kotlin 对比 java
| 维度 | Kotlin | Java |
|---|---|---|
| 语法简洁性 | ✅ 更简洁（支持类型推导、默认参数等） | ❌ 相对繁琐（代码冗长） |
| 空指针安全 | ✅ 内建 Null 安全系统 | ❌ Null 是常见错误来源 |
| 扩展函数支持 | ✅ 支持 | ❌ 不支持 |
| 协程支持 | ✅ 内置协程（轻量线程） | ❌ 需要使用线程或第三方库 |
| Lambda 表达式 | ✅ 原生支持 | ✅ Java 8+ 开始支持 |
| 数据类 | ✅ 内建 data class |
❌ 手写 getter、setter 等 |
| 默认不可变性 | ✅ 推荐使用 val | ❌ 默认可变 |
| 类型推导 | ✅ 支持类型自动推导 | ❌ 必须声明类型 |
| 枚举增强 | ✅ 支持密封类、when | ❌ 功能有限 |
| Android 支持 | ✅ 官方推荐语言 | ✅ 老牌稳定语言 |
| JVM 兼容性 | ✅ 与 Java 完全互通 | ✅ 与 Kotlin 可互通（公开 API） |
| 编译速度 | ⏳ 稍慢 | ⚡ 更快 |
| 学习曲线 | ⬆️ 稍陡峭 | ✅ 容易上手 |
| 社区生态 | ✅ 活跃增长中 | ✅ 非常成熟 |
build.gradle 和 build.gradle.kts
| 特性 | Groovy (build.gradle) |
Kotlin (build.gradle.kts) |
|---|---|---|
| 类型安全 | ❌ 弱类型 | ✅ 强类型 |
| 自动补全与提示 | ❌ 弱 | ✅ 好（尤其在 Android Studio Arctic Fox+） |
| 脚本灵活性 | ✅ 高（支持较多 DSL 魔法） | ⚠️ 限制较多，语法更严格 |
| 编写易用性 | ✅ 语法宽松 | ⚠️ 容易踩坑，尤其是早期版本 Gradle 插件 |
| 编译性能 | ⚠️ 稍慢 | ✅ 稍快（Gradle 7.0+ 表现更佳） |
| 官方趋势 | ✅ 兼容主流项目 | ✅ Google 已推荐新项目使用 Kotlin DSL |
settings.gradle.kts
pluginManagement {
repositories {
google()
maven {
url = uri("https://maven.aliyun.com/repository/gradle-plugin")
content {
includeGroupByRegex("com\\.android.*")
includeGroupByRegex("com\\.google.*")
includeGroupByRegex("androidx.*")
}
}
mavenCentral()
gradlePluginPortal()
}
}
dependencyResolutionManagement {
repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
repositories {
maven { url = uri("https://maven.aliyun.com/repository/public") }
maven { url = uri("https://maven.aliyun.com/repository/google") }
maven { url = uri("https://maven.aliyun.com/repository/jcenter") } // 已经废弃，仅用于老项目
google()
mavenCentral()
}
}
rootProject.name = "AccessibilityDemo"
include(":app")
build.gradle.kts
// Top-level build file where you can add configuration options common to all sub-projects/modules.
plugins {
alias(libs.plugins.android.application) apply false
alias(libs.plugins.kotlin.android) apply false
alias(libs.plugins.kotlin.compose) apply false
}
app/build.gradle.kts
plugins {
alias(libs.plugins.android.application)
alias(libs.plugins.kotlin.android)
alias(libs.plugins.kotlin.compose)
}
android {
namespace = "com.wif.demo"
compileSdk = 35
defaultConfig {
applicationId = "com.wif.demo"
minSdk = 24
targetSdk = 35
versionCode = 1
versionName = "1.0"
testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
isMinifyEnabled = false
proguardFiles(
getDefaultProguardFile("proguard-android-optimize.txt"),
"proguard-rules.pro"
)
}
}
compileOptions {
sourceCompatibility = JavaVersion.VERSION_11
targetCompatibility = JavaVersion.VERSION_11
}
kotlinOptions {
jvmTarget = "11"
}
buildFeatures {
compose = true
}
}
dependencies {
implementation(libs.androidx.core.ktx)
implementation(libs.androidx.lifecycle.runtime.ktx)
implementation(libs.androidx.activity.compose)
implementation(platform(libs.androidx.compose.bom))
implementation(libs.androidx.ui)
implementation(libs.androidx.ui.graphics)
implementation(libs.androidx.ui.tooling.preview)
implementation(libs.androidx.material3)
testImplementation(libs.junit)
androidTestImplementation(libs.androidx.junit)
androidTestImplementation(libs.androidx.espresso.core)
androidTestImplementation(platform(libs.androidx.compose.bom))
androidTestImplementation(libs.androidx.ui.test.junit4)
debugImplementation(libs.androidx.ui.tooling)
debugImplementation(libs.androidx.ui.test.manifest)
}
gradle/libs.versions.toml
[versions]
agp = "8.10.1"
kotlin = "2.0.21"
coreKtx = "1.10.1"
junit = "4.13.2"
junitVersion = "1.1.5"
espressoCore = "3.5.1"
lifecycleRuntimeKtx = "2.6.1"
activityCompose = "1.8.0"
composeBom = "2024.09.00"
[libraries]
androidx-core-ktx = { group = "androidx.core", name = "core-ktx", version.ref = "coreKtx" }
junit = { group = "junit", name = "junit", version.ref = "junit" }
androidx-junit = { group = "androidx.test.ext", name = "junit", version.ref = "junitVersion" }
androidx-espresso-core = { group = "androidx.test.espresso", name = "espresso-core", version.ref = "espressoCore" }
androidx-lifecycle-runtime-ktx = { group = "androidx.lifecycle", name = "lifecycle-runtime-ktx", version.ref = "lifecycleRuntimeKtx" }
androidx-activity-compose = { group = "androidx.activity", name = "activity-compose", version.ref = "activityCompose" }
androidx-compose-bom = { group = "androidx.compose", name = "compose-bom", version.ref = "composeBom" }
androidx-ui = { group = "androidx.compose.ui", name = "ui" }
androidx-ui-graphics = { group = "androidx.compose.ui", name = "ui-graphics" }
androidx-ui-tooling = { group = "androidx.compose.ui", name = "ui-tooling" }
androidx-ui-tooling-preview = { group = "androidx.compose.ui", name = "ui-tooling-preview" }
androidx-ui-test-manifest = { group = "androidx.compose.ui", name = "ui-test-manifest" }
androidx-ui-test-junit4 = { group = "androidx.compose.ui", name = "ui-test-junit4" }
androidx-material3 = { group = "androidx.compose.material3", name = "material3" }
[plugins]
android-application = { id = "com.android.application", version.ref = "agp" }
kotlin-android = { id = "org.jetbrains.kotlin.android", version.ref = "kotlin" }
kotlin-compose = { id = "org.jetbrains.kotlin.plugin.compose", version.ref = "kotlin" }
关系图
libs.versions.toml
│
└──▶ 提供版本号和别名（比如 agp、kotlin、compose）
│
▼
settings.gradle.kts
├── 设置插件仓库 pluginManagement { ... }
├── 设置依赖仓库 dependencyResolutionManagement { ... }
└── include(":app") 指定模块
│
▼
build.gradle.kts（每个模块）
├── 使用 plugins { alias(...) } 引入插件
└── 使用 dependencies { implementation(...) } 引入依赖
基本语法
- 变量 val var
- 运算符 与java一致
- 字符串
- 字符串操作函数
- 模板表达式
- 条件语句
- when 字符，kotlin没有switch关键字
- 循环语句 while for
- 跳转语句 continue break
- 区间
- 数组
- 变量的类型转换
- 可空变量 非空变量
- ?: 操作符
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val int_a: Int = 1
val Str_a: String = "hello"
Log.d("LXG", Str_a)
Log.d("LXG", "" + Str_a[3])
val number: IntArray = intArrayOf(1, 2, 3, 4)
var bool_array: BooleanArray = booleanArrayOf(true, true, false)
var char_array: CharArray = charArrayOf('a', 'b')
val int_array: Array<Int> = arrayOf(1, 2, 3)
var string_array: Array<String> = arrayOf("hello", "world")
var num1 = 1
val s1 = "a is ${num1}"
val s2 = "a is $num1"
Log.d("LXG", "" + s1)
Log.d("LXG", "" + s2)
var month: Int = 7
when(month) {
12,1,2 -> println("冬季")
3,4,5 -> println("春季")
6,7,8 -> println("夏季")
9,10,11 -> println("秋季")
else -> println("未知")
}
var a: Int = 7
var b: Int = 8
when {
a > b -> println("a 大于 b")
a < b -> println("a 大于 b")
else -> println("a 等于 b")
}
for (i in 0..3) {
println("i = $i")
}
number.forEach { println(it.toString() + "\t") }
string_array.forEachIndexed() {index, s -> println("index = $index , s = $s") }
// 区间
for (i in 1.rangeTo(4)) {
println("i = $i")
}
for (i in 4.downTo(1)) {
println("i = $i")
}
for (i in 4.downTo(1) step 2) {
println("i = $i")
}
// 数组
for ((index, i) in bool_array.withIndex()) {
println("index = $index , s = $i")
}
println("4, index = " + number.indexOf(4))
var name: String = "Tom" // 非空变量
var telephone : String? = null
var result = telephone?.length
println(result)
}
