Java实例域初始化方法及顺序

Java实例域初始化方式

1.构造器

public class Employee { private String name; private String gender; private int age; private double salary; public Employee() { this.salary = 1000.0; } public Employee(String name, String gender, int age, double salary) { this.name = name; this.gender = gender; this.age = age; this.salary = salary; }}

2.域声明

public class Employee { private String name; private String gender; private int age; private double salary = 1000.0; public Employee() { } public Employee(String name, String gender, int age, double salary) { this.name = name; this.gender = gender; this.age = age; this.salary = salary; }}

3.初始化块（initialization block）

public class Employee { private String name; private String gender; private int age; private double salary; private static String test; //静态初始化块：类第一次被加载时执行 static { System.out.println('类加载'); test = 'hello world!' } //初始化块 { name = 'xiao'; gender = 'm'; age = 20; salary = 1000.0; System.out.println('初始化'); } @Override public String toString() { return 'Employee{' +'name=’' + name + ’’’ +', gender=’' + gender + ’’’ +', age=' + age +', salary=' + salary +’}’; } public static void main(String[] args) { Employee employee = new Employee(); System.out.println(employee.toString()); }}

初始化Employee{name=’xiao’, gender=’m’, age=20, salary=1000.0}Process finished with exit code 0

Java实例域初始化顺序

调用构造方法的具体处理步骤：

1. 如果类是第一次被使用，先执行静态初始化块

2. 所有数据域被初始化为默认值（0、false或null）

3. 按照在类声明中出现的次序，依次执行所有域初始化语句和初始化块。

4. 如果构造方法调用了其他构造方法，先执行其他方法。

5. 最后，执行构造方法。

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