类型转换

Animal a = new Cate();   //Animal是编译时类型，Cate是运行时类型。运行时类型得是编译时类型的子类
    引用类型      对象类型
    主观类型      客观类型

    以子类覆盖了父类的方法为前提 
    1）运行时类型不变 
    2）只能对一个引用调用其编译时类型中定义的方法
    3）运行时会根据对象的运行时类型找覆盖之后的方法
  
    Animal a = new Cate();
   Cate d = new Cate();
    a = d;      //把子类引用赋值给父类引用，是合法的
    d = (Cate)a; //把父类引用赋值给自类引用，需要强转
 
 
 父类的引用赋值给子类的引用需要强制类型转换 ，而子类的引用赋值给父类的引用不需要强制类型转换

public class Test {

	public static void main(String[] args) {

		Cat cat = new Cat();
		System.out.println("cat.CHARACTERISTIC = " + cat.CHARACTERISTIC);
		System.out.println("cat.getClass() = " + cat.getClass());
		System.out.println("cat.name = " + cat.name);
		System.out.println("cat.getName() = " + cat.getName());

		System.out.println("**********************************************");

		Animal animal = (Animal) cat;
		System.out.println("animal.CHARACTERISTIC = " + animal.CHARACTERISTIC);
		System.out.println("animal.getClass() = " + animal.getClass());
		System.out.println("animal.name = " + animal.name);
		System.out.println("animal.getName() = " + animal.getName());
	}
}

class Animal {
	public static String CHARACTERISTIC = "Can not speak.";
	public String name = "Animal";

	public String getName() {
		return name;
	}

}

class Cat extends Animal {
	public static String CHARACTERISTIC = "Can not speak. Like eat fish.";
	public String name = "Cat";

	public String getName() {
		return name;
	}
}

 

cat.CHARACTERISTIC = Can not speak. Like eat fish.
cat.getClass() = class Cat
cat.name = Cat
cat.getName() = Cat
**********************************************
animal.CHARACTERISTIC = Can not speak.
animal.getClass() = class Cat
animal.name = Animal
animal.getName() = Cat