Java Abstract class

/****: Current Problems:    1.  The run method of the animal class is not described correctly.     2.  no mandatory subclass must override the Run method. Image class Application Scenario:     when we describe a class of things, we find that there is a certain kind of behavior,     but this behavior is currently not specific, then we can * * * Take a statement of this behavior, but      does not implement this behavior, which is what we call a "* * *" behavior, we need to use the * * * Image class.     *** the benefits of the Elephant class:  enforces that subclasses must implement the specified method. The details of the like class:    1.  if a function does not have a method body, the function must be decorated with an abstract modifier, which modifies the function as a function of the * *  .     2.  if a class appears with a function like * * *, then the class must also   use the abstract adornment.     3.  if a non-* * * * * * * * * * * * * * * * * * * Inherits the image class, all the image methods must be implemented. Otherwise, this class can only be a * * * Image class     4. *** like a non-* * * method, can also exist the method of the image.     5. ** * Like class can not exist * * * method. The      5. *** image class is not able to create objects.          question: Why can't the Elephant class create an object?          because * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *        Invoke * * * Image SquareThere is no point in the law. The     6. *** image class is a constructor, and its constructor is provided to the subclass to initialize the properties of the parent class when the object is created. *///Animal Class--->*** Elephant class abstract class animal{    string name;     string  color;    public animal (string  name,string  Color) {        this.name = name;     Methods of     this.color = color;    }//Non-* * * *      public void eat () {        system.out.println (name+) Eat food ");     }    //Mobile ...    public abstract  Void run ();  //as long as there is {}, is the implementation of the method}//dog   is a kind of animal  class Dog extends Animal{     public dog (String name,string color) {         super (Name,color);     }     public void run () {         System.out.println (name+ "Four legs run fast ...");     }}//fish   is a kind of class fish extends in animals.  animal{    public fish (String name,string color) {         super (Name,color);    }    public  Void run () {        system.out.println (name+) "Shake your tail and swim!" ");    }}class demo3 {    public static void  Main (String[] args)  {    /*    dog d = new  dog ("Shepherd Dog", "Brown");     d.run ();     //Create a Fish object      fish f  = new fish ("Koi", "golden");     f.run ();     */    animal&nbSp;a = new animal ();     }} 

/* Requirements:  describes a graph, circle,   rectangle of three classes. No matter which graph will have the calculation area and perimeter behavior, but each kind of graph calculation way is inconsistent. Naming conventions for constants: Capitalize all letters, separating words from words with underscores. Abstract cannot co-decorate a method with the following keywords, because someone else is rewriting a method that 1. abstract cannot co-decorate with private. 2. abstract  cannot work with static to modify a method. 3. abstract  cannot work with final to modify a method. *///abstract *** image//graphic class abstract class myshape{     string name;     public myshape (String name) {         this.name = name;    }    public  abstract  Void getarea ();     public abstract void getlength ();} Circular   is a kind of class circle extends myshape{    double r;  that belongs to graphic class    public static final double PI = 3.14;     Public circle (string name,double r) {    super (name);         this.r =r;    }    public  void  The area of Getarea () {        system.out.println (name+) is: "+PI*r*r);     }    public  void getlength () {         system.out.println (name+ "perimeter is:" +2*pi*r);     }}//rectangle   belongs to the   in the drawing A class rect extends myshape{    int width;    int  height;    public rect (string name,int width, int height) {         super (name);         this.width = width;        this.height = height;     }    public  void getarea () {        &nbSp The area of System.out.println (name+ "is:" +width*height);    }    public  The perimeter of  void getlength () {        system.out.println (name+) is: "+2* (Width+height));     }}class demo4{    public static void main ( String[] args)      {        // System.out.println ("hello world!");         circle c = new circle ("Round", 4.0);         c.getarea ();         C.getlength ();                         //Rectangle         Rect  R = new rect ("Rectangle", 3,4);         r.geTarea ();         r.getlength ();     }} 

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Java Abstract class