java class extends

Understanding inheritance is the key to understanding object-oriented programming. In Java, an existing class is inherited by the keyword extends, the inherited class is called the parent class (the superclass, the base class), an

upper bound wildcard character (Upper Bounds wildcards)" Nether wildcard (Lower Bounds wildcards)" 1. Why use wildcard characters and boundaries?In the process of using generics, a very awkward situation often arises. For example, we have the Fruit class, and its derived class, the Apple class, in the case of the main topic.class Fruit {}

method, unless the instance method contains a local variable with the same name as the member variable.Access to member variables requires the use of this.4. When a class contains more than one constructor method, if one of the constructor methods is to invoke another constructor method, use thepublic class this{Public this () {This ("white"); Using this method to construct a parameter in an argument-free

Keyword description ●? Wildcard type ● ● Extends example Static class food {}Static Class fruit extends food {}Static class Apple extends fruit {}Static class redapple

class is not inherited.But the constructor is another matter.2. Class initialization is performed only once, and when multiple objects are new to the same class, class properties and class initialization blocks are initialized only once.3. Modifiers in inheritance and prope

between them is:1. As we all know, Java is a single inheritance mechanism, and it is not allowed to inherit multiple classes at the same time. Therefore, when you inherit the thread class (extends thread), you can no longer inherit other classes. And you implement the Runnable interface is not the same, you can inherit other classes.2. When you inherit the threa

Differences between super T and extends T in Java generics The declaration of List Extends The wildcard declaration of List // Number "extends" Number (in this context) List // Integer extends Number List // Double

This article talks about Java Generic Declaration ? The extends e> is the Upper Bound (upper bound) wildcard that restricts the upper bounds of the type of the element, such as listIndicates that the upper bound of the element type in the collection is a fruit type, that is, only a subclass of fruit or fruit, so it is reasonable for the following assignment Fruits = new arraylistIf the parent

As we all know, to implement Java multi-threading Two ways A: is directly inherit the thread class, B: is to implement the Runnable interface.First on the code:A: The thread class is inherited directly,public class ThreadDemo1 extends Thread {public void Run () {Thread.Curre