1.数据类
数据类 -- data class：类似于java中的实体类，与数据库映射的类。如：领域模型、domain、model等。
数据类需要满足如下要求：
①主构造方法至少要有一个参数。
②所有的主构造方法参数都需要被标记为var或者是val。
③数据类不能是抽象的、open、sealed的以及inner。
对于数据类，编译器会自动生成如下内容：
①equals/hashCode对。
②toString()方法，形式为Person(name=...,age=...,address=...)
③针对属性的componentN方法，并且是按照属性的声明顺序来生成的。
- 示例代码
data class Person(val name: String, var age: Int, var address: String)
fun main(args: Array<String>) {
var person = Person("zhangsan",20,"beijing")
println(person)
}
- 输出结果
Person(name=zhangsan, age=20, address=beijing)
- 反编译Person
➜ kotlin_lecture javap -c com.leofight.kotlin2.Person
Compiled from "HelloKotlin1.kt"
public final class com.leofight.kotlin2.Person {
public final java.lang.String getName();
Code:
0: aload_0
1: getfield #11 // Field name:Ljava/lang/String;
4: areturn
public final int getAge();
Code:
0: aload_0
1: getfield #19 // Field age:I
4: ireturn
public final void setAge(int);
Code:
0: aload_0
1: iload_1
2: putfield #19 // Field age:I
5: return
public final java.lang.String getAddress();
Code:
0: aload_0
1: getfield #26 // Field address:Ljava/lang/String;
4: areturn
public final void setAddress(java.lang.String);
Code:
0: aload_1
1: ldc #29 // String <set-?>
3: invokestatic #35 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V
6: aload_0
7: aload_1
8: putfield #26 // Field address:Ljava/lang/String;
11: return
public com.leofight.kotlin2.Person(java.lang.String, int, java.lang.String);
Code:
0: aload_1
1: ldc #38 // String name
3: invokestatic #35 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V
6: aload_3
7: ldc #39 // String address
9: invokestatic #35 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V
12: aload_0
13: invokespecial #42 // Method java/lang/Object."<init>":()V
16: aload_0
17: aload_1
18: putfield #11 // Field name:Ljava/lang/String;
21: aload_0
22: iload_2
23: putfield #19 // Field age:I
26: aload_0
27: aload_3
28: putfield #26 // Field address:Ljava/lang/String;
31: return
public final java.lang.String component1();
Code:
0: aload_0
1: getfield #11 // Field name:Ljava/lang/String;
4: areturn
public final int component2();
Code:
0: aload_0
1: getfield #19 // Field age:I
4: ireturn
public final java.lang.String component3();
Code:
0: aload_0
1: getfield #26 // Field address:Ljava/lang/String;
4: areturn
public final com.leofight.kotlin2.Person copy(java.lang.String, int, java.lang.String);
Code:
0: aload_1
1: ldc #38 // String name
3: invokestatic #35 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V
6: aload_3
7: ldc #39 // String address
9: invokestatic #35 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V
12: new #2 // class com/leofight/kotlin2/Person
15: dup
16: aload_1
17: iload_2
18: aload_3
19: invokespecial #49 // Method "<init>":(Ljava/lang/String;ILjava/lang/String;)V
22: areturn
public static com.leofight.kotlin2.Person copy$default(com.leofight.kotlin2.Person, java.lang.String, int, java.lang.String, int, java.lang.Object);
Code:
0: iload 4
2: iconst_1
3: iand
4: ifeq 12
7: aload_0
8: getfield #11 // Field name:Ljava/lang/String;
11: astore_1
12: iload 4
14: iconst_2
15: iand
16: ifeq 24
19: aload_0
20: getfield #19 // Field age:I
23: istore_2
24: iload 4
26: iconst_4
27: iand
28: ifeq 36
31: aload_0
32: getfield #26 // Field address:Ljava/lang/String;
35: astore_3
36: aload_0
37: aload_1
38: iload_2
39: aload_3
40: invokevirtual #53 // Method copy:(Ljava/lang/String;ILjava/lang/String;)Lcom/leofight/kotlin2/Person;
43: areturn
public java.lang.String toString();
Code:
0: new #56 // class java/lang/StringBuilder
3: dup
4: invokespecial #57 // Method java/lang/StringBuilder."<init>":()V
7: ldc #59 // String Person(name=
9: invokevirtual #63 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
12: aload_0
13: getfield #11 // Field name:Ljava/lang/String;
16: invokevirtual #63 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
19: ldc #65 // String , age=
21: invokevirtual #63 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
24: aload_0
25: getfield #19 // Field age:I
28: invokevirtual #68 // Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder;
31: ldc #70 // String , address=
33: invokevirtual #63 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
36: aload_0
37: getfield #26 // Field address:Ljava/lang/String;
40: invokevirtual #63 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
43: ldc #72 // String )
45: invokevirtual #63 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
48: invokevirtual #74 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
51: areturn
public int hashCode();
Code:
0: aload_0
1: getfield #11 // Field name:Ljava/lang/String;
4: dup
5: ifnull 14
8: invokevirtual #77 // Method java/lang/Object.hashCode:()I
11: goto 16
14: pop
15: iconst_0
16: bipush 31
18: imul
19: aload_0
20: getfield #19 // Field age:I
23: invokestatic #82 // Method java/lang/Integer.hashCode:(I)I
26: iadd
27: bipush 31
29: imul
30: aload_0
31: getfield #26 // Field address:Ljava/lang/String;
34: dup
35: ifnull 44
38: invokevirtual #77 // Method java/lang/Object.hashCode:()I
41: goto 46
44: pop
45: iconst_0
46: iadd
47: ireturn
public boolean equals(java.lang.Object);
Code:
0: aload_0
1: aload_1
2: if_acmpeq 64
5: aload_1
6: instanceof #2 // class com/leofight/kotlin2/Person
9: ifeq 66
12: aload_1
13: checkcast #2 // class com/leofight/kotlin2/Person
16: astore_2
17: aload_0
18: getfield #11 // Field name:Ljava/lang/String;
21: aload_2
22: getfield #11 // Field name:Ljava/lang/String;
25: invokestatic #90 // Method kotlin/jvm/internal/Intrinsics.areEqual:(Ljava/lang/Object;Ljava/lang/Object;)Z
28: ifeq 66
31: aload_0
32: getfield #19 // Field age:I
35: aload_2
36: getfield #19 // Field age:I
39: if_icmpne 46
42: iconst_1
43: goto 47
46: iconst_0
47: ifeq 66
50: aload_0
51: getfield #26 // Field address:Ljava/lang/String;
54: aload_2
55: getfield #26 // Field address:Ljava/lang/String;
58: invokestatic #90 // Method kotlin/jvm/internal/Intrinsics.areEqual:(Ljava/lang/Object;Ljava/lang/Object;)Z
61: ifeq 66
64: iconst_1
65: ireturn
66: iconst_0
67: ireturn
}
关于数据类成员的继承要点：
①如果数据类中显式定义了equals，hashCode或是toString方法，或者是在数据类的父类中将这些方法声明为了final，那么这些方法就不会再生成，转而使用已有的。
②如果父类拥有componentN方法，并且是open的以及返回兼容的类型，那么编译器就会在数据类中生成相应的componentN方法，并且重写父类的这些方法；如果父类中的这些方法由于不兼容的签名或者定义为final的，那么编译器就会报错。
③在数据类中显式提供componentN方法以及copy方法实现是不允许的。
解构声明
在主构造方法中又多少个参数，就会依次生成对应的component1、component2、component3...这些方法返回的就是对应字段的值，componentN方法是用来实现解构声明的。
- 示例代码
data class Person(val name: String, var age: Int, var address: String){
}
fun main(args: Array<String>) {
var person = Person("zhangsan",20,"beijing")
println(person)
person.age = 30
println(person.age)
var person2 = person.copy(address = "hangzhou")
println(person2)
//解构
var (name,age,address) = person
println("$name,$age,$address")
}
- 运行结果
Person(name=zhangsan, age=20, address=beijing)
30
Person(name=zhangsan, age=30, address=hangzhou)
zhangsan,30,beijing
在JVM平台上，如果生成的类需要拥有无参构造方法，那么就需要为所有属性指定默认值。
- 示例代码
data class Person2(val name:String = "",var age: Int = 20, var address: String = "tianjing")
- 反编译Person2
➜ kotlin_lecture javap -c com.leofight.kotlin2.Person2
Compiled from "HelloKotlin1.kt"
public final class com.leofight.kotlin2.Person2 {
public final java.lang.String getName();
Code:
0: aload_0
1: getfield #11 // Field name:Ljava/lang/String;
4: areturn
public final int getAge();
Code:
0: aload_0
1: getfield #19 // Field age:I
4: ireturn
public final void setAge(int);
Code:
0: aload_0
1: iload_1
2: putfield #19 // Field age:I
5: return
public final java.lang.String getAddress();
Code:
0: aload_0
1: getfield #26 // Field address:Ljava/lang/String;
4: areturn
public final void setAddress(java.lang.String);
Code:
0: aload_1
1: ldc #29 // String <set-?>
3: invokestatic #35 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V
6: aload_0
7: aload_1
8: putfield #26 // Field address:Ljava/lang/String;
11: return
public com.leofight.kotlin2.Person2(java.lang.String, int, java.lang.String);
Code:
0: aload_1
1: ldc #38 // String name
3: invokestatic #35 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V
6: aload_3
7: ldc #39 // String address
9: invokestatic #35 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V
12: aload_0
13: invokespecial #42 // Method java/lang/Object."<init>":()V
16: aload_0
17: aload_1
18: putfield #11 // Field name:Ljava/lang/String;
21: aload_0
22: iload_2
23: putfield #19 // Field age:I
26: aload_0
27: aload_3
28: putfield #26 // Field address:Ljava/lang/String;
31: return
public com.leofight.kotlin2.Person2(java.lang.String, int, java.lang.String, int, kotlin.jvm.internal.DefaultConstructorMarker);
Code:
0: iload 4
2: iconst_1
3: iand
4: ifeq 10
7: ldc #45 // String
9: astore_1
10: iload 4
12: iconst_2
13: iand
14: ifeq 20
17: bipush 20
19: istore_2
20: iload 4
22: iconst_4
23: iand
24: ifeq 30
27: ldc #47 // String tianjing
29: astore_3
30: aload_0
31: aload_1
32: iload_2
33: aload_3
34: invokespecial #49 // Method "<init>":(Ljava/lang/String;ILjava/lang/String;)V
37: return
public com.leofight.kotlin2.Person2();
Code:
0: aload_0
1: aconst_null
2: iconst_0
3: aconst_null
4: bipush 7
6: aconst_null
7: invokespecial #51 // Method "<init>":(Ljava/lang/String;ILjava/lang/String;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
10: return
public final java.lang.String component1();
Code:
0: aload_0
1: getfield #11 // Field name:Ljava/lang/String;
4: areturn
public final int component2();
Code:
0: aload_0
1: getfield #19 // Field age:I
4: ireturn
public final java.lang.String component3();
Code:
0: aload_0
1: getfield #26 // Field address:Ljava/lang/String;
4: areturn
public final com.leofight.kotlin2.Person2 copy(java.lang.String, int, java.lang.String);
Code:
0: aload_1
1: ldc #38 // String name
3: invokestatic #35 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V
6: aload_3
7: ldc #39 // String address
9: invokestatic #35 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V
12: new #2 // class com/leofight/kotlin2/Person2
15: dup
16: aload_1
17: iload_2
18: aload_3
19: invokespecial #49 // Method "<init>":(Ljava/lang/String;ILjava/lang/String;)V
22: areturn
public static com.leofight.kotlin2.Person2 copy$default(com.leofight.kotlin2.Person2, java.lang.String, int, java.lang.String, int, java.lang.Object);
Code:
0: iload 4
2: iconst_1
3: iand
4: ifeq 12
7: aload_0
8: getfield #11 // Field name:Ljava/lang/String;
11: astore_1
12: iload 4
14: iconst_2
15: iand
16: ifeq 24
19: aload_0
20: getfield #19 // Field age:I
23: istore_2
24: iload 4
26: iconst_4
27: iand
28: ifeq 36
31: aload_0
32: getfield #26 // Field address:Ljava/lang/String;
35: astore_3
36: aload_0
37: aload_1
38: iload_2
39: aload_3
40: invokevirtual #60 // Method copy:(Ljava/lang/String;ILjava/lang/String;)Lcom/leofight/kotlin2/Person2;
43: areturn
public java.lang.String toString();
Code:
0: new #63 // class java/lang/StringBuilder
3: dup
4: invokespecial #64 // Method java/lang/StringBuilder."<init>":()V
7: ldc #66 // String Person2(name=
9: invokevirtual #70 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
12: aload_0
13: getfield #11 // Field name:Ljava/lang/String;
16: invokevirtual #70 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
19: ldc #72 // String , age=
21: invokevirtual #70 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
24: aload_0
25: getfield #19 // Field age:I
28: invokevirtual #75 // Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder;
31: ldc #77 // String , address=
33: invokevirtual #70 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
36: aload_0
37: getfield #26 // Field address:Ljava/lang/String;
40: invokevirtual #70 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
43: ldc #79 // String )
45: invokevirtual #70 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
48: invokevirtual #81 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
51: areturn
public int hashCode();
Code:
0: aload_0
1: getfield #11 // Field name:Ljava/lang/String;
4: dup
5: ifnull 14
8: invokevirtual #84 // Method java/lang/Object.hashCode:()I
11: goto 16
14: pop
15: iconst_0
16: bipush 31
18: imul
19: aload_0
20: getfield #19 // Field age:I
23: invokestatic #89 // Method java/lang/Integer.hashCode:(I)I
26: iadd
27: bipush 31
29: imul
30: aload_0
31: getfield #26 // Field address:Ljava/lang/String;
34: dup
35: ifnull 44
38: invokevirtual #84 // Method java/lang/Object.hashCode:()I
41: goto 46
44: pop
45: iconst_0
46: iadd
47: ireturn
public boolean equals(java.lang.Object);
Code:
0: aload_0
1: aload_1
2: if_acmpeq 64
5: aload_1
6: instanceof #2 // class com/leofight/kotlin2/Person2
9: ifeq 66
12: aload_1
13: checkcast #2 // class com/leofight/kotlin2/Person2
16: astore_2
17: aload_0
18: getfield #11 // Field name:Ljava/lang/String;
21: aload_2
22: getfield #11 // Field name:Ljava/lang/String;
25: invokestatic #97 // Method kotlin/jvm/internal/Intrinsics.areEqual:(Ljava/lang/Object;Ljava/lang/Object;)Z
28: ifeq 66
31: aload_0
32: getfield #19 // Field age:I
35: aload_2
36: getfield #19 // Field age:I
39: if_icmpne 46
42: iconst_1
43: goto 47
46: iconst_0
47: ifeq 66
50: aload_0
51: getfield #26 // Field address:Ljava/lang/String;
54: aload_2
55: getfield #26 // Field address:Ljava/lang/String;
58: invokestatic #97 // Method kotlin/jvm/internal/Intrinsics.areEqual:(Ljava/lang/Object;Ljava/lang/Object;)Z
61: ifeq 66
64: iconst_1
65: ireturn
66: iconst_0
67: ireturn
}
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