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;
}
}
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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;
}
}
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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());
}
}
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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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