}

Usage 7: About the use of enumeration collections

java.util.EnumSet and java.util.EnumMap are two enum collections. EnumSet ensures that elements in the collection are not repeated; the key in EnumMap is of type enum, and value can be of any type. I will not elaborate on the use of these two sets here, please refer to the JDK documentation.

The above is the summary of seven common usages of Java enumerations (must read) brought to you by the editor. I hope you will support Wulin.com more~