Java：Inherited类构造函数调用Super类 [英] Java: Inherited class constructor is calling Super class

问题描述

在创建一个java程序时遇到一个问题，

While creating a java program i encountered a problem,

子类构造函数通过调用超类的方法抛出一个错误

A subclass constructor is throwing an Error by calling the Superclass's method

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 ;
        }
}

错误类似这样：

$ 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

推荐答案

超类没有默认构造函数。所以你需要传递适当的构造函数参数到超类：

The superclass doesn't have a default constructor. So you need to pass the appropriate constructor arguments to the superclass:

super(id);

（将此作为经理和 Engineer 构造函数。）在这两种情况下，还应删除 this.emp_id = id 行。

(Put this as the top line in both the Manager and Engineer constructors.) You should also remove the this.emp_id = id line, in both cases.

一般来说，如果你的构造函数不以 super（...）或 this（...）语句（和你只能有一个，而不是两个），然后它默认使用 super（）（没有参数）。

In general, if your constructor doesn't start with a super(...) or this(...) statement (and you can only have one of these, not both), then it defaults to using super() (with no arguments).

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