Java: Polymorphism in the downward transition +instanceof keyword __java

Animal.java:

Package com.imooc.animal;

public class Animal {
     private String name;
     private int month;
     
     
     Public Animal () {
    	 
     } public
     
     Animal (String name,int month) {
    	 this.setname (name);
         This.setmonth (month);
     }

     Eat () public
     void Eat () {System.out.println () the
    	 ability of animals to eat again. ");
     }
     
    Getter/setter public
	String GetName () {return
		name;
	}

	public void SetName (String name) {
		this.name = name;
	}

	public int getmonth () {return
		month;
	}

	public void setmonth (int month) {
		this.month = month;
	}
     
     
     
     
}

Cat.java:

Package com.imooc.animal;

public class Cat extends Animal {
      
	private String name;
	private int month;
	private double weight;
	
	Public Cat () {
		
	} public
	
	cat (String name,int month,double weight) {
		super (Name,month);//super Parent Class Property constructor method assignment
		setweight (weight);
	}
	
	Run public
	void Run () {
		System.out.println ("Cat will Run");
	}
	
	Method overrides
	@Override public
	void Eat () {
		System.out.println ("Cat eats fish.") ");
	}
	
	
	Getter/setter public
	String GetName () {return
		name;
	}

	public void SetName (String name) {
		this.name = name;
	}

	public int getmonth () {return
		month;
	}

	public void setmonth (int month) {
		this.month = month;
	}

	Public double Getweight () {return
		weight;
	}

	public void Setweight (double weight) {
		this.weight = weight;
	}
	
	
}

Test.java:

Package com.imooc.test;

Import Com.imooc.animal.Animal;
Import Com.imooc.animal.Cat;
Import Com.imooc.animal.Dog;

public class Test {public

	static void Main (string[] args) {
		Animal one=new Animal ();//1 Common Creation Instance
		one.eat (); 
  animal two=new Cat ();//2. Upward transition
		two.eat ();
		System.out.println ("=====================");
		
		*
		 * Downward transition (Forced transformation)
		 * Subclass references to instances (objects) of the parent class, where it must be customary to force type conversions
		 * This instance can invoke a subclass-specific method
		 * must satisfy the transition conditions to convert ()
		 * *
		cat temp= (CAT) two;//3. Downward transition, the original two is animal type, forcing type conversion to Cat
		temp.eat ();
		Temp.run ();
		Temp.setmonth (3);
		System.out.println ("Age:" +temp.getmonth ());
                /* Dog temp2= (Dog) two;
		Temp2.eat ();
		Temp2.sleep ();
		Temp2.getsex ();
		The above operation although the system does not complain, but the run throws an exception, the reason: two in the creation of the root is pointing to Cat (), so the above class to reduce to cat can be but turned into a dog will not do
		*}

}

Status of implementation

：

To solve the above problem:

Introduction of the instanceof keyword : instanceof is a Java, PHP two-dollar operator (operator), and ==,>,< is the same kind of things. Because it is made up of letters, it is also a reserved keyword in java. Its role is to determine whether its left object is an instance of its right class, and returns a Boolean type of data. Can be used to determine whether an instance of a subclass in an inheritance is an implementation of a parent class.

Instanceof generally placed in front of the type conversion, reasonable avoidance of abnormal production.

Package com.imooc.test;
Import Com.imooc.animal.Animal;
Import Com.imooc.animal.Cat;

Import Com.imooc.animal.Dog;
		
		public class Test {public static void main (string[] args) {Animal one=new Animal ();//1 Common Create Instance one.eat ();
		Animal two=new Cat ();//2. Upward transition two.eat ();
		
		System.out.println ("====================="); * * Downward transition (forced transformation) * Subclass references to instances (objects) of the parent class. Here must be used to force type conversions * This instance can invoke a subclass-specific method * must satisfy the transition conditions to convert (), the subclass can not be arbitrarily cast, but the subclass reference point to the parent class instance, you can strong Conversion * instanceof Operator: Returns TRUE/FALSE,/if (two instanceof cat) {cat temp= (cat) two;//3. Downward transition, originally two is animal type, coercion type conversion
		For Cat Temp.eat ();
		Temp.run ();
		Temp.setmonth (3);
		System.out.println ("Two can be converted to cat type");
		} if (two instanceof Dog) {Dog temp2= (Dog) two;
		Temp2.eat ();
		Temp2.sleep ();
		Temp2.getsex ();
		System.out.println ("Two can be converted to dog type");
		} if (two instanceof Animal) {System.out.println ("Two can be converted to Animal type");
		} if (two instanceof object) {System.out.println ("Two can be converted to type Object"); }
		
	}

}

Implementation status: