java对象属性的初始值

当我们创建一个实例时，如果没有在构造器中初始化非静态属性，编译器会将数值类型数据设为0，布尔类型数据设为false，对象类型数据设为null。

也可以通过一下方式初始化：

（1）在构造方法中初始化

（2）直接给属性默认值或调静态方法初始化。虽然PHP不能调静态方法初始化非静态属性，但是可以在构造方法中调静态方法初始化非静态属性

public class Employee {
    protected String name;
    protected double salary;
    protected int id = assignId();
    protected static int nextId = 1;

    protected LocalDate hireDay;

    public Employee(String name, double salary, String hireDay) {
        this.name = name;
        this.salary = salary;
        this.hireDay = LocalDate.parse(hireDay);
    }

    public Employee(String name, double salary) {
        this.name = name;
        this.salary = salary;
    }

    public String getHireDay() {
        return hireDay.format(DateTimeFormatter.ofPattern("y-MM-dd"));
    }

    public String getHireDay(String DayFormatter) {
        return hireDay.format(DateTimeFormatter.ofPattern(DayFormatter));
    }

    public String getName() {
        return name;
    }

    public int getId()
    {
        return id;
    }

    protected int assignId()
    {
        return nextId++;
    }
}