java继承中的构造方法

1.子类的构造过程必须首先调用其基类的构造方法。

 

2.子类可以在自己的构造方法中使用super（argument_list）指定调用基类的构造方法，但必须写在子类方法的第一行。

 

3.同理可用this（argument_list）调用本类的另外构造方法。

 

4.如果没有显示的调用基类的构造方法，则系统默认系统默认调用基类无参数的构造方法。

 

5.如果子类的构造方法中没有显示调用基类的构造方法，基类也没有无参数的构造方法，则编译出错。

 

6.如果在类的修饰前是public， 则默认构造函数访问权限是  public ，如果 没有显示采用public修饰，则 默认构造函数的访问权限是 friendly。

 

class Person {
    private String name;
    private String location;
    Person(String name) {
        this.name = name;
        location = "Beijing";
    }
    Person(String name, String location) {
        this.name = name;
        this.location = location;
    }
    public String info() {
        return "name: " + name + "  location: " + location;
    }
}

class Student extends Person {
    private String school;
    Student(String n, String l, String school) {
        super(n, l);
        this.school = school;
    }
    Student(String name, String school) {
        this(name, "beijing", school);
    }
    public String info() {
        return super.info() + "  school: " + school;
    }
}



public class Test {
    public static void main(String args[]) {
        Person p1 = new Person("A");
        Person p2 = new Person("B", "shanghai");
        System.out.println(p1.info());
        System.out.println(p2.info());

        Student s1 = new Student("C", "S1");
        Student s2 = new Student("C","Shenyang","S2");
        System.out.println(s1.info());
        System.out.println(s2.info());
    }
}

输出结果：

/*
name: A  location: Beijing
name: B  location: shanghai
name: C  location: beijing  school: S1
name: C  location: Shenyang  school: S2
*/