Kotlin静态和常量值&方法声明

object MyConstant {

@JvmField   // for access in java code 
val PI: Double = 3.14

@JvmStatic // JvmStatic annotation for access in java code
fun sumValue(v1: Int, v2: Int): Int {
    return v1 + v2
}

}

在任何地方访问值

val value = MyConstant.PI
val value = MyConstant.sumValue(10,5)

我认为这将是把一个包的所有常量放在同一个文件中的最好方法，正如在其他答案中提到的，这避免了创建伴侣对象，这使得这个性能和非常类似于Java constants类。

class Constants {
    object Analytics {
        const val PROJECT_OPEN = "project_open"
        const val PROJECT_CLOSE = "project_close"
    }

    object HTTP {
        const val BASE_URL = "x.y.com"
    }

    object DBConst {
        const val TABLE_NAME = "abc"
    }
}

这可以从这样的代码中引用，使其非常结构化。

Constants.Analytics.PROJECT_OPEN
Constants.HTTP.BASE_URL
Constants.DBConst.TABLE_NAME

Kotlin静态和常量值&方法声明

object MyConstant {

@JvmField   // for access in java code 
val PI: Double = 3.14

@JvmStatic // JvmStatic annotation for access in java code
fun sumValue(v1: Int, v2: Int): Int {
    return v1 + v2
}

}

在任何地方访问值

val value = MyConstant.PI
val value = MyConstant.sumValue(10,5)

避免使用伴随对象。在底层，为可访问的字段创建了getter和setter实例方法。从技术上讲，调用实例方法比调用静态方法代价更大。

public class DbConstants {
    companion object {
        val TABLE_USER_ATTRIBUTE_EMPID = "_id"
        val TABLE_USER_ATTRIBUTE_DATA = "data"
    }

而是在object中定义常量。

推荐的做法:

object DbConstants {
    const val TABLE_USER_ATTRIBUTE_EMPID = "_id"
    const val TABLE_USER_ATTRIBUTE_DATA = "data"
}

并像这样全局访问它们: DbConstants。TABLE_USER_ATTRIBUTE_EMPID

如果你把const val valName = valValue放在类名之前，这样就会创建一个

public static final YourClass。Kt会有公共的静态最终值。

科特林：

const val MY_CONST0 = 0
const val MY_CONST1 = 1
data class MyClass(var some: String)

Java反编译:

public final class MyClassKt {
    public static final int MY_CONST0 = 0;
    public static final int MY_CONST1 = 1;
}
// rest of MyClass.java

对于基元和字符串:

/** The empty String. */
const val EMPTY_STRING = ""

其他情况:

/** The empty array of Strings. */
@JvmField val EMPTY_STRING_ARRAY = arrayOfNulls<String>(0)

例子:

/*
 * Copyright 2018 Vorlonsoft LLC
 *
 * Licensed under The MIT License (MIT)
 */

package com.vorlonsoft.android.rate

import com.vorlonsoft.android.rate.Constants.Utils.Companion.UTILITY_CLASS_MESSAGE

/**
 * Constants Class - the constants class of the AndroidRate library.
 *
 * @constructor Constants is a utility class and it can't be instantiated.
 * @since       1.1.8
 * @version     1.2.1
 * @author      Alexander Savin
 */
internal class Constants private constructor() {
    /** Constants Class initializer block. */
    init {
        throw UnsupportedOperationException("Constants$UTILITY_CLASS_MESSAGE")
    }

    /**
     * Constants.Date Class - the date constants class of the AndroidRate library.
     *
     * @constructor Constants.Date is a utility class and it can't be instantiated.
     * @since       1.1.8
     * @version     1.2.1
     * @author      Alexander Savin
     */
    internal class Date private constructor() {
        /** Constants.Date Class initializer block. */
        init {
            throw UnsupportedOperationException("Constants.Date$UTILITY_CLASS_MESSAGE")
        }

        /** The singleton contains date constants. */
        companion object {
            /** The time unit representing one year in days. */
            const val YEAR_IN_DAYS = 365.toShort()
        }
    }

    /**
     * Constants.Utils Class - the utils constants class of the AndroidRate library.
     *
     * @constructor Constants.Utils is a utility class and it can't be instantiated.
     * @since       1.1.8
     * @version     1.2.1
     * @author      Alexander Savin
     */
    internal class Utils private constructor() {
        /** Constants.Utils Class initializer block. */
        init {
            throw UnsupportedOperationException("Constants.Utils$UTILITY_CLASS_MESSAGE")
        }

        /** The singleton contains utils constants. */
        companion object {
            /** The empty String. */
            const val EMPTY_STRING = ""
            /** The empty array of Strings. */
            @JvmField val EMPTY_STRING_ARRAY = arrayOfNulls<String>(0)
            /** The part 2 of a utility class unsupported operation exception message. */
            const val UTILITY_CLASS_MESSAGE = " is a utility class and it can't be instantiated!"
        }
    }
}