1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
| void main() {
Person person = Person('junech', 23);
print(person.toString());
Student student = Student('北大', 'tom', 23);
print(student.toString());
Student student1 = Student.cover(student);
print('student1: ${student1.toString()}');
Student student2 = Student.stu(student);
print('student2: ${student2.toString()}');
Logger logger1 = Logger();
Logger logger2 = Logger();
print('logger1 == logger2 ${logger1 == logger2}');
}
//都继承自Object
class Person {
String? name;
int? age;
Person(this.name, this.age);
@override
String toString() {
return 'name: $name age:$age';
}
}
//构造方法初始化列表
class Student extends Person {
String? _school;
String? city;
String? county;
String? funName;
//为私有变量设置 get/set方法
String? get school => _school;
set school(String? value) {
_school = value;
}
//构造方法：
//this._school 初始化自有参数
//name,age 交给父类进行初始化
//city 为可选参数
//county 设为默认值
Student(this._school, String? name, int? age,
{this.city, this.county = 'china'})
: funName = '$county.$city',
super(name, age) {
//构造方法体不是必须的
}
//命名构造方法：
//类名 + . + 方法名
//通过命名构造方法可以为类实现多个构造方法
Student.cover(Student stu) : super(stu.name, stu.age) {
print('命名构造方法');
}
//命名工厂构造方法：
//factory 类名 . 方法名
//可以有返回值，而且不需要将类的final 变量作为参数，可以灵活获取类的对象
factory Student.stu(Student st) {
return Student(st._school, st.name, st.age);
}
@override
String toString() {
return 'name: $name age:$age school:$_school city:$city county:$county';
}
}
////////////////////////////////////////////////////////////////
//抽象类:
//1、不能实例化
//2、其作用用于定义接口
//3、抽象类中也有一些实现
abstract class Study {
void study();
void study2() {
print('抽象类');
}
}
//抽象类既可以继承也可以实现
//实现的时候必须是实现抽象类中所有方法
class StudyFlutter extends Study {
@override
void study() {}
}
class StudyDart implements Study {
@override
void study() {}
@override
void study2() {}
}
////////////////////////////////////////////////////////////////
//工厂构造方法
//单例
class Logger {
static Logger? _cache;
factory Logger() {
_cache ??= Logger._internal();
return _cache!;
}
//是一个私有构造函数，用于在类内部创建 Logger 实例
Logger._internal();
}
|