Java 初始化字段方式和顺序

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Java 初始化字段方式和顺序：

类加载时直接初始化静态字段;
类加载时调用静态方法初始化静态字段;
实例化对象时,在调用构造函数之前代码块中初始化字段;
实例化对象时,在调用构造函数之时初始化字段;

　　初始化字段顺序1->2->3->4

代码如下：

public class Employee {//实例化对象时,在调用构造函数之前前初始化字段;    private int id; // 实例化对象时初始化为0    private String name; // 实例化对象时初始化为null    private boolean flag; // 实例化对象时初始化为false    private static int age = 22; // 加载类时初始化为22    // 在构造函数之前初始化    {        int num = 1111; // 实例化对象时初始化为1111        String name = "QA";// 实例化对象时初始化为QA        setId(num); // 实例化对象时调用        SetName(name); // 实例化对象时调用        System.out.println("call instance method");    }//类加载时调用静态方法初始化静态字段;    static {        System.out.println("age is: " + age);        age = 30; // 加载类时初始化为33        print(); // 加载类时时调用    }    public void SetName(String name) {        this.name = name;    }    public int getId() {        return id;    }    public String getName() {        return name;    }    public static int getAge() {        return age;    }    public void setId(int num) {        id = num;    }    public static void print() {        System.out.println("call static method");    }    public Employee() {        // TODO Auto-generated constructor stub    }    public Employee(int id, String name) {        // TODO Auto-generated constructor stub        this.id = id;        this.name = name;        System.out.println("call constructor method");    }    public static void main(String[] args) {        // TODO Auto-generated method stub        System.out.println("---------------------------");        System.out.println("age is: " + Employee.getAge());        System.out.println("---------------------------");        Employee e = new Employee();        System.out.println("id is: " + e.getId());        System.out.println("name is: " + e.getName());        System.out.println("---------------------------");        Employee e2 = new Employee(2222, "Dev");        System.out.println("id is: " + e2.getId());        System.out.println("name is: " + e2.getName());    }}

运行结果：

age is: 22

call static method

---------------------------

age is: 30

---------------------------

call instance method

id is: 1111

name is: QA

---------------------------

call instance method

call constructor method

id is: 2222

name is: Dev

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