Kotlin Data Class

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Kotlin Data Class

Kotlin源码，简单的Student.kt类

data class Student(val name: String, val age: Int?= null)

使用命令javap -c Student.class反解析class文件，得到Student.class的编译的代码。对于name域，因为不可为空，所以有checkParameterIsNotNull方法进行判空检查。

Compiled from "Student.kt"public final class Student {  public final java.lang.String getName();//生成的获取name的函数  public final java.lang.Integer getAge();//生成的获取age的函数  public Student(java.lang.String, java.lang.Integer);//初始化函数    Code:       0: aload_1       1: ldc           #23                 // String name       3: invokestatic  #29                 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V//内部检查name域是否为null       6: aload_0       7: invokespecial #32                 // Method java/lang/Object."<init>":()V      10: aload_0      11: aload_1      12: putfield      #11                 // Field name:Ljava/lang/String;      15: aload_0      16: aload_2      17: putfield      #20                 // Field age:Ljava/lang/Integer;      20: return  public Student(java.lang.String, java.lang.Integer, int, kotlin.jvm.internal.DefaultConstructorMarker);//默认构造函数    Code:       0: iload_3       1: iconst_2       2: iand       3: ifeq          11       6: aconst_null       7: checkcast     #35                 // class java/lang/Integer      10: astore_2      11: aload_0      12: aload_1      13: aload_2      14: invokespecial #37                 // Method "<init>":(Ljava/lang/String;Ljava/lang/Integer;)V      17: return  public final java.lang.String component1();//从Code里看出这是获取name的，但是为啥有这个函数呢？    Code:       0: aload_0       1: getfield      #11                 // Field name:Ljava/lang/String;       4: areturn  public final java.lang.Integer component2();//从Code里看出这是获取age的，但是为啥有这个函数呢？    Code:       0: aload_0       1: getfield      #20                 // Field age:Ljava/lang/Integer;       4: areturn  public final Student copy(java.lang.String, java.lang.Integer);  public static Student copy$default(Student, java.lang.String, java.lang.Integer, int, java.lang.Object);  public java.lang.String toString();  ...  public int hashCode();  ...  public boolean equals(java.lang.Object);  ...}

修改Student.kt，增加sex域，同时提供默认值

data class Student(val name: String, var age: Int?= null, val sex: String = "Male")

反编译的代码。对于val域，由于是不可修改的，所以只有get方法。而var域则可以修改，所以有set方法。

Compiled from "Student.kt"public final class Student {  public final java.lang.String getName();  public final java.lang.Integer getAge();  public final void setAge(java.lang.Integer);  public final java.lang.String getSex();  public Student(java.lang.String, java.lang.Integer, java.lang.String);    Code:       0: aload_1       1: ldc           #30                 // String name       3: invokestatic  #36                 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V       6: aload_3       7: ldc           #37                 // String sex       9: invokestatic  #36                 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V      12: aload_0      13: invokespecial #40                 // Method java/lang/Object."<init>":()V      16: aload_0      17: aload_1      18: putfield      #11                 // Field name:Ljava/lang/String;      21: aload_0      22: aload_2      23: putfield      #20                 // Field age:Ljava/lang/Integer;      26: aload_0      27: aload_3      28: putfield      #27                 // Field sex:Ljava/lang/String;      31: return  public Student(java.lang.String, java.lang.Integer, java.lang.String, int, kotlin.jvm.internal.DefaultConstructorMarker);    Code:       0: iload         4       2: iconst_2       3: iand       4: ifeq          12       7: aconst_null       8: checkcast     #43                 // class java/lang/Integer      11: astore_2      12: iload         4      14: iconst_4      15: iand      16: ifeq          22      19: ldc           #45                 // String Male //sex域的默认值      21: astore_3      22: aload_0      23: aload_1      24: aload_2      25: aload_3      26: invokespecial #47                 // Method "<init>":(Ljava/lang/String;Ljava/lang/Integer;Ljava/lang/String;)V      29: return  public final java.lang.String component1();    Code:       0: aload_0       1: getfield      #11                 // Field name:Ljava/lang/String;       4: areturn  public final java.lang.Integer component2();    Code:       0: aload_0       1: getfield      #20                 // Field age:Ljava/lang/Integer;       4: areturn  public final java.lang.String component3();    Code:       0: aload_0       1: getfield      #27                 // Field sex:Ljava/lang/String;       4: areturn  public final Student copy(java.lang.String, java.lang.Integer, java.lang.String);  public static Student copy$default(Student, java.lang.String, java.lang.Integer, java.lang.String, int, java.lang.Object);  public java.lang.String toString();  public int hashCode();  public boolean equals(java.lang.Object);}

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