Java notes 3 polymorphism, java Polymorphism

Java notes 3 polymorphism, java Polymorphism
Polymorphism: --- multiple forms of an object essence: the reference of the parent class points to the subclass object --- premise: must inherit or implement class Animal {} class Dog extends Animal {} main {Dog d = new Dog (); // This state Animal dog = new Dog (); // polymorphism} Note: objects created in the form of polymorphism can only access member Methods common to sub-parent classes. The running result is that the sub-class result is a member method unique to the sub-class and cannot be used. Virtual method call: the unique method of the parent class object to call the sub-class Student S = new Student ("Zhang San", 100); Person p = new Student ("Li Si", 200); System. out. println (S. say (); System. out. println (p. say (); multi-state array-in an array of reference types, objects are stored in the form of polymorphism. Eg: Person [] person = {new Person ("Zhang San", 32), new Student ("Li Si", 21,120, 90.0), new Student ("Wang Wu", 22,119, 91.5), new Teacher ("instructor Liu", 35, 10, "Java EE"), new Teacher ("instructor Zhang", 11 )}; polymorphism parameter-reference type parameter instanceof operator in the method parameter list-determines whether an object is of the specified type (form) forced type conversion-converts an object from one type of reference to another type of reference object Association: one object uses one-to-one, one-to-many, many to one class test4 {public static void main (String [] args) {Person p = new Person ("", 50); method (p ); student S = new Student ("Michael", 100); method (S); Person p1 = new Student ("Zhao Si", 100); method (p1 );} public static void method (Person p) {if (p instanceof Student) {System. out. println ("instructor"); Student s = (Student) p; System. out. println ("local method call:" + p. say ();} else {System. out. println ("person");} System. out. println (p. say () ;}} class Person {private String name; private int age; public Person () {}public Person (String name, int age) {this. name = name; this. age = age;} public String getName () {return name;} public String say () {return "name:" + name + "age:" + age ;}} class Student extends Person {private int id; private double score; public Student (String name, int id) {this (name, 20, id, 98.5 );} public Student (String name, int age, int id, double score) {super (name, age); this. id = id; this. score = score;} public double getId () {return id;} public String say () {return super. say () + "student id:" + id + "score:" + score ;}}