What are the basic knowledge contents of the downward transformation of Java?

In this article, the editor introduces in detail "what is the basic knowledge content of the downward transformation of Java", the content is detailed, the steps are clear, and the details are handled properly. I hope that this article "what is the basic knowledge content of the downward transformation of Java" can help you solve your doubts.

1. Concept

The downward transformation is that the parent object is transformed into a subclass object. We give a reference of a parent class reference of type Animal to a reference of type Bird, which is a downward transformation.

2. Format

Subclass object = (subclass) parent class instance

3. Pay attention

Forced type conversion must be carried out when making a downward transition.

4. Instance class Animal {public String name; public void eat () {System.out.println (this.name+ "eating");}} class Cat extends Animal {} class Bird extends Animal {public int age; public void fly () {System.out.println (this.name+ "takeoff");}} public class Test extends TestDemo {public static void main (String [] args) {Animal animal = new Animal () Bird bird = (Bird) animal;// must cast}}

The significance of the downward Transformation of Java

At the beginning of learning Java, I didn't pay attention to the downward transformation. It has not been clear about the meaning and purpose of the downward transformation, but it is not clear that it will not, and the process of development will certainly not be expected.

In fact, upward transformation and downward transformation are both very important. Maybe we usually see more upward transformation, and upward transformation is also easier to understand.

But will it be silly to transform downwards? I'm going to use a subclass instance object. First, I generate a subclass instance to assign a value to the parent class reference, and then forcefully transfer the parent class reference down to the subclass.

Quote, isn't this superfluous? I don't transition up or down, just use subclass instances.

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