java中的子类和父类简例

class Base {private String fatherName = "My name is base!";// 1.初始化fatherNamepublic Base() {display();// 2.由于子类Derived重写了display()方法，所以要跳到Base类中的display()方法}public void display() {System.out.println(fatherName);System.out.println();}}class Derived extends Base {private String subName = "I'm base's subClass!";// 4.给sunName赋值// 5.父类构造方法执行完了，开始执行子类的构造方法public Derived() {// super();display();}// 3.输出的时候还没有执行第四步，所以输出的subName为null(未赋值的subName)// 6.子类初始化完后再次执行子类的display(),输出已赋值的subNamepublic void display() {// super.display();// System.out.println();System.out.print("Derived中的display()：");System.out.println(subName);}}public class TestDerived {public static void main(String[] args) {// Base base = new Base();// System.out.println();Derived derived = new Derived();//derived.display();/** * 程序执行顺序为123456 * 输出结果为：  * Derived中的display()：null * Derived中的display()：I'm base's subClass! */}}