Java SE -类的初始化顺序

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 stub
		Person 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 stub
		Person 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 stub
		Person 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