多态

 public class ParentChildTest {
      public static void main(String[] args) {
          Parent parent=new Parent();
          parent.printValue();
          Child child=new Child();
          child.printValue();
          
          parent=child;
          parent.printValue();
         
         parent.myValue++;
         parent.printValue();
         
         ((Child)parent).myValue++;
         parent.printValue();
         
     }
 }
 
 class Parent{
     public int myValue=100;
     public void printValue() {
         System.out.println("Parent.printValue(),myValue="+myValue);
     }
 }
 class Child extends Parent{
     public int myValue=200;
     public void printValue() {
        System.out.println("Child.printValue(),myValue="+myValue);
     }
 }

实验截图：

结果分析：

当子类与父类拥有一样的方法，并且让一个父类变量引用一个子类对象时，到底调用哪个方法，由对象自己的“真实”类型所决定。

二.动手动脑 动物园

1）源代码：

  import java.util.Vector;
  public class zoo4 {
      public static void main(String[] args) {
           Feeder f = new Feeder("小李");
           Vector<Animal> ans = new Vector<Animal>();         
           ans.add(new Lion());          
          for (int i = 0; i < 10; i++) {
              ans.add(new Monkey());
          }
          for (int i = 0; i < 5; i++) { 
              ans.add(new Pigeon());
          }                
          f.feedAnimals(ans);
    }
 } 
 class Feeder {
     public String name;
     Feeder(String name) {
         this.name = name;
    }
     public void feedAnimals(Vector<Animal> ans) {
        for (Animal an : ans) {
             an.eat();
             }
         }
 }
 interface Animal {
     public abstract void eat();
        } 
 class Lion implements Animal {
     public void eat() {
         System.out.println("狮子");
            }
}
class Monkey implements Animal {
    public void eat() {
         System.out.println("猴子");
             }
 }
 class Pigeon implements Animal {
     public void eat() {
       System.out.println("鸽子");
         }
 }

 

 

三.动手动脑

1）源代码：

   import java.util.*;
  public class Ex1115 {
      public static void main(String[] args) {
           Account a = new Account("11111111111","dsdf","20161115","256398",23.6);
           a.jiemian();
      }
   }
  
  class Account
 {
      private static final String JOptionPane = null;
     private  static String Id;
      private static String name;
     private static String date;
    private static String mima;
     private static double extra;
     
      Account(String i,String n,String d,String m,double e)//构造函数
     {
       Id=i;
          name=n;
         date=d;
          mima=m;
          extra=e;
      }
      
      public void set_Id(String i){
          Id=i;
      }
      public void set_name(String n){
          name=n;;
     }
      public void set_date(String d){
          date=d;
      }
      public void set_mima(String m){
          mima=m;
      }
      public void set_extra(double e){
          extra=e;
      }
      
      public String get_Id(){
          return Id;
      }
      public String get_name(){
          return name;
      }
      public String get_date(){
          return date;
      }
      public String get_mima(){
          return mima;
      }
      public double get_extra(){
          return extra;     }
     
      
      public static void jiemian()//界面
      {
          System.out.println("请选择界面(1.中文2.英文)：");
         Scanner sc=new Scanner(System.in);
          String num1=sc.nextLine();
          int num11=Integer.parseInt(num1);
         
          if(num11==1){
              
              Scanner sc1=new Scanner(System.in);
              int num=Integer.parseInt(sc1.nextLine());
  
              while(true)
              {
                      System.out.println("请选择要进行的操作：");
                      System.out.println("1.取款");
                      System.out.println("2.存款");
                      System.out.println("3.转账");
                      System.out.println("4.修改密码");
                     System.out.println("5.查询余额");
                     System.out.println("6.退卡");
                      
                if(num==1)
                   qukuan();
                else if(num==2)
                      cunkuan();
                else if(num==3)
                    zhuan();
                 else if(num==4)
                    xiugai();
                else if(num==5)
                      chaxun();
                 else if(num==6){
                     System.out.println("退卡成功！");
                 }
             }
         }
        
        else{
             
       }
     
    }
     
     public static void cunkuan()//存款
     {
         System.out.println("请输入存款金额：");
        Scanner sc = new Scanner(System.in);
         int jine = Integer.parseInt(sc.nextLine());
        
         extra += jine;
        System.out.println("您现在的金额为：" + extra);
    }
     
     public static void qukuan()//取款
     {
         System.out.println("请输入取款金额");
         String output="";
        output += "100  "
                 + "
500 "
                + "
1000  "
                 + "
1500 "
                 + "
2000 "
                 + "
5000  "
                 + "
其他金额（请输入0）"
                 + "
返回操作（请输入-1） "
                 + "
退卡（请输入-2）";
        System.out.println(output);
 
         Scanner sc=new Scanner(System.in);
         int num=Integer.parseInt(sc.nextLine());
        
         switch(num)
         {
         case 100:{
           
        }
             extra -= 100;break;
         case 500:
             extra -= 500;break;
         case 1000:
             extra -= 1000;break;
         case 1500:
            extra -= 1500;break;
        case 2000:
             extra -= 2000;break;
        case 5000:
             extra -= 5000;break;
         case 0:
         {
            System.out.println("请输入取款金额：");
             Scanner sc1=new Scanner(System.in);
             int jine=Integer.parseInt(sc1.nextLine());
            extra -= jine;
            sc1.close();
            break;
        }
        case -1:
             System.out.println("已返回操作界面");break;
         case -2:
             System.out.println("退卡成功！");break;
         }
    }
     
     public static void zhuan()//转账汇款
     {
         System.out.println("请输入转账行号:");
        Scanner sc = new Scanner(System.in);
         String hanghao = sc.nextLine();
         
         Scanner sc1 = new Scanner(System.in);
         int jine = Integer.parseInt(sc1.nextLine());
         
        extra -= jine;
         
        System.out.println("转账成功！");
     }
     
    public static void xiugai()//修改密码
    {
        System.out.println("请输入要修改的密码：");
         Scanner sc1 = new Scanner(System.in);
        String mi = sc1.nextLine();
         mima = mi;
     }
     
     public static void chaxun()//查询余额
    {
        System.out.println("余额为："+extra);
     }
    
}
结果截图：