java 继承中的构造方法

参考代码:
class SuperClass {
private int n;

SuperClass() {
System.out.println("SuperClass()");
}

SuperClass(int n) {
System.out.println("SuperClass(" + n + ")");
this.n = n;
}
}
class SubClass extends SuperClass {
private int n;

SubClass() {
//super();//父类构造方法必须放在子类构造方法第一行
System.out.println("SubClass()");
}

SubClass(int n) {
//super(n);//且如果子类构造方法中没有显示调用父类构造方法,者自动调用父类的无参构造方法.若父类无无参构造方法,则编译出错.
System.out.println("SubClass(" + n + ")");
this.n = n;
}
}
public class TestSuperSub {
public static void main(String arg[]) {
SubClass sc1 = new SubClass();
SubClass sc2 = new SubClass(400);
}
}