Java:继承的类构造函数正在调用Super类

Question

在创建java程序时我遇到了问题,

子类构造函数通过调用Superclass的方法抛出Error

代码类似于:

class Manage
{
    public static void main(String[] args) 
    {
        Manager m1 = new Manager ( 35 );
    }
}

class Employee
{
        int emp_id;
        public Employee(int id)
        {
                this.emp_id = id;
        }
        public int get_id()
        {
                return emp_id;
        }

}
class Manager extends Employee
{
        public Manager(int id )
        {
                this.emp_id = id ;
        }
}

class Engineer extends Employee
{
        public Engineer(int id)
        {
                this.emp_id = id ;
        }
}

错误是这样的:

$ javac app.java 
app.java:25: cannot find symbol
symbol  : constructor Employee()
location: class Employee
        {
        ^
app.java:33: cannot find symbol
symbol  : constructor Employee()
location: class Employee
        {
        ^
2 errors

为什么会这样？

Answer 1

超类没有默认构造函数.所以你需要将适当的构造函数参数传递给超类:

super(id);

(将这个作为双方的顶线Manager和Engineer构造器.)您也应该删除this.emp_id = id线,在这两种情况下.

通常,如果构造函数不以super(...)or或this(...)语句开头(并且您只能使用其中一个,而不是两者),则默认使用super()(不带参数).