Java 多态

 1 class Mammal{}
 2 class Dog extends Mammal {}
 3 class Cat extends Mammal{}
 4 
 5 public class TestCast
 6 {
 7     @SuppressWarnings("unused")
 8     public static void main(String args[])
 9     {
10         Mammal m;
11         Dog d=new Dog();
12         Cat c=new Cat();
13         m=d;
14         //d=m;
15         d=(Dog)m;
16         //d=c;
17         //c=(Cat)m;
18 
19     }
20 }

 1 public class ParentChildTest {
 2     public static void main(String[] args) {
 3         Parent parent=new Parent();
 4         parent.printValue();
 5         Child child=new Child();
 6         child.printValue();
 7         
 8         parent=child;
 9         parent.printValue();
10         
11         parent.myValue++;
12         parent.printValue();
13         
14         ((Child)parent).myValue++;
15         parent.printValue();
16         
17     }
18 }
19 
20 class Parent{
21     public int myValue=100;
22     public void printValue() {
23         System.out.println("Parent.printValue(),myValue="+myValue);
24     }
25 }
26 class Child extends Parent{
27     public int myValue=200;
28     public void printValue() {
29         System.out.println("Child.printValue(),myValue="+myValue);
30     }
31 }

 1 public class TestInstanceof
 2 {
 3     @SuppressWarnings("unused")
 4     public static void main(String[] args) 
 5     {
 6         //声明hello时使用Object类，则hello的编译类型是Object，Object是所有类的父类
 7         //但hello变量的实际类型是String
 8         Object hello = "Hello";
 9         //String是Object类的子类，所以返回true。
10         System.out.println("字符串是否是Object类的实例：" + (hello instanceof Object));
11         //返回true。
12         System.out.println("字符串是否是String类的实例：" + (hello instanceof String));
13         //返回false。
14         System.out.println("字符串是否是Math类的实例：" + (hello instanceof Math));
15         //String实现了Comparable接口，所以返回true。
16         System.out.println("字符串是否是Comparable接口的实例：" + (hello instanceof Comparable));
17         String a = "Hello";
18         //String类既不是Math类，也不是Math类的父类，所以下面代码编译无法通过
19         //System.out.println("字符串是否是Math类的实例：" + (a instanceof Math));
20     }
21 }

 1 class Parent01
 2         
 3 {
 4     public int value=100;
 5     public void Introduce(){
 6             System.out.println("I‘m father");
 7     }
 8 }
 9 class Son extends Parent01
10 {
11     public int value=101;
12     public void Introduce(){
13         System.out.println("I‘m son");
14     }
15 }
16 class Daughter extends Parent01
17 {
18     public int value=102;
19     public void Introduce(){
20         System.out.println("I‘m daughter");
21     }
22 }
23 public class TestPolymorphism
24 {
25     public static void main(String args[]){
26         Parent01 p=new Parent01();
27         p.Introduce();
28         System.out.println(p.value);
29         p=new Son();
30         p.Introduce();
31         System.out.println(p.value);
32         p=new Daughter();
33         p.Introduce();
34         System.out.println(p.value);
35     }
36 }

  1 import java.util.*;
  2 public class ShowATM {
  3     @SuppressWarnings("resource")
  4     public static void main(String[] args) {
  5         Scanner in=new Scanner(System.in);
  6         ATM atm=new ATM();
  7         int choose=0,num=0;
  8         String pw="";
  9         next:while(true){
 10             System.out.println("是否进入账户（0否1是）：");
 11             int kk=in.nextInt();
 12             if(kk==0) break;
 13             else if(kk!=1){
 14                 System.out.println("输入错误！");
 15                 continue;
 16             }
 17             System.out.println("输入账户密码：");
 18             pw=in.next();
 19             if(atm.ifPass(pw)){
 20                 while(true){
 21                     showFace();
 22                     choose=in.nextInt();
 23                     switch(choose){
 24                     case 1:
 25                         System.out.println("输入存款金额：");
 26                         num=in.nextInt();
 27                         atm.save(num);
 28                         System.out.println("存款成功！");
 29                         System.out.println("当前余额："+atm.getRest()+"元");
 30                         break;
 31                     case 2:
 32                         System.out.println("请选择：");
 33                         int a[]={100,500,1000,1500,2000,5000};
 34                         for(int i=0;i<a.length;i++)
 35                             System.out.println((i+1)+"."+a[i]+"元");
 36                         System.out.println("7.其他");
 37                         int ch=in.nextInt();
 38                         if(ch>=1&&ch<=6){
 39                             if(atm.withdraw(a[ch-1]))
 40                                 System.out.println("取款成功！");
 41                             else
 42                                 System.out.println("余额不足！");
 43                         }
 44                         else if(ch==7){
 45                             System.out.println("请输入取款金额：");
 46                             num=in.nextInt();
 47                             if(atm.withdraw(num))
 48                                 System.out.println("取款成功！");
 49                             else 
 50                                 System.out.println("余额不足！");
 51                         }
 52                         else 
 53                             System.out.println("输入有误！");
 54                         System.out.println("当前余额："+atm.getRest()+"元");
 55                         break;
 56                     case 3:
 57                         System.out.println("账户号：");
 58                         String s=in.next();
 59                         System.out.println("转账金额：");
 60                         int i=in.nextInt();
 61                         if(atm.transfer(s, i))
 62                             System.out.println("转账成功！");
 63                         else
 64                             System.out.println("转账失败！");
 65                         System.out.println("当前余额："+atm.getRest()+"元");
 66                         break;
 67                     case 4:
 68                         System.out.println("输入六位数密码：");
 69                         String p=in.next();
 70                         atm.setPassword(p);
 71                         break;
 72                     case 5:
 73                         System.out.println("当前余额："+atm.getRest()+"元");
 74                         break;
 75                     default:
 76                         continue next;
 77                     }
 78                 }
 79             }
 80             else
 81                 System.out.println("密码错误！");
 82         }
 83     }
 84     //显示菜单方法
 85     public static void showFace(){
 86         System.out.println("********************");
 87         System.out.println("    1.存款：");
 88         System.out.println("    2.取款：");
 89         System.out.println("    3.转账汇款：");
 90         System.out.println("    4.修改密码：");
 91         System.out.println("    5.查询余额：");
 92         System.out.println("    6.退卡：");
 93         System.out.println("********************");
 94         System.out.println("请选择：");
 95     }
 96 }
 97 
 98 class PersonalAccount{
 99     private String passWord="123456";//密码
100     @SuppressWarnings("unused")
101     private String number;//银行卡号
102     private int money=0;
103     public int getMoney(){return money;}//余额
104     public void setPw(String s){passWord=s;}//设置密码
105     public void addMoney(int x){money+=x;}//加钱
106     public void minusMoney(int x){money-=x;}//减钱
107     public boolean whetherPwTrue(String s){//密码是否正确
108         if(s.equals(passWord))
109             return true;
110         else return false;
111     }
112 }
113 abstract class PATM{
114     public abstract boolean withdraw(int x);//取款
115     public abstract void save(int x);//存款
116     public abstract boolean transfer(String s,int x);//转账
117     public abstract boolean ifPass(String s);//判断输入的密码是否正确
118     public abstract int getRest();//查询余额
119     public abstract void setPassword(String s);//设置密码
120 }
121 class ATM extends PATM{
122     private String numbers[]={"6227000000000000071","6227000000000000072",
123             "6227000000000000073","6227000000000000074"};//数据库中已有的账户卡号
124     private PersonalAccount account=new PersonalAccount();
125     public boolean withdraw(int x) {
126         if(x>account.getMoney())
127             return false;
128         else{
129             account.minusMoney(x);
130             return true;
131         }
132     }
133     public void save(int x) {
134         account.addMoney(x);
135     }
136     public boolean transfer(String s, int x) {
137         //转账
138         //先判断转到账户号是否存在
139         //再判断余额是否足够
140         boolean flag=false;
141         for(int i=0;i<numbers.length;i++)
142             if(s.equals(numbers[i])) flag=true;
143         if(x>account.getMoney()) flag=false;
144         if(x<=account.getMoney()&&flag) account.minusMoney(x);;
145         return flag;
146     }
147     public boolean ifPass(String s) {
148         return account.whetherPwTrue(s);
149     }
150     public int getRest() {
151         return account.getMoney();
152     }
153     public void setPassword(String s) {
154         account.setPw(s);        
155     }
156 }