Java 类的封装、继承、多态

// 封装、继承、多态
class Person1{String name;int age;private int height;// 私有 封装public Person1(String name, int age){this.name = name;this.age = age;}public void talk(){System.out.println("This is father class talk() !");}public void setHeight(int h){if(h > 0)this.height = h;}public int getHeight(){return this.height;}
}// 继承（只能继承单个父类） extends father_class
class Student extends Person1{ // java 一个子类只能有一个父类String school;public Student(String name, int age, String school){super(name,age);//调用父类的构造方法,且必须放在第一行this.school = school;// super. 调用父类属性、方法super.name = "Ming";super.age = 19;// 私有属性不可修改// super.height = 178;super.setHeight(178);}@Overridepublic void talk() { // 重写父类方法System.out.println("This is sub class talk() !");super.talk();//还可以调用父类被覆写的方法}
}class test1{public static void main(String[] args){Student s1 = new Student("Michael",18,"BJTU");System.out.println("name: "+s1.name+", age: "+s1.age+", school: "+s1.school + ", height: " + s1.getHeight());s1.talk();Person1 p = new Student("Ming",19,"BJTU");p.talk();// 多态，父类对象通过子类实例化，调用的是子类的talkStudent s2 = (Student) p;//向下类型转换，需要强制，向上是自动转的s2.talk();// 如果 p 是由 Person1 new 出来的，此处报错}
}

输出：

name: Ming, age: 19, school: BJTU, height: 178
This is sub class talk() !
This is father class talk() !
This is sub class talk() !
This is father class talk() !
This is sub class talk() !
This is father class talk() !进程已结束,退出代码0