# Kotlin 中初始化块、初始化的顺序、lateinit延迟初始化详解

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原文：https://www.dandroid.cn/archives/19800
Canonical：https://www.dandroid.cn/archives/19800
作者：admin
发布日期：2023-09-10
最后更新：2023-09-10 06:56
分类：Kotlin
内容类型：post
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## 正文

1、初始化块：初始化块可以设置变量或值，以及执行有效性检查，如检查传给某构造函数的值是否有效，初始化块代码会在构造类实例时执行。

案例代码如下：

class Player3(
 _name: String, var age: Int = 20, var isNormal: Boolean
) {
 var name = _name
 get() = field.capitalize()
 set(value) {
 field = value.trim()
 }
 //次构造函数
 //我们可以定义多个次构造函数来配置不同的参数组合
 constructor(name: String) : this(name, age = 100, isNormal = false)
 constructor(name: String, age: Int) : this(name, age = 10, isNormal = false) {
 println("次构造函数")
 this.name = name.toUpperCase()
 }
 init {
 println("测试init")
 require(age > 0) {
 "age muse be positive"
 }
 require(name.isNotBlank()) {
 "player must have a name"
 }
 }
}
fun main() {
 val player = Player3(isNormal = false, _name = "Jack")
 println("${player.name}, ${player.age}, ${player.isNormal}")
 val p = Player3("Android", 10)
 println("${p.name},${p.age},${p.isNormal}")
}

输出结果如下：

测试init
Jack, 20, false
测试init
次构造函数
ANDROID,10,false

2.初始化执行的顺序

主构造函数里声明的属性

类级别的属性赋值

init初始块里的属性赋值和函数调用

次构造函数里的属性赋值和函数调用

案例代码如下：

class Students(
 _name: String, val age: Int
) {
 var name = _name
 var score = 10
 private val hobby = "music"
 val subject: String
 //初始化块
 init {
 println("initializing Students...")
 subject = "math"
 }
 constructor(_name: String) : this(_name, 10) {
 score = 20
 }
}
fun main() {
 Students("Jack")
}

可以通过反编译看java代码，就清楚了，反编译代码如下

public final class StudentsKt {
 public static final void main() {
 new Students("Jack");
 }
 // $FF: synthetic method
 public static void main(String[] var0) {
 main();
 }
}
// Students.java
package kotlin04;
import kotlin.Metadata;
import kotlin.jvm.internal.Intrinsics;
import org.jetbrains.annotations.NotNull;
@Metadata(
 mv = {1, 6, 0},
 k = 1,
 d1 = {"u0000u001anu0002u0018u0002nu0002u0010u0000nu0000nu0002u0010u000enu0002bu0002nu0002u0010bnu0002bu000fu0018u00002u00020u0001Bu000fbu0016u0012u0006u0010u0002u001au00020u0003¢u0006u0002u0010u0004Bu0015u0012u0006u0010u0002u001au00020u0003u0012u0006u0010u0005u001au00020u0006¢u0006u0002u0010u0007Ru0011u0010u0005u001au00020u0006¢u0006bnu0000u001au0004bbu0010tRu000eu0010nu001au00020u0003Xu0082D¢u0006u0002nu0000Ru001au0010u000bu001au00020u0003Xu0086u000e¢u0006u000enu0000u001au0004bfu0010r"u0004bu000eu0010u0004Ru001au0010u000fu001au00020u0006Xu0086u000e¢u0006u000enu0000u001au0004bu0010u0010t"u0004bu0011u0010u0012Ru0011u0010u0013u001au00020u0003¢u0006bnu0000u001au0004bu0014u0010r¨u0006u0015"},
 d2 = {"Lkotlin04/Students;", "", "_name", "", "(Ljava/lang/String;)V", "age", "", "(Ljava/lang/String;I)V", "getAge", "()I", "hobby", "name", "getName", "()Ljava/lang/String;", "setName", "score", "getScore", "setScore", "(I)V", "subject", "getSubject", "kotlinStudy"}
)
public final class Students {
 @NotNull
 private String name;
 private int score;
 private final String hobby;
 @NotNull
 private final String subject;
 private final int age;
 @NotNull
 public final String getName() {
 return this.name;
 }
 public final void setName(@NotNull String var1) {
 Intrinsics.checkNotNullParameter(var1, "");
 this.name = var1;
 }
 public final int getScore() {
 return this.score;
 }
 public final void setScore(int var1) {
 this.score = var1;
 }
 @NotNull
 public final String getSubject() {
 return this.subject;
 }
 public final int getAge() {
 return this.age;
 }
 public Students(@NotNull String _name, int age) {
 Intrinsics.checkNotNullParameter(_name, "_name");
 super();
 this.age = age;
 this.name = _name;
 this.score = 10;
 this.hobby = "music";
 String var3 = "initializing Students...";
 System.out.println(var3);
 this.subject = "math";
 }
 public Students(@NotNull String _name) {
 Intrinsics.checkNotNullParameter(_name, "_name");
 this(_name, 10);
 this.score = 20;
 }
}

3、延迟初始化lateinit

class Player4 {
 lateinit var equipment: String
 fun ready() {
 equipment = "sharp knife"
 }
 fun battle() {
 if (::equipment.isInitialized) {//该属性初始化,执行该代码
 println(equipment)
 }
 }
}
fun main() {
 val p = Player4()
 p.ready()
 p.battle()
}

输出结果

sharp knife

 

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由 答源 DAN 底座 1.4.1 生成 · 2026-11-12T23:23:52+00:00