1 package com.jq;
 2
 3 /**
 4  * 封装
 5  */
 6 public class PackageDemo {
 7     /**
 8      * 将抽象的事物共有的属性进行私有化
 9      */
10     private String name;
11     private int age;
12     /**
13      * 将不需要对外提供的属性进行私有化。
14      */
15     private String phone;
16
17     public String getName() {
18         return name;
19     }
20
21     public void setName(String name) {
22         this.name = name;
23     }
24
25     public int getAge() {
26         return age;
27     }
28     /*
29     可以对传入参数进行限定来适应业务需求
30      */
31     public void setAge(int age) {
32         if(age<0){
33             this.age = 1;
34         }else if(age>1000){
35             this.age=1000;
36         }else{
37             this.age = age;
38         }
39     }
40
41     /*
42      * 无需关注代码细节,只需调用即可
43      */
44     public void eat(){
45         System.out.println("吃东西");
46     }
47     /*
48         提高代码的重用性
49      */
50     public Object add(Double numa,Double numb){
51         return numa+numb;
52     }
53
54     public static void main(String[] args) {
55         //直接调用方法实现功能,降低了代码的复杂度,也无需关系代码的实现过程
56         System.out.println(new PackageDemo().add(1d,2d));
57     }
58 }

package com.jq;/*** 继承*/
abstract class  human {//抽取共有特征
    String name;int age;//抽取共有方法,特有行为让其子类实现public abstract void eat();@Overridepublic String toString() {return "human{" +"name='" + name + '\'' +", age=" + age +'}';}
}
class XiaoMing  extends human{public XiaoMing() {super.name="小明";super.age=25;}public void eat() {System.out.println("吃面");}
}
class XiaoLi  extends human{public XiaoLi() {super.name="小丽";super.age=18;}public void eat() {System.out.println("吃面");}
}
public class ExtendsDemo {public static void main(String[] args) {System.out.println(new XiaoMing());System.out.println(new XiaoLi());}}

package com.jq;/*** 多态*/
class Dog {String name="二哈";public void call(){System.out.println("汪汪汪汪");}}
class erha extends Dog {public void eat(){System.out.println("吃的一手好狗粮");}
}
class xiaomao {public void call(){System.out.println("喵喵喵");}}
public class PolymorphicDemo {public static void main(String[] args) {Object[] animal = {new erha(),new xiaomao()};for (Object o : animal) {/*Dog dog =(Dog)o;dog.call();以上代码会抛异常 java.lang.ClassCastException: com.jq.xiaomao cannot be cast to com.jq.Dog*/if(o instanceof Dog){Dog dog =(Dog)o;dog.call();}else if(o instanceof  xiaomao){xiaomao cat =(xiaomao)o;cat.call();}}}}