类的初始化顺序

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类的初始化顺序为：

1：static成员变量默认初始化

2：静态块初始化

3：实例成员变量默认初始化

4：实例块初始化

5：构造函数

分析在组合关下，不同情况的初始化顺序：

<1> 在Person的构造函数中对Data进行初始化

class Data{        private int year;        private int month;        private int day;        static{            System.out.println("Data 静态初始化块");        }        {            System.out.println("Data 实例初始化块");        }        public Data(int y,int m,int d){            this.year = y;            this.month = m;            this.day = d;            System.out.println("Data 构造函数");        }}class Person{        private String name;        private int age;        private static int count;        private Data data;                static{            System.out.println("Person 静态初始化块");        }        {            System.out.println("Person 实例初始化块");        }        public Person(){            System.out.println("Person 构造函数");            data = new Data(2017,1,1);        }}public class Main {public static void main(String[] args) {// TODO Auto-generated method stubPerson p1=new Person();}}

代码运行的结果：


Person 静态初始化块
Person 实例初始化块
Person 构造函数
Data 静态初始化块
Data 实例初始化块
Data 构造函数

<2>:Data为Person的实例成员变量初始化顺序

class Data{        private int year;        private int month;        private int day;        static{            System.out.println("Data 静态初始化块");        }        {            System.out.println("Data 实例初始化块");        }        public Data(int y,int m,int d){            this.year = y;            this.month = m;            this.day = d;            System.out.println("Data 构造函数");        }}class Person{        private String name;        private int age;        private static int count;        private Data data=new Data(2017,11,16);                static{            System.out.println("Person 静态初始化块");        }        {            System.out.println("Person 实例初始化块");        }        public Person(){            System.out.println("Person 构造函数");            //data = new Data(2017,1,1);        }}public class Main {public static void main(String[] args) {// TODO Auto-generated method stubPerson p1=new Person();}}

程序运行的结果：

Person 静态初始化块
Data 静态初始化块
Data 实例初始化块
Data 构造函数
Person 实例初始化块
Person 构造函数

<3>Data为Person的静态成员变量初始化顺序：

class Data{        private int year;        private int month;        private int day;        static{            System.out.println("Data 静态初始化块");        }        {            System.out.println("Data 实例初始化块");        }        public Data(int y,int m,int d){            this.year = y;            this.month = m;            this.day = d;            System.out.println("Data 构造函数");        }}class Person{        private String name;        private int age;        private static int count;        private static Data data=new Data(2017,11,16);                static{            System.out.println("Person 静态初始化块");        }        {            System.out.println("Person 实例初始化块");        }        public Person(){            System.out.println("Person 构造函数");            //data = new Data(2017,1,1);        }}public class Main {public static void main(String[] args) {// TODO Auto-generated method stubPerson p1=new Person();}}

运行结果：

Data 静态初始化块
Data 实例初始化块
Data 构造函数
Person 静态初始化块
Person 实例初始化块
Person 构造函数

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