How to define class constants in Java?

1. In Java, we often hope that a certain constant can be used in multiple methods of a class. These constants are usually called class constants.

You can use the keyword static final to set a class constant.

2. The definition of a class constant is located outside the main method. Therefore, this constant can also be used in other methods of the same class.

Moreover, if a constant is declared as public, then methods of other classes can also use this constant.

Example

package cn.itcast.estore.util;
 
public final class Constant {
private Constant() {
super();
}
 
/******************************* Common常量列表 *********************************/
/**
 * Common常量列表(存放公共的常量)
 ***/
public static final class Common {
 
private static final int INT_ZERO = 0;
private static final int INT_ONE = 1;
private static final String IDENTIFYING_CODE = "identifying_code";
private static final String ENCODING_TYPE_UTF8 = "UTF-8";
private static final String ENCODING_TYPE_ISO8895_1 = "ISO-8859-1";
private static final String ENCODING_TYPE_GBK = "GBK";
private static final String CONTENT_TYPE_TextHtml = "text/html";
private static final String GET = "GET";
private static final String POST = "POST";
private static final String ENCRYPT_TYPE_MD5 = "md5";
private static final String ENCRYPT_TYPE_SHA1 = "sha1";
 
// 私有
private Common() {
super();
}
 
// 常量 "0"
public static int INT_ZERO() {
return INT_ZERO;
}
 
// 常量 "1"
public static int INT_ONE() {
return INT_ONE;
}
 
// 验证码常量名
public static String IDENTIFYING_CODE() {
return IDENTIFYING_CODE;
}
 
// utf8 编码类型
public static String ENCODING_TYPE_UTF8() {
return ENCODING_TYPE_UTF8;
}
// ISO-8859-1 编码类型
 
public static String ENCODING_TYPE_ISO8895_1() {
return ENCODING_TYPE_ISO8895_1;
}
 
// GBK 编码类型
 
public static String ENCODING_TYPE_GBK() {
return ENCODING_TYPE_GBK;
}
 
// 设置text/html 文本类型
 
public static String CONTENT_TYPE_TextHtml() {
return CONTENT_TYPE_TextHtml;
}
 
// GET
public static String GET() {
return GET;
}
 
// POST
public static String POST() {
return POST;
}
 
// MD5
public static String ENCRYPT_TYPE_MD5() {
return ENCRYPT_TYPE_MD5;
}
 
// sha1
public static String ENCRYPT_TYPE_SHA1() {
return ENCRYPT_TYPE_SHA1;
}
 
}
 
/*******************************User常量列表*********************************/
/**
 * User 存放和User类相关的常量
 ***/
public static final class User {
 
private static final String USER_IN_SESSION = "user_in_session";
private static final String USER_NAME = "username";
 
// 私有
private User() {
super();
}
 
//
public static String USER_IN_SESSION() {
return USER_IN_SESSION;
}
 
//
public static String USER_NAME() {
return USER_NAME;
}
}
 
}

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