Java實例域初始化方式

1.構造器

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.域聲明

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.初始化塊（initialization block）

public class Employee { private String name; private String gender; private int age; private double salary; private static String test; //靜態初始化塊：類第一次被加載時執行 static { System.out.println('類加載'); test = 'hello world!' } //初始化塊 { 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實例域初始化順序

調用構造方法的具體處理步驟：

1. 如果類是第一次被使用，先執行靜態初始化塊

2. 所有數據域被初始化為默認值（0、false或null）

3. 按照在類聲明中出現的次序，依次執行所有域初始化語句和初始化塊。

4. 如果構造方法調用了其他構造方法，先執行其他方法。

5. 最后，執行構造方法。

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