P313多态属性类型无重写看编译类型
instanceOf 比较操作符
package com.Polymoraphic.Exercise;
public class PolyExcercise {
public static void main(String[] args) {
base base =new Sub();
//属性没有重写之说！属性的值看编译类型
System.out.println(base.count);//输出10
//instanceOf 比较操作符，用于判断对象的运行类型是否为XX 类型或XX 类型的子类型
System.out.println(base instanceof base);//true,运行类型Sub，是base子类
base bb = new base();
System.out.println(bb instanceof base);//true
}
}
class base{
int count =10;
}
class Sub extends base{
int count=20;
}
练习1
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//b===s,判断是b和s指向的对象的地址是否相同 //b.display()方法去找运行类型 //总结属性看编译类型，方法看运行类型
Java的动态绑定机制（非常重要）DynamicBindingP315
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package com.Polymoraphic.Exercise;
public class DynamicBinding {
public static void main(String[] args) {
//a 的编译类型A, 运行类型B
A a = new B();//向上转型
System.out.println(a.sum());//?40 -> 30
System.out.println(a.sum1());//?30-> 20
//a的运行机制是B，调用方法的时候先找子类的方法，没有,继承机制再找父类的方法
//比如只有父类的sum()方法时候有getI()。因为调用a对象的sum()方法时候
// 该方法会和该对象的内存地址/运行类型绑定，极为调用的是子类的getI(),20+10=30
//属性没有动态绑定机制，哪里声明哪里调用
//比如只有父类的sum1()方法时候，return i + 10，i在父类=10，所以10+10=20
}
}
class A {//父类
public int i = 10;
//动态绑定机制:
public int sum() {//父类sum()
return getI() + 10;//20 + 10
}
public int sum1() {//父类sum1()
return i + 10;//10 + 10
}
public int getI() {//父类getI
return i;
}
}
class B extends A {//子类
public int i = 20;
// public int sum() {
// return i + 20;
// }
public int getI() {//子类getI()
return i;
}
// public int sum1() {
// return i + 10;
// }
}
多态的应用--数组PolyArrayP315
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package com.Poly_polyer;
public class Person{
private int age;
private String name;
public Person(int age, String name) {
this.age = age;
this.name = name;
}
public String Say(){
return "t"+name+"t"+age;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
package com.Poly_polyer;
public class Student extends Person {
private double score;
public Student(int age, java.lang.String name, double score) {
super(age, name);
this.score = score;
}
//重写父类say方法;
public String Say(){
return "Student"+super.Say()+"t"+score;
}
public void student(){
System.out.println("学生 "+getName()+"正在学java");
}
public double getScore() {
return score;
}
public void setScore(double score) {
this.score = score;
}
}
package com.Poly_polyer;
public class Teacher extends Person{
private double salary;
public Teacher(int age, String name, double salary) {
super(age, name);
this.salary = salary;
}
public String Say(){
return "Teacher" +super.Say()+"t"+"salary"+salary;
}
public void teach(){//特有
System.out.println("teacher"+getName()+"正在讲课java ");
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
}
package com.Poly_polyer;
public class PloyArray {
public static void main(String[] args) {
//父类的引用指向子类的对象
Person[] persons=new Person[5];
persons[0] = new Person(20,"ka");
persons[1] = new Student(20,"skb",101);
persons[2] = new Student(22,"skc",102);
persons[3] = new Teacher(99,"wwa",9999);
persons[4] = new Teacher(90,"Bwa",6666);
//循环遍历多态数组
for (int i = 0; i < persons.length; i++) {
System.out.println(persons[i].Say());//动态绑定，看运行类型来调用
if(persons[i] instanceof Student){
Student students =(Student) persons[i];
students.student();
}else if(persons[i] instanceof Teacher){
((Teacher) persons[i]).teach();//一条语句更简洁
}else{
}
}
}
}
多态的应用--参数P318
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package com.poly_parameter;
public class Employee {
private String name;
private double msalary;
public Employee(String name, double msalary) {
this.name = name;
this.msalary = msalary;
}
public double getAnnual(){
return msalary*12;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getMsalary() {
return msalary;
}
public void setMsalary(double msalary) {
this.msalary = msalary;
}
}
package com.poly_parameter;
public class CustomEmployee extends Employee {
public CustomEmployee(String name, double msalary) {
super(name, msalary);
}
public void work(){
System.out.println("普通员工"+getName()+"在work...");
}
public double getAnnual(){
return super.getAnnual();//可以直接调用父类方法
}
}
package com.poly_parameter;
public class MEmployee extends Employee{
private double bonus;
public void manage(){
System.out.println("经理"+getName()+" 在manage");
}
public double getAnnual(){
return super.getAnnual()+getBonus();
}
public MEmployee(String name, double msalary, double bonus) {
super(name, msalary);
this.bonus = bonus;
}
public double getBonus() {
return bonus;
}
public void setBonus(double bonus) {
this.bonus = bonus;
}
}
package com.poly_parameter;
public class PolyParameter {
public static void main(String[] args) {
Employee ca = new CustomEmployee("yue",1);
Employee ma =new MEmployee("nyue",11,2);
PolyParameter p=new PolyParameter();
p.ShowEmployee(ca);//运行类型CustomEmployee
p.Testwork(ca);
System.out.println("=======");
p.ShowEmployee(ma);
p.Testwork(ma);
}
public void ShowEmployee(Employee e) {
System.out.println("annualsalary= " + e.getAnnual());
//动态绑定机制
}
public void Testwork(Employee e) {
if (e instanceof CustomEmployee) {
((CustomEmployee) e).work();//向下转型
} else if (e instanceof MEmployee) {
((MEmployee) e).manage();
}
}
}
P319 Object类详解
p319equals面试会用
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察看jdk方法的源码 ctr+b，或者点击方法，右键，goto-D or U
package com.Object;
public class Equals01 {
public static void main(String[] args) {
A a =new A();
A b=a;
A c=b;
System.out.println(a == c);//引用类型a指向A对象，bc也是，为true;
B bobj = a;//向上转型
System.out.println(bobj == c);//true地址同
int n1=10;
double n2=10.0;
System.out.println(n1==n2);//基本数据类型，true
System.out.println("hello".equals("abc"));;
//String的equals方法，源码怎么看ctr+b,源代码非常的经典
//第一判断是否是同一引用对象
// 第二个判断是否为字符串或者子类，判断长度，判断每个位置字符是否相等
//object的equals方法默认比较对象地址是否相同(两个对象是否相同)
//integer的equals方法，先判断是否是integer的子类或者integer类，然后判断值是否相等
Integer integer1 = new Integer(1000);
Integer integer2 = new Integer(1000);
System.out.println(integer1==integer2);//false,new了两次
System.out.println(integer1.equals(integer2));//true
String str1 = new String("hss");
String str2 = new String("hss");
System.out.println(str1 == str2);//false,new了两次
System.out.println(str1.equals(str2));//true
}
}
class A extends B{
}
class B{
}
重写equals方法P322
package com.Object;
public class EqualsExercise01 {
public static void main(String[] args) {
Person p1 = new Person("yy",20,'女');
Person p2 = new Person("xx",20,'女');
System.out.println(p1.equals(p2));//如果是没有重写，返回假，
// p1,p2是object的子类,判断位置，两个对象
//重写之后，返回为真
}
}
class Person{
private String name;
private int age;
private char gender;
public Person(String name, int age, char gender) {
this.name = name;
this.age = age;
this.gender = gender;
}
public boolean equals(Object obj){
//判断两个对象是否为一个对象，是返回true
if(this == obj){
return true;
}
//类型的判断
if(obj instanceof Person){//是Person,我们才能比较
Person p = (Person) obj;//进行向下的转行，获得obj的各个属性
return this.name.equals(p.name) && this.age==p.age && this.gender == p.gender;
}//如果不是person,直接返回true
return false;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public char getGender() {
return gender;
}
public void setGender(char gender) {
this.gender = gender;
}
}
String s1=new String("hsp");
String s2=new String("hsp");
system.out.println(s1==s2);//false,不是同一个对象
system.out.println(s1.equals(s2));//true,String重写了，先判断类型，再判断字符串
int a=9;//P324 double b=9f; System.out.println(a==b);//t,基本类型看值 char ch1 = 'A'; char ch2 = 12; System.out.println( 65== ch1);//T，AS码对应就是 System.out.println( 12 == ch2);//T，基本数据类型
P325hashcode
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