Java 创建常量有几种方式？

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1. 问题

• 创建常量有几种方式？

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2. 解答

• Java 中创建常量有 3 种方式，分别可以通过 Enum 来创建，在普通类中通过 static final 修饰变量，或者通过 Interface 来创建变量。

a. Enum 中创建常量

enum ConstantEnum {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY
}

b. 在普通类中使用 static final 修饰变量

public class ConstantClassField {
    public static final String SUNDAY = "SUNDAY";
    public static final String MONDAY = "MONDAY";
    public static final String TUESDAY = "TUESDAY";
    public static final String WEDNESDAY = "WEDNESDAY";
    public static final String THURSDAY = "THURSDAY";
    public static final String FRIDAY = "FRIDAY";
    public static final String SATURDAY = "SATURDAY";
}

c. 在 Interface 中创建常量

• 接口（Interface）中的变量默认为 static final 的特性。

public interface ConstantInterface {  
    String SUNDAY = "SUNDAY";  
    String MONDAY = "MONDAY";  
    String TUESDAY = "TUESDAY";  
    String WEDNESDAY = "WEDNESDAY";  
    String THURSDAY = "THURSDAY";  
    String FRIDAY = "FRIDAY";  
    String SATURDAY = "SATURDAY";  
}