Java学习笔记5

 

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java 第五天
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(1)不要父类的某些方法.
继承复用: //不筛选的用继承关系把父类的所有代码完全的继承过来。
class Liucy {

       void techcpp() {

              System.out.println("TechC++");

       }

}

class Huxz extends Liucy {

}
组合复用:  // 设计原则: 组合优于继承,在代码复用的时候.
class Huxz1 {

       Liucy liucy = new Liucy();

       publicvoid techCpp() {

              liucy.techcpp(); // 方法的扩散.一个类调用另一个类的方法,而这个类又调用另一个类的方法.

       }

}
(2) 多态的应用.
多态用在返回值上; //理解不深刻,看看老师的代码:
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package test;

publicclass TestShape {

       publicstaticvoid main(String[] args) {

              Shape[] s = new Shape[3];

              s[0] = new Rect(5, 3);

              s[1] = new Square(4);

              s[2] = new Circle(10);

              for (int i = 0; i < s.length; i++) {

                     System.out.println(s[i].line());

                     System.out.println(s[i].area());

              }

       }

}

class Shape {

       publicdouble line() {

              return 0;

       }

       publicdouble area() {

              return 0;

       }

}

class Rect extends Shape {

       privatedoublechang;

       privatedoublekuan;

       public Rect() {

       }

       public Rect(double chang, double kuan) {

              this.chang = chang;

              this.kuan = kuan;

       }

       publicdouble line() {

              return (chang + kuan) * 2;

       }

       publicdouble area() {

              returnchang * kuan;

       }

}

class Square extends Rect {

       privatedoublebianChang;

       public Square() {

       }

       public Square(double bianChang) {

              this.bianChang = bianChang;

       }

       publicdouble line() {

              returnbianChang * 4;

       }

       publicdouble area() {

              returnthis.bianChang * this.bianChang;

       }

}

class Circle extends Shape {

       privatedoubler;

       public Circle(double r) {

              this.r = r;

       }

       publicdouble line() {

              return 2 * r * Math.PI;

       }

       publicdouble area() {

              returnr * r * Math.PI;

       }

}
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多态用在参数上;               
package test;

publicclass TestPoly {

       publicstaticvoid main(String[] args) {

              /*

               * int type=Integer.parseInt(args[0]); Animal a=getAnimal(type);

               * a.eat();

               */

              Dog d = new Dog();

              Cat c = new Cat();

              feed(d);// 传入不同的对象.

              feed(c);

       }

       publicstatic Animal1 getAnimal(int type) {

              if (type == 0)

                     returnnew Dog();

              else

                     returnnew Cat();

       }

       publicstaticvoid feed(Animal1 a) {

              a.eat();

       }

}

class Animal {

       publicvoid eat() {

       }

}

class Dog extends Animal1 {

       publicvoid eat() {

              System.out.println("Dog Eat Bone");

       }

}

class Cat extends Animal1 {

       publicvoid eat() {

              System.out.println("Cat Eat Fish");

       }

}
修改实现,对架构的影响最小.单继承:
接口像一个类的额外的信息().
java的多继承是有主次的,有主类型,附加的类型(副类型[接口]是一个附加信息.)
java中的多继承: 区分主类型和次要类型,接口的引用就使得我们可以对事物的共性,作一个再抽象.抽象出副类型.这种多继承的关系,是不会破坏单继承树状关系的复杂度.